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Dr. Kennedy's Vocabulary Course: -H-
(View Course for 11/18/2013)
(A B C D E F G H I J K L M)
 
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Ron Kennedy, M.D.
 
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(A B C D E F G H I J K L M)
Haemophilus influenzae type B (HIB):   A bacterium capable of causing a range of diseases including ear infections, cellulitis (soft tissue infection), upper respiratory infections, pneumonia, and such serious invasive infections as meningitis with potential brain damage and epiglottitis with airway obstruction. It spreads by droplet through coughs and sneezing. Half of cases present as meningitis with fever, headache, and stiff neck. The remainder present as cellulitis, arthritis, or sepsis (bloodstream infection). About 5 percent of cases are fatal, Up to 20 percent of the survivors have permanent hearing loss. More than 90 percent of all HIB infections occur in children 5 years of age or younger-the peak attack rate is at 6 to 12 months of age. HIB causes 2 to 3 million cases of disease each year and about 450,000 deaths, the vast majority of them in developing countries today.
Helicobacter heilmannii:  A bacteria that infects most cats, dogs and pigs and, causes stomach inflammation (gastritis) in these animals. H. heilmannii is not usually transmitted from animals to people. But people who have been infected by H. heilmannii are known to have developed duodenal and gastric ulcers. Antibiotics can cure H. heilmannii infections. H. heilmannii and its better-known relative H. pylori are spiral bacteria that can colonize the stomach, cause chronic gastritis, and create duodenal ulcers and, to a lesser extent, gastric ulcers. H. pylori is now recognized as a risk factor for gastric adenocarcinoma and lymphoma.
Helicobacter pylori:  Bacteria that cause stomach inflammation (gastritis) and ulcers in the stomach. This bacteria is the most common cause of ulcers worldwide. It is often referred to as H. pylori. H. pylori infection is usually acquired from contaminated food and water and through person to person spread. The infection is common in crowded living conditions with poor sanitation. In countries with poor sanitation 90% of the adult population can be infected. In the U.S. 30% of the adult population is infected. One out of six patients with H. pylori infection develops ulcers of the duodenum or the stomach. This bacteria is also believed to be associated with stomach cancer and a rare type of lymph gland tumor called gastric MALT lymphoma. Infected persons usually carry the infection indefinitely, unless treated with medications to eradicate the bacteria.
Alternating Hemiplegia of Childhood (AHC):  A rare neurological disorder with frequent temporary episodes of paralysis of one side of the body (hemiplegia) usually beginning before the age of 18 months. The eye movements, face, or limbs can be paralysed on either side of the body, but on only one side at a time. The cause is unknown Also known as alternating hemiplegia syndrome.
H5N1 influenza (aka bird flu, avian influenza):  An influenza A virus subtype that occurs mainly in birds, is highly contagious among birds, and can be deadly to them. Outbreaks of avian influenza H5N1 occurred among poultry in eight countries in Asia during late 2003 and early 2004. At that time, more than 100 million birds in the affected countries either died from the disease or were killed in order to try to control the outbreaks. Since this outbreak, the virus has spread geographically. Reports of H5N1 infection in wild birds in Europe began in mid-2005. In early 2006, influenza A H5N1 infection in wild birds and poultry were reported in Africa and the Near East. Human cases of influenza A (H5N1) infection have been reported in several countries. Although H5N1 virus does not usually infect people, since November 2003 nearly 400 cases of human infection with highly pathogenic avian influenza A (H5N1) viruses have been reported by more than a dozen countries in Asia, Africa, the Pacific, Europe, and the Near East. Most of these cases have occurred from direct or close contact with infected poultry or contaminated surfaces; however, a few cases of human-to-human spread of H5N1 virus have occurred. Highly pathogenic avian influenza A (H5N1) viruses have never been detected among wild birds, domestic poultry, or people in the United States. Thus far, spread of H5N1 virus from person to person has been rare, but because all influenza viruses have the ability to change, scientists are concerned that H5N1 virus one day could be able to infect humans and spread easily from one person to another.
HAART (highly active antiretroviral therapy):  Treatment with a very potent drug "cocktail" to suppress the growth of HIV, the retrovirus thought to be at least partially responsible for AIDS.
Habitual abortion (aka recurrent abortion):  The miscarriage of 3 or more consecutive pregnancies. Habitual or recurrent abortion is a form of infertility. It is sometimes due to chromosome abnormalities or other genetic causes.
Habitus:  The physique or body build. Also the posture. For example, corticosteroid therapy can produce a characteristic cushingoid habitus with a moon face, "buffalo hump" at the back of the neck, and obesity of the trunk. (From the Latin for "condition" from the Latin verb habere meaning "to hold.")
Hair follicle:  A sac from which a hair grows and into which the sebaceous (oil) glands open. The follicle is lined by cells derived from the epidermal (outside) layer of the skin. Each follicle normally goes through a five-year cycle of growth and rest, with about 90% of the follicles growing hair at any one time, averaging about six inches (15 cm) of growth per year.
Hair loss:  Hair loss is the thinning of hair on the scalp. The medical term for hair loss is alopecia. Alopecia can be temporary or permanent. The most common form of hair loss occurs gradually and is referred to as androgenetic alopecia, meaning that a combination of hormones (androgens are male hormones) and heredity (genetics) is needed to develop the condition. Other types of hair loss include alopecia areata (patches of baldness that usually grow back), telogen effluvium (rapid shedding after childbirth, fever, or sudden weight loss); and traction alopecia (thinning from tight braids or ponytails). Hair loss normally occurs gradually with age in both men and women, but is typically more pronounced in men.
Hair of the dog:  An alcoholic chaser reputed to relieve a hangover, usually needed the morning after imbibing too much alcohol. There is no scientific evidence as to the efficacy of this time-honored treatment for a hangover. The saying originated in the belief that a cure for hydrophobia (rabies) or any disease contracted from a dog bite consisted of taking a hair of the dog that bit you and placing it in the wound.
Hair-on-end skull:  Thin fine linear extensions radiating out from the skull that look on an X-ray like hair standing "on-end" from the skull, an appearance associated with hemolytic anemias such as sickle cell disease and thalassemia. The "hair" represents the accentuated trabeculae extending between the inner and outer skull tables through the diploe in the expanded bone marrow space (because the bone marrow has expanded due to the excessive breakdown of red blood cells). The "hair" appears to be "on end" because the trabeculae are oriented perpendicular to the inner and outer tables of the skull.
Hairball (trichobezoar):  A wad of swallowed hair. Hairballs can sometimes be found to cause blockage of the digestive system, especially at the exit of the stomach. In some Far East cultures, hairballs are felt to have medicinal properties.
Hairy cell leukemia:  A form of chronic leukemia in which malignant B-lymphocytes (a type of white blood cell) are seen in the bone marrow, spleen, and peripheral blood and when viewed under the microscope, these cells appear to be covered with tiny hair-like projections. Hairy cell leukemia represents 2% of all leukemia. The disease includes marked enlargement of the spleen (splenomegaly), low red and white blood cell counts (pancytopenia), a relatively small number of circulating tumor cells with a hairy appearance, and infiltration of the spleen, liver, and bone marrow by the leukemic hairy cells. Splenectomy (surgical removal of the spleen) provides palliation (some help but not a cure). Treatment is usually with drugs, principally interferon alfa and purine analogues such as cladribine and pentostatin. For resistant cases, a promising immunotoxin has been developed that targets CD22, a molecule expressed exclusively on the surface of B-cells, including virtually all hairy cells.
Halitosis:  Bad breath. The most common cause is a "toxic colon." Other causes of halitosis include dietary factors, poor oral hygiene, tobacco use, certain chronic medical conditions, or dry mouth (as a side effect of medications, from mouth breathing, or from problems with the salivary glands leading to decreased production of saliva).
Hallervorden-Spatz disease:   A genetic disorder in which there is progressive neurologic degeneration with the accumulation of iron in the brain. It was first described by Julius Hallervorden and Hugo Spatz in 1922 in 5 sisters who showed increasing dysarthria (trouble speaking) and progressive dementia and, at autopsy, brown discoloration of specific parts of the brain (the globus pallidus and substantia nigra). The disease is characterized by progressive rigidity, first in the lower and later in the upper extremities. Involuntary movements of choreic or athetoid type may precede or accompany the rigidity. Both involuntary movements and rigidity may involve muscles supplied by cranial nerves, resulting in difficulties in articulation and swallowing. This disorder affects the muscular tone and voluntary movements progressively, making coordinated movements and chewing and swallowing almost impossible. Mental deterioration, emaciation, severe feeding difficulties, and visual impairment occur commonly in the late stages of the disease. The disease has its onset in the first or second decade of life. The average survival time after the diagnosis is made 11 years. Death usually occurs before the age of 30 years. The diagnosis of Hallervorden-Spatz disease has usually been made postmortem. However, magnetic resonance imaging (MRI) alterations in the basal ganglia of the brain now permit diagnosis during life in someone who has an affected sibling and is therefore at high (25%) risk for the disease.
Hallucination:  A profound distortion in a person's perception of reality, typically accompanied by a powerful sense of reality. An hallucination may be a sensory experience in which a person can see, hear, smell, taste, or feel something that is not there.
Hallucinogen:  A drug that causes hallucinations (profound distortions in a person's perceptions of reality). Under the influence of hallucinogens, people see images, hear sounds, and feel sensations that seem real but do not exist. Some hallucinogens also produce rapid, intense emotional swings. Hallucinogens cause their effects by disrupting the interaction of nerve cells and the neurotransmitter serotonin. Distributed throughout the brain and spinal cord, the serotonin system is involved in the control of behavioral, perceptual, and regulatory systems, including mood, hunger, body temperature, sexual behavior, muscle control, and sensory perception. LSD (an abbreviation of the German words for "lysergic acid diethylamide") is the drug most commonly identified with the term "hallucinogen" and the most widely used in this class of drugs. It is considered the typical hallucinogen, and the characteristics of its action and effects apply to the other hallucinogens, including mescaline, psilocybin, and ibogaine.
Hallux:  What the ancient Romans called the big toe. Since hallux was a good enough word for the big toe among the ancient Romans, it has long done yeoman's duty in medicine. Abnormalities of the big toe tend thus to be called hallux this-or-that.
Hallux valgus:  A big toe (the hallux) that is bent outward (valgus) so it overlaps the 2nd toe. A bunion is a localized painful swelling at the base of the big toe that can accompany hallux valgus. It is frequently associated with inflammation. It can be related to inflammation of the nearby bursa (bursitis) or degenerative joint disease (osteoarthritis).
Hallux varus:   An inward bending (varus) of the joint of the big toe (the hallux).
Hamartoma:  A benign (noncancerous) tumor-like growth consisting of a disorganized mixture of cells and tissues normally found in the area of the body where the growth occurs. One specific harmartoma is interesting and important to diagnose correctly, the hypothalamic hamartoma, which a benign tumor of the hypothalamus, the area of the brain that controls body temperature, hunger, and thirst. (In technical terms, the hypothalamus lies beneath a structure known as the thalamus and forms the floor of the third ventricle of the brain.) A small hypothalamic hamartoma can cause the patient to feel as though they have to laugh. The tumor also causes the patient to have mild epileptic seizures. The seizures can usually be controlled with medication; the laugh cannot. Larger hypothalamic hamartomas often cause more serious symptoms, including changes in mental ability and behavioral problems. Patients with possible hypothalamic hamartomas should have MRI scans, which should be thoroughly scrutinized, since the growths are small and sometimes difficult to detect.
Hammer toe:  A flexed (curled) but not abnormally rotated toe. May require surgical correction.
Hamstrings:  The two prominent tendons at the back of the knee and the muscles attached with flex the leg. The tendons are the sidewalls of the hollow behind the knee. (This hollow is called the popliteal space). A pulled hamstring is a common athletic injury. The "ham" of "hamstring" comes from an Old Teutonic word "ham" meaning crooked. This is in reference to the crooked part of the leg, that is the knee. To "hamstring" a person is to cripple him.
Hand, foot, and mouth disease:  A common illness of infants and children under 10 years old characterized by fever, sores in the mouth, and a rash with blisters due to infection most commonly with coxsackievirus A16 or less often enterovirus 71 or another enterovirus.
Hand-arm vibration syndrome (HAVS):  A disorder resulting from prolonged exposure to vibration, specifically to the hands and forearms while using vibrating tools. Symptoms include numbness, tingling, and loss of nerve sensitivity. The hand-arm vibration syndrome is a painful and potentially disabling condition of the fingers, hands, and arms due to vibration. There is initially a tingling sensation with numbness in the fingers. The fingers then become white and swollen when cold and then red and painful when warmed up again. Cold or wet weather may aggravate the condition. Picking up objects such as pins or nails becomes difficult as the feeling in the fingers diminishes and there is loss of strength and grip in the hands. The pain, tingling, and numbness in the arms, wrists and hands may interfere with sleep. Sources of vibration that can cause HAVS are very varied and include pneumatic drills, jackhammers, asphalt breakers, power chain saws, chipping tools, concrete vibrators and levelers, needle guns and scabblers, polishers, power jigsaws, sanders and angle grinders, riveters, compactors, power lawnmowers and even electronic games in which the hand controls vibrate. HAVS was first widely recognized as a potential occupational hazard in the mid-1980s. It was first known as "vibration white finger."
Handedness:  The preferential use of one hand for most fine manual tasks. Right handedness is the preferential use of the right hand while left handedness is the preferential use of the left hand for most fine manual tasks. Being able to use both hands equally well is known as being ambidextrous. Approximately 90% of the population is right-handed while about 10% is left-handed. A very small percentage of the population is ambidextrous. One study claimed that right-handed people live longer than lefties, as reflected by a decline in the proportion of lefties in the population with age. This study has since been repeatedly refuted.
Hangman's fracture:  A broken neck involving a fracture of an upper cervical vertebra similar to the injury suffered in death by hanging. The fracture always affects the vertebra called the axis -- the second cervical vertebra (C2) -- with or without subluxation (slippage) of C2 on C3. A hangman's fracture often causes death by suffocation.
Hangover:  A common nonmedical term for the disagreeable physical effects following excessive consumption of alcohol (or the use of other drugs). Veisalgia is the little-used medical name for the condition. It is also called a Spanish headache. Many researchers disagree on what may be the exact cause of the syndrome. Some feel that certain by-products that come from the liver's breakdown of alcohol may be responsible, others have postulated that "toxins" such as methanol found in high quantities in some drinks are responsible. To combat this unwanted side effect, it has been suggested that we eat foods rich in cysteine, such as eggs. The cysteine is used by the liver when it processes or metabolizes alcohol; therefore building back up this chemical may help. Another reasonable approach is to be sure to drink lots of water, since alcohol tends to dehydrate the body and brain. Some of the electrolyte rich drinks (e.g. Gator Aid) can also be of value. Lastly, blood sugar levels can decrease after alcohol use, so some extra sugar is advised by some experts.
Hansen bacillus:  Mycobacterium leprae, the agent of leprosy (Hansen disease).
Hansen's disease:  Leprosy, a chronic granulomatous infection caused by a bacterium which affects various parts of the body, including in particular the skin and nerves. (Granulomatous refers to the formation of granulomas, inflammatory nodules that are usually small, granular, firm, and persistent.) The bacterium responsible for leprosy is called Mycobacterium leprae.
Hantavirus:  A group of viruses that cause hemorrhagic fever and pneumonia. The Hantaviruses include the Hantaan virus that causes Korean (and Manchurian) hemorrhagic fever. The Hantavirus Pulmonary Syndrome (HPS) struck the Four Corner area (where the States of Arizona, New Mexico, Colorado, and Utah meet) in 1993 with devastating, frequently fatal consequences. Hantaviruses are transmitted to humans by contact direct or indirect with the saliva and excreta of rodents such as deer mice, field mice, and ground voles (a small rodent). The HPS outbreak in 1993 followed two years in which there was more rain, more foliage, and more deer mice than usual.
HAPE (High Altitude Pulmonary Edema):  the accumulation in the lungs of extravascular fluid (fluid outside of blood vessels) at high altitude, a consequence of rapid altitude ascent, especially when that ascent is accompanied by significant exercise. HAPE leads to dyspnea (shortness of breath), cough, tachycardia (fast heart rate) and decreased arterial oxygen levels. HAPE varies in degree from very mild to potentially fatal. Some people may be genetically susceptible to HAPE. People who develop HAPE have smaller lungs, higher pulmonary artery pressures, and higher pulmonary artery wedge pressures during exercise at sea level than those who do not develop HAPE. The incidence of HAPE has been analyzed in a prospective study of people climbing a 4500-meter mountain. 15% of climbers had clearcut evidence of HAPE from examination of the chest (by stethoscope or X-ray) after their climb. There is probably a risk of HAPE for most climbers if the rate of ascent and degree of physical effort are great enough. (Lancet Jan. 24, 2002). The planning and pacing of ascents is of critical importance. HAPE tends to be less frequent on well-planned ascents to much greater heights, despite the greater degree of hypoxemia (low blood oxygen levels).
Haploid:  A set of chromosomes containing only one member of each chromosome pair. The sperm and egg are haploid and, in humans, have 23 chromosomes. When they combine to produce a baby, they form the diploid (a set of 46 chromosomes in each cell).
Haploinsufficiency:  A situation in which the total level of a gene product (a particular protein) produced by the cell is about half of the normal level and that is not sufficient to permit the cell to function normally. Another way to define haploinsufficiency is as a condition that arises when the normal phenotype requires the protein product of both alleles, and reduction of 50% of gene function results in an abnormal phenotype. Haploinsufficiency can be due to a number of problems. One of the two copies of the gene may be missing due to a deletion. A mutation (change) in the gene may have wiped out the genetic source of the messager RNA responsible for 1/2 the production of the protein. Or the message or the protein produced by the cell may be unstable or degraded by the cell.
Hapten:  In immunology, a molecule that is incapable, alone, of causing the production of antibodies but which can do so when fastened to a larger antigenic molecule called a carrier.
Hapten:  A small molecule that can elicit an immune response only when attached to a large carrier such as a protein; the carrier may be one that also does not elicit an immune response by itself. (In general, only large molecules, infectious agents, or insoluble foreign matter can elicit an immune response in the body.) Once the body has generated antibodies to a hapten-carrier adduct, the small-molecule hapten may also be able to bind to the antibody, but it will usually not initiate an immune response; usually only the hapten-carrier adduct can do this. Sometimes the small-molecule hapten can even block immune response to the hapten-carrier adduct by preventing the adduct from binding to the antibody.
Hard measles:  An acute highly contagious viral disease with fever, runny nose, cough, red eyes, and a spreading skin rash. a potentially disastrous disease. Measles may be complicated by ear infections, pneumonia, encephalitis (that can cause convulsions, mental retardation. and even death), the sudden onset of low blood platelet levels with severe bleeding (acute thrombocytopenia purpura) or a chronic brain disease that occurs months to often years after an attack of measles (subacute sclerosing panencephalitis). During pregnancy measles may trigger miscarriages or premature delivery. Measles can be prevented through vaccination. The disease is also called (depending on how long you think it lasts) the seven-day measles, eight-day measles, nine-day measles, or the ten-day measles, and morbillis. The name measles comes from the Middle English maselen meaning many little spots referring, of course, to the rash.
Hard palate:  The bony part of the roof of the mouth. The hard palate is the front of the palate and is in front of (anterior to) the soft palate.
Hashimoto thyroiditis (autoimmune thyroiditis, Hashimoto disease):  A progressive disease of the thyroid gland characterized by the presence of antibodies directed against the thyroid, and by infiltration of the thyroid gland by lymphocytes. Hashimoto thyroiditis is the most common cause of hypothyroidism in North America and Europe. In this condition, the thyroid gland is usually enlarged (goiter) and has a decreased ability to make thyroid hormones. Hashimoto disease predominantly affects women, and can be inherited.
Hay fever:  A seasonal allergy to airborne particles characterized by itchy eyes, runny nose, nasal congestion, sneezing, itchy throat, and excess mucus. Hay fever is a misnomer because it is not caused by hay and it does not produce a fever. It is also known as allergic rhinitis or pollinosis.
HDL cholesterol:  Lipoproteins, which are combinations of lipids (fats) and proteins, are the form in which lipids are transported in the blood. The high-density lipoproteins transport cholesterol from the tissues of the body to the liver so it can be gotten rid of in the bile. HDL cholesterol is therefore considered the "good" cholesterol. The higher the HDL cholesterol level, the lower the risk of coronary artery disease. Even small increases in HDL cholesterol reduce the frequency of heart attacks. For each 1 mg/dl increase in HDL cholesterol there is a 2 to 4% reduction in the risk of coronary heart disease. Although there are no formal guidelines, proposed treatment goals for patients with low HDL cholesterol are to increase HDL cholesterol to above 35 mg/dl in men and 45 mg/dl in women with a family history of coronary heart disease; and to increase HDL cholesterol to approach 45 mg/dl in men and 55 mg/dl in women with known coronary heart disease. The first step in increasing HDL cholesterol levels is life style modification. Regular aerobic exercise, loss of excess weight (fat), and cessation of cigarette smoking cigarettes will increase HDL cholesterol levels. Moderate alcohol consumption (such as one drink a day) also raises HDL cholesterol. When life style modifications are insufficient, medications are used. Medications that are effective in increasing HDL cholesterol include nicotinic acid (niacin), gemfibrozil (Lopid), estrogen, and to a lesser extent, the statin drugs - which have so potentially serious side-effects many doctors consider them only in the case of familial hypercholesterolemia when total cholesterol is over 300.
HDR syndrome:  The syndrome of familial Hypoparathyroidism, sensorineural Deafness, and Renal dysplasia. It is inherited as an autosomal dominant trait and caused by haploinsufficiency of the GATA3 gene in chromosome 10p. The GATA3 gene appears essential to the embryonic development of the ears, parathyroid glands, and kidneys. The hypoparathyroidism causes hypocalcemia (a low level of calcium in blood), lifelong fatigue and depression. The deafness is congenital. The kidney dysplasia (malformations) can lead to nephrosis and progressive renal failure. Some patients have micrognathia (small chin) and no teeth. Supplemental calcium and vitamin D can increase the calcium, relieve the fatigue and depression and greatly improve quality of life.
Hearing loss, age-related (presbycusis):  the gradual progressive inability to hear, especially high frequency sounds. Presbycusis most often occurs in both ears. Because the loss of hearing is so gradual, people with presbycusis may not realize that their hearing is diminishing. They may have trouble distinguishing and understanding conversation in a noisy setting. Environmental exposures (such as to guns, power tools, industrial machinery, or very loud music) contribute significantly to presbycusis, but up to half of presbycusis is genetically determined. Presbycusis is common, affecting a third of people between 65 and 75 years and up to a half of people 75 and over. The hearing loss can usually be corrected with a hearing aid.
Hearing screening test, newborn:  Screening of the newborn baby's ability to hear. Newborn screening of hearing is done with automated auditory brainstem response tests or, less often, with what are called otoacoustic emission or conventional auditory brainstem response tests. The aim is to detect those babies with hearing deficits and teach them sign language in infancy or give them hearing aids or cochlear implants. The general purpose of all newborn screening tests is to detect treatable diseases. Most of these disorders are inheritedAs of 1999, only a handful of states in the U.S. mandated newborn hearing screening and only about 15% of all newborns were tested for their hearing in the hospital where they were born. The overall rate of hearing loss found in one study in the U.S. was about 1 in 330 newborns. The frequency of congenital hearing loss was 260 per 100,000 births (2-3 per thousand). This is a much higher incidence than for other conditions routinely screened for in newborns.
Heart:  The muscle that pumps blood received from veins into arteries throughout the body. It is positioned in the chest behind the sternum (breastbone; in front of the trachea, esophagus, and aorta; and above the diaphragm muscle that separates the chest and abdominal cavities. The normal heart is about the size of a closed fist, and weighs about 10.5 ounces. It is cone-shaped, with the point of the cone pointing down to the left. Two-thirds of the heart lies in the left side of the chest with the balance in the right chest. The heart is composed of specialized cardiac muscle, and it is four-chambered, with a right atrium and ventricle, and an anatomically separate left atrium and ventricle. The blood flows from the systemic veins into the right atrium, then to the right ventricle from which it is pumped to the lungs, then returned into the left atrium and to the left ventricle, from which it is driven into the systemic arteries. The heart is thus functionally composed of two hearts: the right heart and the left heart. The right heart consists of the right atrium, which receives deoxygenated blood from the body, and the right ventricle which pumps it to the lungs under low pressure; and the left heart, consisting of the left atrium, which receives oxygenated blood from the lung, and the left ventricle, which pumps it out to the body under high pressure. This is the pressure normally routinely measured as a screening procedure when you visit your doctor.
Heart and hand (Holt-Oram) syndrome:  A genetic syndrome characterized by the combination of heart disease and malformations of the upper limb. The heart defect is usually an atrial septal defect (ASD) and, less often, a ventricular septal defect (VSD), although other cardiovascular malformations have been reported. The upper limb malformations most often affect the forearm and thumb. The thumb may be absent or it may be a nonopposable fingerlike digit. All gradations in defects in the upper limb and shoulder girdle have been reported.
Heart attack:  The death of heart muscle due to the loss of blood supply. The loss of blood supply is usually caused by a complete blockage of a coronary artery, one of the arteries that supplies blood to the heart muscle. Death of the heart muscle, in turn, causes chest pain and electrical instability of the heart muscle tissue. The electrical instability of the heart can result in ventricular fibrillation (chaotic electrical disturbances affecting the ventricles, the lower chambers of the heart). Orderly transmission of electrical signals in the heart is important for the regular beating (and the efficient pumping) of the heart. A heart undergoing ventricular fibrillation simply quivers and can not pump or deliver oxygenated blood to the brain. Permanent brain damage and death can occur unless oxygenated blood flow is restored within five minutes. Many heart attack deaths are due to ventricular fibrillation that occurs before the victim can reach any medical assistance or the emergency room. These electrical disturbances of the heart can often be successfully treated with medications or other means by paramedics in the field, or upon arrival to the hospital. Approximately 90-95% of heart attack victims who reach the hospital survive. The 5-10% who later die are those who have suffered major heart muscle damage, or who suffer an extension orof their heart attack. Early heart attack deaths can be avoided if a bystander starts CPR (cardiopulmonary resuscitation) within five minutes of the onset of ventricular fibrillation. CPR involves breathing for the victim and applying external chest compression to make the heart pump. When paramedics arrive, medications and/or electrical shock (cardioversion) to the heart can be administered to convert ventricular fibrillation to a normal heart rhythm. Therefore, prompt CPR and rapid paramedic response can improve the survival chances from a heart attack. The treatment of a heart attack may include the prompt administration of drugs to dissolve and prevent blood clots; an angioplasty or intracoronary stenting to open an obstructed artery; and medications that open (dilate) blood vessels. Early reopening of a blocked coronary artery reduces the amount of heart muscle damage, lessens the size of the heart attack, and improves prognosis. Patients suffering a heart attack are usually hospitalized for several days to detect heart rhythm disturbance, and observe for shortness of breath and chest pain. A heart attack is also called a myocardial infarction (myocardium = "muscle heart") or MI.
Heart block:  A block in the conduction of the normal electrical impulses in the heart.
Heart conduction system:  The electrical conduction system that controls the heart rate. This system generates electrical impulses and conducts them throughout the muscle of the heart, stimulating the heart to contract and pump blood. Among the major elements in the cardiac conduction system are the sinus node, atrioventricular node, and the autonomic nervous system. The sinus node is the heart's natural pacemaker. The sinus (aka sinoatrial) node is a cluster of cells situated in the upper part of the wall of the right atrium. The electrical impulses are generated there. The electrical signal generated by the sinus node moves from cell to cell down through the heart until it reaches the atrioventricula (aka AV) node a cluster of cells situated in the center of the heart between the atria and ventricles. The AV node serves as a gate that slows the electrical current before the signal is permitted to pass down through to the ventricles. This delay ensures that the atria have a chance to fully contract before the ventricles are stimulated. After passing the AV node, the electrical current travels to the ventricles along special fibers embedded in the walls of the lower part of the heart. The autonomic nervous system (the same part of the nervous system as controls the blood pressure) controls the firing of the sinus node to trigger the start of the cardiac cycle. The autonomic nervous system can transmit a message quickly to the sinus node so it in turn can increase the heart rate to twice normal within only 3 to 5 seconds. This quick response is important during exercise when the heart has to increase its beating speed to keep up with the body's increased demand for oxygen.
Heart disease:  Any disorder that affects the heart. Sometimes the term "heart disease" is used narrowly and incorrectly as a synonym for coronary artery disease. Heart disease is synonymous with cardiac disease but not with cardiovascular disease which is any disease of the heart or blood vessels. Among the many types of heart disease, see, for example: Angina; Arrhythmia; Congenital heart disease; Coronary artery disease (CAD); Dilated cardiomyopathy; Heart attack (myocardial infarction); Heart failure; Hypertrophic cardiomyopathy; Mitral regurgitation; Mitral valve prolapse; and Pulmonary stenosis.
Heart failure:  Inability of the heart to keep up with the demands on it and, specifically, failure of the heart to pump blood with normal efficiency. When this occurs, the heart is unable to provide adequate blood flow to other organs such as the brain, liver and kidneys. Heart failure may be due to failure of the right or left or both ventricles. The signs and symptoms depend upon which side of the heart is failing. They can include shortness of breath (dyspnea), asthma due to the heart (cardiac asthma), pooling of blood (stasis) in the general body (systemic) circulation or in the liver's (portal) circulation, swelling (edema), blueness or duskiness of the entire body (cyanosis), and enlargement (hypertrophy) of the heart.
Heart hand (Holt-Oram) syndrome:  A genetic syndrome characterized by the combination of heart disease and malformations of the upper limb. The heart defect is usually an atrial septal defect (ASD) and, less often, a ventricular septal defect (VSD), although other cardiovascular malformations have been reported. The upper limb malformations most often affect the forearm and thumb. The thumb may be absent or it may be a non-opposable finger-like digit. All gradations in defects in the upper limb and shoulder girdle have been reported. The syndrome was first clearly delineated in 1960 by M. Holt and Samuel Oram as "Familial heart disease with skeletal malformations." Called also cardiac-limb syndrome, and atriodigital dysplasia.
Heart murmur:  An extra abnormal heart sound usually detected while listening to the heartbeat with a stethoscope. Heart murmurs may be harmless or may signal a problem, such as an abnormality of the heart valves or a congenital heart disease.
Heart muscle:  A type of muscle with unique features only found in the heart. The heart muscle, or cardiac muscle, is medically called the myocardium ("myo-" = muscle, cardium = heart).
Heart rate:  The number of heart beats per unit time, usually per minute. The heart rate is based on the number of contractions of the ventricles (the lower chambers of the heart). The heart rate may be too fast (tachycardia) or too slow (bradycardia). The pulse is the bulge of an artery from the wave of blood coursing through the blood vessel as a result of the contraction of the heart. It represents the high point of blood pressure. The pulse is often taken at the wrist to estimate the heart rate. A "normal" heart rate in a healthy adult at rest is around 60 per minute. In highly trained athletes the resting pulse can be as low as 28
Heart rhythm disorders:  Abnormal rhythm of the heart beat due to irregularities in transmission of the electrical signals that normally control heart rate and rhythm. Also known as arrhythmias. With an arrhythmia, the heart beats may be irregular or too slow (bradycardia), too rapid (tachycardia), or occur too early. When a single heartbeat occurs earlier than normal, it is called a premature contraction. An abnormal heart rhythm can be due to electrical disturbances in the upper chambers of the heart (atria), the atrioventricular (AV) node, or the lower chambers of the heart (ventricles). Examples of atrial arrhythmias include atrial fibrillation, atrial flutter, and paroxysmal atrial tachycardia. Ventricular arrhythmias include ventricular tachycardia and ventricular fibrillation.
Heart septum:  The septum of the heart is the dividing wall between the right and left sides of the heart. That portion of the septum that separates the two upper chambers (the right and left atria) of the heart is termed the atrial (or interatrial) septum while the portion of the septum that lies between the two lower chambers (the right and left ventricles) of the heart is called the ventricular (or interventricular) septum.
Heart test, EPS (ElectroPhysiologic Study of the heart):  A test of the electrical conduction system of the heart (the system that generates the heart beat). EPS is done by threading thin plastic tubes (catheters) into a vein where the leg connects to the abdomen. A local anesthetic is given as well as a mild sedative. The procedure is not painful and the patient is not put to sleep. After being placed into the vein, the catheters are then passed under fluoroscopic guidance into the heart. These catheters measure the electrical signals generated by the heart. They can a much more detailed analysis of these signals than a simple electrocardiogram (ECG). The catheters are used to rapidly pace the heart -- to make the heart beat quickly. The electrical conduction system of the heart is also measured during this rapid pacing and the heart is observed to see if any abnormal heart rhythms develop. The reason for doing EPS may to determine: (1) if a person needs a pacemaker. (This can usually be decided without an EPS but once in a while EPS is necessary.), (2) why a person is fainting (if other tests to find a basis have failed to find one), (3) If a person is prone to a fast heart rhythm (tachycardia) and guide the appropriate treatment for this abnormal heart rhythm, (4) whether past treatment for a fast heart rhythm has been satisfactory.
Heart transplant:  A surgical procedure in which a diseased heart is replaced with a healthy heart from a deceased person. The world's first heart transplant was done on December 3, 1967 by South African surgeon Christiaan Bernard (1922-2001). There have been two main barriers to successful heart transplants. The first barrier has been rejection of the donor heart by the patient, as occurred in the case of Dr. Blaiberg. Cyclosporine, which was introduced in 1983, and other medications to control rejection have greatly improved the survival of transplant patients. The second barrier to increasing the number of successful transplantations continues to be the availability of donor hearts.
Heart valves:  There are four heart valves. All are one-way valves. Blood entering the heart first passes through the tricuspid valve and then the pulmonary valve. After returning from the lungs, the blood passes through the mitral (bicuspid) valve and exits via the aortic valve.
Heart-lung machine:  A machine that does the work both of the heart (pump blood) and the lungs (oxygenate the blood). Used, for example, in open heart surgery. Blood returning to the heart is diverted through the machine before returning it to the arterial circulation. John H. Gibson invented the heart-lung machine which was first successfully used in open-heart surgery in 1953. Also called a pump-oxygenator.
Heartburn:  An uncomfortable feeling of burning and warmth occurring in waves rising up behind the breastbone (sternum) toward the neck. It is usually due to gastroesophageal reflux disease (GERD), the rise of stomach acid back up into the esophagus. Heartburn has nothing whatsoever to do with the heart. It is a popular nonmedical term. It is medically called pyrosis
Heartworm:  Dirofilaria immitis. A common parasite of dogs in many parts of the world that occurs in other animals, including cats, but rarely infects humans. The adult worms, which are up to 10 inches (25 cm) in length, typically live in the dog's pulmonary artery and right side of the heart. Inflammation and thickening of the heart may result in heart failure, respiratory insufficiency, chronic cough, and vomiting. The disease can be fatal. The female worms produce microfilariae that are found in the dog's blood. The microfilariae are ingested by a mosquito when it feeds on a dog, the microfilariae mature into infective juveniles in the vector, and the infection is transmitted to a new host when the mosquito feeds. Many species of mosquitoes serve as vectors for the heartworm. ProHeart 6, a twice-a-year time-released heartworm medication, was recalled in 2004 at the request of the FDA after thousands of dogs suffered adverse reactions, including liver and bleeding abnormalities followed in some cases by death. The active ingredient in ProHeart 6 is moxidectin. Other agents are available to treat heartworm.
Heat cramps:  Painful muscle spasms in the abdomen, arms, or legs following strenuous activity. The skin is usually moist and cool and the pulse is normal or slightly raised. Body temperature is mostly normal. Heat cramps often are caused by a lack of salt in the body, but salt replacement should not be considered without advice from a physician. Heat cramps usually affect people who sweat a lot during strenuous activity. The sweating depletes the body's salt and moisture. The low salt level in the muscles causes painful cramps. Heat cramps may also be a symptom of heat exhaustion. If you have heart problems or are on a low sodium diet, get medical attention for heat cramps. If medical attention is not possible, take these steps: (1) stop all activity, and sit quietly in a cool place, (2) drink clear juice or a sports beverage, (3) do not return to strenuous activity for a few hours after the cramps subside because further exertion may lead to heat exhaustion or heat stroke, (4) seek medical attention for heat cramps if they do not subside within 1 hour.
Heat exhaustion:  A warning that the body is getting too hot. The person may be thirsty, giddy, weak, uncoordinated, nauseous, and sweating profusely. The body temperature is usually normal and the pulse is normal or raised. The skin is cold and clammy. Although heat exhaustion often is caused by the body's loss of water and salt, salt supplements should only be taken with advice from a doctor. Heat exhaustion is the body's response to an excessive loss of water and salt contained in sweat. Those most prone to heat exhaustion are elderly people, people with high blood pressure and people working or exercising in a hot environment.
Heat index:  The temperature the body feels when heat and humidity are combined, the inverse of wind chill. The body dissipates heat by varying the rate and depth of blood circulation, by losing water through the skin and sweat glands, and as a last resort, by panting, when blood is heated above 98.6°F (37° C). Sweating cools the body through evaporation. However, high relative humidity retards evaporation, robbing the body of its ability to cool itself. When heat gain exceeds the level the body can remove, body temperature begins to rise, and heat related illnesses and disorders may develop.
Heat prostration (heatstroke, hyperthermia):  Overheating of the body due to extreme weather conditions. Unrelieved hyperthermia can lead to collapse and death, particularly in the elderly. Prevention via air conditioning, ventilation, and drinking extra water is the key for vulnerable persons. In emergency cases, injections of saline solution and rapid cooling of the body may be needed.
Heat rash:  Heat rash is an irritation of the skin that results from excessive sweating during hot and humid weather. Heat rash appears as clusters of red pimples or blisters on the skin. It is more likely to occur on the neck and upper chest, in the groin, under the breasts, and in elbow creases. Children are more likely than adults to develop heat rash. Heat rash is not a serious condition and can be easily treated by keeping the affected area cool and dry.
Heat stroke:  A core body temperature that rises above 104°F (40°C) accompanied by hot, dry skin and central nervous system abnormalities such as delirium, convulsions, or coma. Heat stroke occurs when the body becomes unable to control its temperature. The body's temperature rises rapidly, the sweating mechanism fails, and the body is unable to cool down. Body temperature may rise to 106°F (41.1°C) or higher within 10-15 minutes. Heat stroke can cause death or permanent disability if emergency treatment is not given. Heat stroke that results from exposure to a high environmental temperature is called non-exertional heat stroke. Heat stroke that results from strenuous exercise is called exertional heat stroke. Irrespective of type, heat stroke can be life thereatening. Immediate medical attention is essential when problems first begin. Symptoms may include confusion, combativeness, bizarre behavior, faintness, staggering, strong rapid pulse, dry flushed skin, lack of sweating, possible delirium or coma.
Heat syncope:  Sudden dizziness, feeling faint ans sometimes fainting experienced after exercising in the heat. The skin appears pale and sweaty but is generally moist and cool. The pulse may be weakened, and the heart rate is usually rapid. Body temperature is normal.
Heat-related illness:  A person with symptoms including headache, nausea, and fatigue after exposure to heat probably has some measure of a heat-related illness. It is important to recognize the difference between the very serious condition known as heat stroke and other heat-related illnesses. Persons experiencing any of these symptoms should consult a doctor.
Heatliness:  A characteristic of certain foods or other substances believed to cause emotional or physical reactions associated with temper, fever, passion, and excess. Coolness and heatliness are the yin and yang of a principle of Chinese philosophy. Heatiness produces a feeling of unpleasant warmth, stickiness of the eyes and dark urine. Certain foods and herbs are heaty while others are cooling. Chilies, fried fish and meat are heaty. Cucumbers, leafy vegetables and green tea are cooling. This system, of course, reminds us of high calorie vs. low calorie foods.
Heberden's disease:  Angina pectoris, chest pain that is often severe and crushing, due to an inadequate supply of oxygen to the heart muscle.
Heberden's node:  A small fixed bump on the finger, usually at the last joint of the finger, Heberden's node is a calcified spur of the joint cartilage and is a sign of osteoarthritis. Named for the English physician William Heberden (1710-1801) who made a number of celebrated medical discoveries (including angina).
Hecht (or Hecht-Beals) syndrome:  A striking genetic disorder in which abnormally short muscles in the jaw make it impossible to open the mouth fully (trismus) and abnormally short muscles in the hands keep the fingers straight when the hand is flexed back (pseudocamptodactyly). The difficulty in opening the mouth fully can cause severe infant feeding problems. It also complicates dental care and intubation for anesthesia. The hands may be so tightly fisted the infant crawls on his or her knuckles. The pseudocamptodactyly impairs manual dexterity and causes occupational and social disability. Many patients require surgical correction of contractures. The syndrome is considered a type of distal arthrogryposis.
Hecht's pneumonia:  Also known as giant cell pneumonia, this is a deadly but fortunately rare complication of measles. It tends to strike children who are immunodeficient as from leukemia or HIV/AIDS. The postmortem examination shows multinucleated giant cells lining the alveoli (air sacs) of the lungs. Named for the early 20th-century Austrian pathologist Victor Hecht.
Hedonophobia:  An abnormal, excessive, and persistent fear of pleasure. Sufferers with this most puritanical of phobias typically feel guilty about experiencing pleasure even though they usually realize rationally there is nothing at all wrong with taking pleasure. Their guilt usually arises from the fact that they are participating a pleasurable activity while others around them or in the world at large are experiencing nothing but illness, grief, economic hardship and other painful problems. Their guilt may also arise from the belief that life is best lived ascetically (similar to the idea that, for a medicine to do good, it must taste bad).
Heel bone:  Formally called the calcaneus. A more or less rectangular bone at the back of the foot. The words "calcaneus" and "calcium" come from the same source.
Heel prick (or stick):  A procedure in which the heel is pricked and then a small amount of the blood is collected, usually with a narrow-gauge ("capillary") glass tube or a filter paper. The heel prick is now the most common way to draw blood from newborns.
Heel spur:  A bony spur projecting from the back or underside of the heel that often makes walking painful.
Heimlich maneuver:  An emergency treatment for obstruction of the airway in adults. It may be needed when someone chokes on a piece of food that has "gone down the wrong way." To perform the Heimlich maneuver, stand behind the victim, wrap your arms around their waist, makes a fist with one hand and holds the fist with the thumb side just below the breast bone. Place your other hand over this first and use it to pull sharply into the top of the choking person's stomach and forcefully presses up into the victim's diaphragm to expel the obstruction (most commonly food). Repeat as necessary. In the early 1970s the American surgeon Henry Heimlich noted that food and other objects that caused choking by blocking the airway from the mouth to the lungs were not expelled by giving sharp blows to the back. In 1974 he devised a new method that he tested on laboratory dogs. The new manual thrust method -- the "Heimlich maneuver" -- is now in standard use. If the Heimlich maneuver is unsuccessful, an emergency tracheostomy may be needed to prevent suffocation.
HeLa cell:  One of the cells grown from the cervical cancer of a young African-American woman, Henrietta Lacks. HeLa cells were the first human cells to be continuously grown in culture. The cells were first cultured in February 1951 by Drs. George and Margaret Gey at Johns Hopkins in Baltimore. The cells appear "immortal" and are still used in medical research today. Who owns those cells? For many years, Lacks's children have sought recognition of their mother's contribution to science.
Helical CAT scan:  A new specialized CAT scan technique that involves continuous movement of the patient through the scanner with the ability to scan faster and with higher definition of internal structures. Helical CAT scanning can permit greater visualization of blood vessels and internal tissues, such as those within the chest cavity. This form of scanner may be particularly helpful in the rapid evaluation of severe trauma injuries, such as those sustained in automobile accidents.
Helicase:  An enzyme that unwinds double-strand DNA into two single DNA strands.
HELLP syndrome:  A syndrome featuring a combination of "H" for hemolysis (the breakdown of red blood cells), "EL" for elevated liver enzymes, and "LP" for low platelet count (an essential blood clotting element). The HELLP syndrome is a recognized complication of preeclampsia and eclampsia (toxemia) of pregnancy, occurring in 25% of these pregnancies.
Helminth:  A worm classified as a parasite. Helminth eggs contaminate food, water, air, feces, pets and wild animals, and objects such as toilet seats and door handles. The eggs enter the body of a human through the mouth, the nose and the anus. Once inside the body, helminth eggs usually lodge in the intestine, hatch, grow and multiply. They can sometimes infest other body sites.Examples of helminths are: roundworms, pinworms, tapeworms and flukes.
Helminthphobia:  An abnormal and persistent fear of being infested with parasitic worms called helminths.
Helper cell (aka CD4 cells, T-4 cells, T-helper cells, and helper T cells):  A type of T cell that participates in the immune response by recognizing foreign antigens and secreting substances called cytokines that activate T and B cells. Helper cells fall into two main classes: those that activate other T cells to achieve cellular inflammatory responses; and those that drive B cells to produce antibodies in the humoral immune response. These two classes of response are generally incompatible with one another and require coordination by substances called cytokines to promote one response while dampening the other. (The HIV virus attacks T-helper cells, knocking out the body's ability to defend itself against infections.) Helper cells have CD4 markers on their surface.
Hemangioma:  A birth irregularity where a localized tissue mass grows rich in small blood vessels. Capillary hemangiomas are composed nearly entirely of tiny capillary vessels. Cavernous hemangiomas are composed of blood- filled "lakes" and channels. A hemangioma may be visible through the skin as a birthmark, known colloquially as a "strawberry mark." Most hemangiomas that occur at birth disappear after a few months or years. Some progress to become serious deformations and if located in critical areas such as near the nasal cavity or within the bony orbit (containing the eye) serious and lasting functional damage may result. Little treatment other than plastic surgery is available in the U.S. However, in Germany special laser treatments are used to shrink hemangiomas which pose a risk to form or function. Hepatic hemangioma is the most common benign liver tumor and is 4-6 times more common in women than men (female hormones may promote its formation and growth). These tumors are usually small, a quarter inch (less than 1 cm) in diameter, cause no problems and are discovered incidentally in the course of testing for an unrelated medical problem. Large hepatic hemangiomas do occur, can cause symptoms -- pain, nausea, or enlargement of the liver -- and even rupture (a rare event) causing severe pain and bleeding into the abdomen that can be an emergency.
Hemarthrosis:  The presence of blood in a joint.
Hematemesis:  Vomiting blood.
Hematochezia:  Bright red blood in the stool, usually from the lower gastrointestinal tract -- the colon or rectum -- or from hemorrhoids. The term "hematochezia" is rarely used. "Bright red blood in the stool" is more widely used (and understood).
Hematocrit:  The proportion of the blood that consists of packed red blood cells. The hematocrit is expressed as a percentage by volume. The red cells are packed by centrifugation. For example, an hematocrit of 33% means that there are 33 milliliters of red blood cells in 100 milliliters of blood. In this case, the red cells would make up 1/3 of the blood. The normal ranges for the hematocrit are dependant on the age and, after adolescence, the sex of the individual. The normal ranges for the hematocrit are:
  • Newborns: 55-68%
  • One (1) week of age: 47-65%
  • One (1) month of age: 37-49%
  • Three (3) months of age: 30-36%
  • One (1) year of age: 29-41%
  • Ten (10) years of age: 36-40%
  • Adult males: 42-54%
  • Adult women: 38-46%
  • (These values may vary slightly between laboratories.)
The abbreviation for hematocrit is hct. In medical slang the hematocrit is called the crit.
Hematologist:  A physician who is specially trained in the diagnosis, treatment, and prevention of diseases of the blood and bone marrow as well as the immunologic, hemostatic (blood clotting) and vascular systems. Because of the nature of blood, the science of hematology profoundly affects the understanding of many diseases.
Hematology:  The diagnosis, treatment, and prevention of diseases of the blood and bone marrow as well as of the immunologic, hemostatic (blood clotting) and vascular systems. Because of the nature of blood, the science of hematology profoundly affects the understanding of many diseases.
Hematology-oncology:  The diagnosis, treatment and prevention of blood diseases (hematology) and cancer (oncology) and research into them. Abbreviated hem-onc.
Hematoma:  An abnormal localized collection of blood in which the blood is usually clotted or partially clotted and is usually situated within an organ or a soft tissue space, such as within a muscle. A hematoma is caused by a break in the wall of a blood vessel. The break may be spontaneous, as in the case of an aneurysm, or caused by trauma. The treatment of a hematoma depends on its location and size. Treatment can involve draining the accumulated blood. A hematoma in or near the brain is particularly dangerous.
Hematophobia:  An abnormal and persistent fear of blood is called hematophobia. Sufferers of this very common phobia dread the sight of their own blood, the sight of the blood of another person or an animal, and sometimes printed or filmed images of blood or even thoughts of blood. Blood may remind them of their own vulnerability to injury and of the eventuality of death.
Hematopoiesis:  The production of all types of blood cells generated by a remarkable self-regulated system that is responsive to the demands put upon it.
Hematuria:  Blood in the urine. Hematuria may or may not be accompanied by pain, but it is always abnormal and should be further investigated. Painful hematuria can be caused by a number of disorders, including infections and stones in the urinary tract. Painless hematuria can also be due to many causes, including cancer. refers to blood in the urine that can be seen with the naked eye. Microscopic hematuria refers to blood in the urine that is visible only under a microscope.
Hemidesmosomes:  Very small stud- or rivet-like structures on the inner basal surface of keratinocytes in the epidermis of skin. They are similar in form to desmosomes when visualized by electron microscopy. While desmosomes link two cells together, hemidesmosomes attach one cell to the extracellular matrix.
Hemidiaphragm:  Half of the diaphragm, the muscle that separates the chest cavity from the abdomen and that serves as the main muscle of respiration. Both hemidiaphragms are visible on X-ray studies from the front or back. The right hemidiaphragm is protected by the liver and is stronger than the left. The left hemidiaphragm is more often subject to rupture and hernia than the right. Weakness at the place where the esophagus passes through the diaphragm is called hiatal hernia and is associated with GERD (gastroesophageal reflux disease).
Hemihyperhidrosis:  Hyperhidrosis (excess sweating) confined to one side of the body. Hemihyperhidrosis may occur after a stroke.
Hemihypertrophy:  Asymmetric (unilateral) overgrowth (hypertrophy) of the skull, face, trunk, limbs, and/or digits, with or without visceral involvement. Hemihypertrophy may be an isolated finding in an otherwise normal individual, or it may appear as part of several syndromes, including the Wiedemann-Beckwith syndrome. Hemihypertrophy carries an increased risk of Wilms tumor (of the kidney), hepatoblastoma (liver cancer), and adrenal cancer. Other problems associated with hemihypertrophy include scoliosis and unequal leg length with walking difficulties.
Hemiparesis:  Weakness on one side of the body, usually associated with stroke.
Hemiplegia:  Paralysis of one side of the body, usually associated with stroke.
Hemithorax:  Half of the thorax or, more simply, one side of the chest. A chest with no separation of the hemithoraces is called a buffalo chest.
Hemizygous:  Having only a single copy of a gene instead of the customary two copies. For example, all of the genes on the single X chromosome in the male are in the hemizygous state. Also, the genes in egg and sperm are in the hemizygous state.
Hemochromatosis:   Hemochromatosis (iron overload) is an inherited disorder in how the body absorbs and stores iron. The excess iron gives the skin a bronze color and damages the liver and other organs. Diabetes is also a part of the syndrome due to damage to the pancreas.
Hemodialysis:  A medical procedure that uses a special machine (a dialysis machine) to filter waste products from the blood and to restore normal constituents to it. This shuffling of multiple substances is accomplished by virtue of the differences in the rates of their diffusion through a semipermeable membrane (a dialysis membrane). Although hemodialysis may be done for acute kidney failure, it is more often employed for chronic renal disease. Hemodialysis is frequently done to treat end-stage kidney disease. Under such circumstances, kidney dialysis is typically administered using a fixed schedule of three times per week.
Hemoglobin:  The oxygen-carrying pigment and predominant protein in the red blood cells. Hemoglobin forms an unstable, reversible bond with oxygen. In its oxygenated state it is called oxyhemoglobin and is bright red. In the reduced state it is called deoxyhemoglobin and is purple-blue.
Hemoglobin A:  Normal adult hemoglobin, the main type of hemoglobin after infancy. The A stands for Adult.
Hemoglobin A1C:  The main fraction of glycosylated hemoglobin (glycohemoglobin) which is hemoglobin to which glucose is bound. Hemoglobin A1C is tested to monitor the long-term control of diabetes mellitus. The level of hemoglobin A1C is increased in the red blood cells of persons with poorly controlled diabetes mellitus. Since the glucose stays attached to hemoglobin for the life of the red blood cell (normally about 120 days), the level of hemoglobin A1C reflects the average blood glucose level over the past 4 months. The normal level for hemoglobin A1C is less than 7%. Diabetics rarely achieve such levels, but tight control aims to come close to it. Levels above 9% show poor control, and levels above 12% show very poor control. It is commonly recommended that hemoglobin A1C be measured every 3 to 6 months in diabetes.
Hemoglobin E:  Normal embryonic hemoglobin, the main type of hemoglobin found in the human embryo. The E stands for embryonic and also for epsilon, the chain unique to embryonic hemoglobin.
Hemoglobin F:  Normal fetal hemoglobin, the predominant type of hemoglobin in the fetus and newborn. The F stands for Fetal.
Hemoglobin S:  The most common type of abnormal hemoglobin and the basis of sickle cell trait and sickle cell anemia. Hemoglobin S differs from normal adult hemoglobin (called hemoglobin A) only by a single amino acid substitution (a valine replacing a glutamine in the 6th position of the beta chain of globin). Recognition of this tiny change in the hemoglobin molecule marked the opening of molecular medicine.
Hemoglobinuria:  The presence of free hemoglobin in the urine, an abnormal finding, that may make the urine look dark.
Hemolysis:  The destruction of red blood cells which leads to the release of hemoglobin from within the red blood cells into the blood plasma.
Hemolytic anemia:  Anemia due to the destruction (rather than underproduction) of red blood cells.
Hemolytic disease of the newborn:  Abnormal breakup of red blood cells in the fetus or newborn. This is usually due to antibodies made by the mother directed against the baby's red cells. It is typically caused by Rh incompatibility, that is differences between the Rh blood group of the mother and baby. Severe hemolytic disease can cause anemia and heart failure. Less-severe cases include jaundice, and can lead to brain damage is left untreated. Also known as erythroblastosis fetalis.
Hemolytic uremic syndrome:  A condition characterized by the breakup of red blood cells (hemolysis) and kidney failure. There is clumping of platelets (the blood cells responsible for clotting) within the kidney's small blood vessels with resultant ischemia (reduced blood flow) leading to the kidney failure. The partial blockage of the blood vessels also leads to the destruction of red blood cells (hemolysis). Platelets are also decreased which can cause bleeding problems.
Hemophagocytic lymphohistiocytosis:  A rare, cancer-like disorder in which both histiocytes and lymphocytes proliferate and attack body tissues or organs. It can be an inherited condition, or it can occur as a result of immunosuppression (as in organ transplants) or infection. Most patients are young children. Treatment is by chemotherapy, and in some cases bone-marrow transplantation.
Hemophilia:  A group of inherited bleeding disorders in which the ability of blood to clot is impaired.
Hemophilia A:  Classic hemophilia, due to profound deficiency of factor VIII, a blood factor necessary to normal clotting. The hemophilia A gene is on the X chromosome, so females carry the gene. Each son of a female carrier stands a 50% chance of receiving the gene and having hemophilia. Treatment is by blood products that introduce clotting factor and replace lost blood. However, use of contaminated blood products exposed many people with hemophilia to HIV infection in the 1980s. Hemophilia A has affected the Russian royal house and other descendants of Queen Victoria of England.
Hemophilia B:  Hemophilia due to deficiency of coagulation factor IX in the blood which results in prolonged oozing after minor and major injuries, tooth extractions, or surgery. There is renewed bleeding after the initial bleeding has stopped. The gene for hemophilia B gene is on the X chromosome, so males are affected and females carry the gene. About 10% of carrier females are at risk for bleeding. Each son of a female carrier stands a 50 percent chance of receiving the gene and having hemophilia B. Treatment is by blood products that introduce clotting factor IX and replace lost blood. Hemophilia B is also called Christmas disease (so-named for the first patient studied in detail with the disease).
Hemophilia carrier (hemophilia heterozygote):  A female carrying a mutant gene for hemophilia on one of her two X chromosomes and a normal allele on her other X chromosome. Hemophilia carriers have concentrations of clotting factor VIII or IX of about 50% of normal and, hence, decreased coagulability. However, if they have a clinical bleeding tendency, it is usually very mild. Hemophilia carriers are less likely to die from heart disease than noncarrier women, probably due to their decreased blood clotting which, in turn, makes blockage of their coronary arteries less likely. This is similar to the effect obtained by taking aspirin.
Hemophobia:  An abnormal and persistent fear of blood. Sufferers of this very common phobia dread the sight of their own blood, the sight of the blood of another person or an animal, and sometimes printed or filmed images of blood or even thoughts of blood. Blood may remind them of their own vulnerability to injury and of the eventuality of death. Some sufferers of hemophobia experience a typical phobic reaction characterized by an increase in blood pressure and heart rate. Other sufferers experience an atypical phobic reaction characterized by a decrease in blood pressure and heart rate, causing paleness and weakness. They may even faint. Those with the latter reaction may develop a new fear: the fear of fainting.
Hemoptysis:  Spitting up blood or blood-tinged sputum.
Hemorrhage:  Bleeding or the abnormal flow of blood. The patient may have an internal hemorrhage that is invisible or an external hemorrhage that is visible on the outside of the body. Bleeding into the spleen or liver is internal hemorrhage. Bleeding from a cut on the face is an external hemorrhage.
Hemorrhagic:  Pertaining to bleeding or the abnormal flow of blood.
Hemorrhagic cyst:  This type of functional cyst occurs when bleeding occurs within a cyst. Symptoms such as abdominal pain on one side of the body may be present with this type of cyst.
Hemorrhagic diarrhea, E. coli:  Bloody colitis (inflammation of the bowel) caused by E. coli, usually by the strain E. coli 0157:H7. The diarrhea is severe with painful abdominal cramps, gross blood in the stool, and lasts for 6 to 8 days. Most commonly, E. coli 01257:H7 comes from eating raw or undercooked ground beef (hamburger) or from drinking raw milk or contaminated water. Less commonly, E coli O157:H7 can be transmitted from one person to another.
Hemorrhagic fever with renal syndrome:  A number of diseases, also known as hemorrhagic fever, characterized by an abrupt onset of high fever and chills, headache, cold and cough, and pain in the muscles, joints and abdomen with nausea and vomiting followed by bleeding into the kidney and elsewhere.
Hemorrhagic fever, epidemic:  A number of diseases characterized by an abrupt onset of high fever and chills, headache, cold and cough, and pain in the muscles, joints and abdomen with nausea and vomiting followed by bleeding into the kidney and elsewhere. Many arboviruses (including those in the families Togaviridae, Flaviviridae, Filoviridae, and Bunyaviridae) and the Hantaviruses, spread by rodents or biting insects, can cause epidemic hemorrhagic fever. The Ebola virus is a notorious cause of epidemic hemorrhagic fever.
Hemorrhoid:  A dilated (enlarged) vein in the walls of the anus and sometimes around the rectum, usually caused by untreated constipation but occasionally associated with chronic diarrhea. The symptoms start with bleeding after defecation. If untreated, hemorrhoids can worsen, protruding from the anus. In their worst stage, they must be returned to the anal cavity manually. Fissures can develop, and these may cause intense discomfort. Treatment is by changing the diet to prevent constipation and avoid further irritation, the use of topical medication, and sometimes surgery or sclerotherapy. Also known as piles.
Hemorrhoidectomy:  Surgical removal of hemorrhoids usually reserved for severe hemorrhoids if more conservative treatment measures fail to alleviate the symptoms (burning, itching, swelling, protrusion, bleeding, and pain). Hemorrhoidectomy may be done with a standard scalpel or with an ultrasonic scalpel to cut away hemorrhoids (a method that does not require sutures). Another sutureless method involves staples. Tissue from further in the anus is used to close the wound with surgical staples after the hemorrhoids are removed.
Hemostasis:  The stoppage of bleeding or hemorrhage. Also, the stoppage of blood flow through a blood vessel or organ of the body. Hemostasis is the arrest of bleeding, whether it be by normal vasoconstriction (the vessel walls closing temporarily), by an abnormal obstruction (such as a plaque) or by coagulation or surgical means (such as ligation). There is genetic regulation of proteins involved in physiological (naturally occurring) hemostasis and atherothrombotic disorders, including myocardial infarction and stroke. People with a family history of coronary heart disease, for example, are more likely to develop the disease themselves, indicating that genetic factors may be important in this form of unwanted hemostasis.
Hemostat:  A surgical instrument made for clamping a vessel and stopping bleeding or the flow of blood. Used in emergency situations as well as in surgery.
Hendra virus:  A virus, formerly called equine morbillivirus, that can cause illness in horses and humans. First identified in 1994 in Australia where the virus caused the death of two patients, one of pneumonia and the other of encephalitis that developed a year after the patient's initial exposure. Hendra virus is widely distributed in fruit bats in Australia, suggesting that fruit bats may be the natural host of the virus. Hendra virus-infected fruit bats have also been reported in Papua New Guinea.
Henna:  A coloring made from the leaves of the Egyptian privet, Lawsonia inermis. Approved only for use as a hair dye, not for direct application to the skin, as in the body-decorating process known as mehndi. This unapproved use of a color additive to henna makes these products adulterated and therefore illegal. Injuries to the skin can result from products marketed as henna.
HEPA filter:  Acronym that stands for High-Efficiency Particulate Arrestor. HEPA filters are used for isolation and immunocompromise units, operating rooms, removal of allergens from the air (for hay fever, asthma, etc.) and other applications where maximum reduction or removal of submicron particulate matter from air is required.
Hepar:  The liver or a preparation made from it. The term hepar is not often used today. It is a direct borrowing of the Greek hepar, liver.
Heparin:  An anticoagulant (anti-clotting) medication. Heparin is useful in preventing thromboembolic complications (clots that travel from their site of origin through the blood stream to clog up another vessel). Heparin is also used in the early treatment of blood clots in the lungs (pulmonary embolisms). A newer form of the drug heparin (brand names: Lovenox and Fragmin) that has a lower molecular weight than normal heparin, termed "low weight heparin" may be superior to regular (unfractionated) heparin in cases of unstable angina and other cardiac diseases.
Heparin-induced thrombocytopenia:  Low blood platelet count as a result of the medication heparin. Heparin is used to treat and prevent abnormal blood clotting. Heparin-induced thrombocytopenia can be mild or serious and even fatal.
Hepatic:  Having to do with the liver. Pronounced hi-'pa-tik. From the Latin hepaticus derived from the Greek hepar meaning the liver.
Hepatic artery:  An artery that distributes blood to the liver, pancreas and gallbladder as well as to the stomach and duodenal portion of the small intestine. It is a branch of the celiac arter which in turn comes off the aorta.
Hepatic duct:  A duct (tube that carries fluid) that carries bile from the liver into the common bile duct which conveys it to the duodenum (the upper part of the small intestine). There are three hepatic ducts: the right hepatic duct (which drains bile from the right half of the liver); the left hepatic duct (which drains bile from the left half of the liver); and the common hepatic duct (which is formed by the junction of the right and left hepatic ducts).
Hepatic ductular hypoplasia, syndromatic:  Also called Alagille syndrome or arteriohepatic dysplasia, this is a genetic disorder characterized by jaundice in the newborn period, liver disease with cholestasis, peripheral pulmonic stenosis and unusual face. Children with Alagille syndrome usually present with jaundice (yellowing of the skin and whites of the eyes) in the newborn period. Cholestasis (stagnant flow of bile from the liver) then develops with pruritis (itching), stools without the usual yellowing brown color, and enlargement of the liver and spleen. Peripheral pulmonic stenosis is a form of congenital heart disease (CHD). Other types of CHD also occur. The face has deep-set eyes, broad forehead, long nose with flat tip, prominence of the chin, and low-set or malformed ears. The outlook depends upon the degree of severity of the CHD and the liver disease (it can cause liver failure). The condition is an autosomal dominant trait meaning that the gene for it is on a non-sex chromosome (an autosome) and a single edition of the Alagille gene is sufficient to produce the disease. The gene has been discovered on chromosome 20 in band 20p12. The syndrome was first described by D. Alagille in the French medical literature in 1969.
Hepatic encephalopathy:  Brain dysfunction directly due to liver dysfunction, most often recognized in advanced liver disease. Hepatic encephalopathy may cause disturbances of consciousness and progress to coma. Hepatic coma is the end-stage of the process. In minimal hepatic encephalopathy (MHE), there may be subtle impairment of behavior, intelligence, and neuromuscular function. Driving ability may be diminished.
Hepatic hemangioma:  A common benign tumor of the liver made up of small blood vessels. It is 4-6 times more common in women than men. These tumors are usually small, a quarter inch (less than 1 cm) in diameter, cause no problems and are discovered incidentally in the course of testing for an unrelated medical problem. Large hepatic hemangiomas do occur and can cause symptoms -- pain, nausea, or enlargement of the liver -- and even rupture (a rare event) causing severe pain and bleeding into the abdomen that can be an emergency. When a hemangioma is suspected, the challenge for the physician is to be sure that it is in fact a hemangioma and not another type of tumor, particularly a malignant one. Most hepatic hemangiomas need no treatment. If a hepatic hemangioma is large and causing symptoms, it can be surgically removed.
Hepatitis:  Inflammation of the liver from any cause. Hepatitis is most often viral, due to infection with one of the hepatitis viruses (A, B, C, D, and E) or another virus (such as those that cause infectious mononucleosis, cytomegalovirus disease, or yellow fever). The main nonviral causes of hepatitis are alcohol and drugs. Hepatitis is a major public health problem. Approximately 400 million people have hepatitis B and 170 million have hepatitis C. Both cause chronic liver infection that can be fatal. Hepatitis B and C are implicated in 80% of cases of liver cancer, the fourth leading cause of cancer deaths in the world.
Hepatitis A:  Inflammation of the liver caused by the hepatitis A virus (HAV). HAV is usually transmitted from person to person by food or drink that has been contaminated with the stool of a person with hepatitis A. This type of transmission is called "fecal-oral." The virus is more easily spread in areas where there are poor sanitary conditions or where good personal hygiene is not observed. In 2003 there were hepatitis A outbreaks in the US associated with eating raw or lightly cooked green onions (scallions). Casual contact, as in a school, office, or other work settings, does not spread the virus. Hepatitis A can be transmitted by men (both adolescents and adults) who have sex with men. Hepatitis A outbreaks among men who have sex with men have been frequently reported. The virus can also be transmitted by illegal-drug use involving needles.
Hepatitis A immunization:  When immediate protection against hepatitis A (infectious hepatitis) is needed, immunoglobulins are used. Protection is effective only if given within 2 weeks of exposure and lasts but 2-4 months. Immunoglobulins can be used to protect household contacts of someone with acute viral hepatitis and travelers to regions with poor sanitation and high hepatitis A rates, when the traveler has to depart sooner than the vaccines can take effect (about 2 weeks). Travelers can receive the immunoglobulin and vaccine simultaneously and be protected immediately and for longer term. When immediate protection is not needed, hepatitis A vaccines are considered for individuals in high-risk settings, including frequent world travelers, sexually active individuals with multiple partners, homosexual men, individuals using illicit drugs, employees of daycare centers, and certain healthcare workers, and sewage workers.
Hepatitis B:  Inflammation of the liver due to the hepatitis B virus (HBV), once thought to be passed only through blood products. It is now known that hepatitis B can also be transmitted via needle sticks, body piercing and tattooing using unsterilized instruments, the dialysis process, sexual and even less intimate close contact, and childbirth. Symptoms include fatigue, jaundice, nausea, vomiting, dark urine, light stools. Diagnosis is by blood test. Treatment is via anti-viral drugs and/or hepatitis B immunoglobulin (HBIG). Chronic hepatitis B may be treated with interferon. Healthcare workers accidentally exposed to materials infected with hepatitis B and individuals with known sexual contact with hepatitis B patients are usually given both HBIG and the hepatitis B vaccine to provide both immediate and long-term protection. HBV infection can be prevented by the hepatitis B vaccine, and by avoiding activities that could lead to getting the virus.
Hepatitis C:  Inflammation of the liver due to the hepatitis C virus (HCV), which is usually spread by blood transfusion, hemodialysis, and needle sticks. HCV causes most transfusion-associated hepatitis, and the damage it does to the liver can lead to cirrhosis and cancer. Transmission of the virus by sexual contact is rare. At least half of HCV patients develop chronic hepatitis C infection. Diagnosis is by blood test. Treatment is via anti-viral drugs. Chronic hepatitis C may be treated with interferon, sometimes in combination with anti-virals. There is no vaccine for hepatitis C. Previously known as non-A, non-B hepatitis.
Hepatitis D:  Liver inflammation due to the hepatitis D virus (HDV), which only causes disease in patients who already have the hepatitis B virus. Transmission is via infected blood, needles, or sexual contact with an infected person. Symptoms are identical to those of hepatitis B. Chronic infection with HDV is currently treated with interferon, although it is not very successful. HDV infection can be prevented by the hepatitis B vaccine, and by avoiding activities that could lead to getting the virus.
Hepatitis E:  A form of liver disease characterized by inflammation of the liver due to infection with the hepatitis E virus (HEV). Usually a mild disease, hepatitis E but can in rare cases prove fatal, particularly in pregnant women.
Hepatitis G:  A virus first identified in 1995 that is genetically related to the hepatitis C virus but which does not cause hepatitis and, in fact, is not known to be responsible for any disease. Infection with the virus seems to be beneficial to HIV-infected patients. They enjoy longer survival if they are coinfected with this virus and HIV than if they have HIV alone.
Hepatobiliary:  Having to do with the liver plus the gallbladder, bile ducts, or bile.
Hepatoblastoma:  A malignant tumor of the liver. Hepatoblastoma occurs almost exclusively in young children, more commonly in boys than in girls. The diagnosis of hepatoblastoma is usually made after abdominal swelling (from liver enlargement caused by the tumor) is noticed. Although small tumors can sometimes be treated successfully with surgery, the prognosis with hepatoblastoma is generally poor
Hepatocellular carcinoma:  A tumor in which the cancer starts during adulthood in cells in the liver. Also called adult primary liver cancer, hepatoma and also hepatocarcinoma. Primary liver cancer (hepatocellular carcinoma) is the most common cancer in some parts of the world. It is still relatively uncommon in the US but its incidence is rising, principally in relation to the spread of hepatitis B and hepatitis C. People who have a disease of the liver called cirrhosis are also more likely to get adult primary liver cancer. Hepatitis B and C appear to be the most significant causes of hepatocellular carcinoma worldwide. People who have both hepatitis B and hepatitis C may be at a higher risk if they consume more than 3 oz. (80 grams) of alcohol a day. A first-degree relative with hepatocellular carcinoma also increases the risk.
Hepatology:  The field of liver disease. The liver is the body's largest organ and hepatology is a large field. It includes, but is not limited to, the study of acute and chronic hepatitis, viral hepatitis, cirrhosis, genetic and metabolic liver diseases and their complications, liver cancer, liver transplantation, drug metabolism (which depends largely upon the liver), and immunology as it pertains to the liver. Historically, hepatology grew out of gastroenterology and so became a subfield of it, although today it appears to be emerging as a freestanding medical specialty.
Hepatomegaly:  Enlargment of the liver.
Hepatosplenomegaly:  Enlargement of the liver and spleen.
Hepatotoxic:  Injurious to the liver. For example, acetaminophen (Tylenol) can be hepatotoxic as can many other chemicals, including, and especially, common drinking alcohol.
Herbal:  1. An adjective, referring to herbs, as in an herbal tea. 2. A noun, usually reflecting the botanical or medicinal aspects of herbs; also a book which catalogs and illustrates herbs. The word "herbal" was pronounced with a silent "h" on both sides of the Atlantic until the 19th century but this usage persists only on the American side.
Herbalism:  The practice of making or prescribing herbal remedies for medical conditions. Practitioners of herbalism may be licensed MDs, naturopaths, or osteopaths. They may also be unlicensed. Interested consumers should seek out knowledgeable, and preferably licensed, herbalists.
Herbalist:  One versed in herbal lore and, in regard to therapy, an herb doctor.
Herbicide:  A chemical designed to control or destroy plants, weeds, or grasses. Herbicides tend to have wide-ranging effects on non-target species (such as you).
Heredity:  Genetic transmission from parent to child.
Hermansky-Pudlak syndrome (HPS):  A genetic disorder characterized by albinism (with lack of pigment in the skin or eye), bruising and prolonged bleeding (due to defective blood platelets), and fibrosis of the lungs. There is occasionally also inflammatory bowel disease and impaired kidney function. All HPS patients suffer from varying degrees of albinism. The lack of pigment in the eye impairs their vision and often leads to involuntary rhythmic eye movements called nystagmus. The most serious health problems in HPS are the tendency to bruise easily and bleed and the progressive deterioration in lung function.
Hernia:  A general term referring to a protrusion of a tissue through the wall of the cavity in which it is normally contained. Common examples are inguinal hernia and hiatal hernia.
Herniated disc:  Rupturing of the tissue that separates the vertebral bones of the spinal column. The center of the disc, which is called the nucleus, is soft, springy and receives the shock of standing, walking, running, etc. The outer ring of the disc, which is called the annulus (Latin for ring), provides structure and strength to the disc. The annulus consists of a complex series of interwoven layers of fibrous tissue that hold the nucleus in place. A herniated disc is often referred to as a slipped disc. This term came from the action of the nuclear tissue when it is forced from the center of the disc. The nuclear tissue located in the center of the disc can be placed under so much pressure that it can cause the annulus to rupture. When the disc has herniated or ruptured, it may create pressure against one or more of the spinal nerves which can cause pain, weakness or numbness in the neck and arm. Other names for herniated discs are prolapsed and ruptured discs.
Herniation:  Abnormal protrusion of tissue through an opening. For example, a intervertebral disk (one situated between the vertebral bodies) can protrude and impinge on a nerve root.
Herniorrhaphy:  The surgical repair of a hernia. Herniorrhaphy may be done under local or general anesthesia using a conventional incision or a laparoscope.
Heroin:  Semisynthetic drug derived from morphine. Discovered in 1874, it was introduced commercially in 1898 by the Bayer company in Germany. The name heroin was coined from the German heroisch meaning heroic, strong. Heroin is stronger (more potent) than morphine.
Heroin addiction:  Physical addiction to heroin, often with concurrent use of other opiates when heroin itself is not available. Treatment is by withdrawal, either gradual or sudden. Medication may be used to ease the physical effects of withdrawal, which include cramping, nausea, and intense craving. Opiate blocker drugs, such as reboxetine (brand name: ReVia), may be used to speed up the withdrawal process and assist the addict with maintaining compliance. Counseling, 12-step groups such as Narcotics Anonymous, nutritional support, and often antidepressant medication to help re-regulate the nervous system are helpful adjunct treatments. Another method of treating addiction is prescribing methadone, a synthetic opioid liquid, as a substitute for heroin. In some European countries heroin itself is prescribed for addicts.
Herpangina:  A viral illness in which small, painful ulcers and sores are found inside the mouth. It is accompanied by sore throat and fever. Herpangina is most common in children aged 3-10 but can occur at any age. Herpangina is usually caused by Coxsackie group A viruses. The illness typically resolves within a week with no complications.
Herpes simplex type 1:  A herpes virus that causes cold sores and fever blisters in and around the mouth. In rare cases, as when someone's immune system is severely compromised, this virus can cause infection of the brain (encephalitis). Herpes simplex type 1 is also known as human herpesvirus 1 (HHV-1).
Herpes simplex type 2:  A herpes virus that causes genital herpes, which is characterized by sores in the genital area. Genital herpes is a sexually transmitted disease (STD). This virus, like herpes simplex type 1, can also cause infection of the brain (encephalitis) if the immune system is severely defective or compromised. The treatment of infection with herpes simplex type 2 is by topical or oral anti-viral medication. Herpes simplex type 2 is also known as human herpesvirus 2 (HHV-2).
Herpes zoster:  Also called shingles, zona, and zoster. The culprit is the varicella-zoster virus. Primary infection with this virus causes chickenpox (varicella). At this time the virus infects nerves (namely, the dorsal root ganglia) where it remains latent (lies low) for years. It can then be reactivated to cause shingles with blisters over the distribution of the affected nerve accompanied by often intense pain and itching.
Herpesvirus:  One of a family of double-stranded DNA viruses that cause common infections in humans. These include: herpes, CMV, chickenpox, shingles, mono, measles, and Kaposi sarcoma. The herpesviruses may live latently in a person for years or even decades without causing symptoms and then be activated and cause disease.
Herpetiform virus:  A virus with the characteristic shape and behavior of a virus in the herpes family. Not all members of the herpes virus family have been identified. Some herpetiform viruses may eventually be called herpes viruses, while others are merely similar.
Hershey-Chase experiment:  An extraordinarily important experiment in 1952 that helped to convince the world that DNA was the genetic material. Alfred Hershey (1908-1997) and his assistant Martha Chase (1923-2003) at the Cold Spring Harbor Laboratory showed that the DNA, not the protein, of the phage virus contains the phage genes.
Hetero-:  Combining form from the Greek "heteros" meaning "different." The opposite is "homo-" from the Greek "homos" meaning "same." For example, heterogeneous and homogeneous, heterosexual and homosexual, etc.
Heterochromia iridis:  A difference of color between the iris of one eye and the other. (A person with one brown and one blue eye has heterochromia iridis.) Also, a difference in color within an iris (sectoral heterochromia iridis).
Heteroclite:  Deviating from the ordinary; irregular or abnormal; anomalous. As, for example, retroviruses represent a heteroclite field of virology. From the Greek hetero- (different) + klinein (to lean, inflect).
Heteroerotic:  Having to do with sexual excitement toward the opposite sex. By contrast with alloerotic or homoerotic.
Heterokaryon::  A cell with two separate nuclei formed by the experimental fusion of two genetically different cells. (Heterokaryons, for example, composed of nuclei from Hurler syndrome and Hunter syndrome, both diseases of mucopolysaccharide metabolism, have normal mucopolysaccharide metabolism proving that the two syndromes affect different proteins and so can correct each other in the heterokaryon).
Heteromorphism:  Something different in form. Chromosome heteromorphisms are normal variations in the appearance of chromosomes.
Heterophyes:  A minute parasite that lives in the small intestine of humans, cats, dogs and other mammals who acquire it by eating raw or uncooked contaminated fish. Heterophyes is one of the smallest trematodes (parasitic flatworms) infecting humans. The main symptoms are diarrhea and abdominal pain. The lining of the small intestine may break down, permitting the parasite's eggs to enter the bloodstream and be carried to other organs, especially to the heart, liver, and brain, where they can cause serious disease, The diagnosis is based on the microscopic identification of eggs in the stool. Praziquantel (Biltricide) is the drug of choice.
Heteroplasia:  The replacement of normal tissue of the body by abnormal tissue or by malpositioned normal tissue, a tissue growing in the wrong place. for examplek, progressive osseous heteroplasia is a disorder in which bone develops in areas where bone is normally absent.
Heteroploid:  A different chromosome number than the normal number of chromosomes.
Heterosexual:  A person sexually attracted to persons of the opposite sex. Or a person who has sexual relations with the opposite sex. Colloquially known as "straight." Also, used as an adjective.
Heterotaxy:  The abnormal placement of organs due to failure to establish the normal left-right patterning during embryonic development. The morbidity (disease) and mortality (death) from heterotaxy are caused by congenital defects, especially congenital heart disease.
Heterotopic:   In the wrong place, in an abnormal place, misplaced.
Heterotrisomy:  Trisomy of different chromosomes. The occurrence of two children in the same family, one with trisomy 18 and the other with trisomy 21, is an instance of heterotrisomy.
Heterozygote:  A person possessing two different forms of a particular gene, one inherited from each parent. A heterozygote is also called a carrier. For example, a woman who is a heterozygote for cystic fibrosis (CF) carries the CF gene on one of her chromosomes number 7 and the normal paired (non-CF) gene at the same position on her other chromosome 7. She is a carrier for CF but has no signs or symptoms of the disease. A manifesting heterozygote is a person who manifests signs or symptoms of what is usually a recessive condition and ordinarily only is evident in someone who has two copies of the gene. A compound heterozygote has two different mutant forms of a particular gene.
Heterozygous:  Possessing two different forms of a particular gene, one inherited from each parent. A person who is heterozygous is called a heterozygote or a gene carrier. Heterozygous is in contrast to homozygous, the possession of two identical copies of the same gene.
HEV:  Hepatitis E virus.
Hex-A deficiency:  Tay-Sachs disease.
Hexadactyly:  The presence of an extra digit, a sixth finger or toe, which is a very common congenital malformation (birth defect).
Hexenmilch (witch's milk):  A folk term for the milk that often comes from the breast of a newborn baby. This temporary phenomenon is due to stimulation of the baby's breasts by the mother's hormones that cross the placenta during pregnancy. The ability of the baby's breasts to respond in this fashion is a mark of baby born at (or near) full-term. The breast of a baby born prematurely cannot enlarge or produce witch's milk (in German, Hexenmilch). The term "witch's milk" is sometimes applied broadly to milk from the nipple at any time other than during nursing. See also Galactorrhea.
Hexosaminidase A:  An enzyme which, when deficient, causes Tay-Sachs disease, a progressive fatal neurologic disorder concentrated in people of European Jewish (Ashkenazi) descent.
Hiatal:  Pertaining to an hiatus, an opening.
Hiatal hernia:  A part of the stomach protrudes through the diaphragm at the opening where the esophagus normally passes through the diaphragm.
Hiccough:  An extraordinary type of breathing movement involving a sudden intake of air due to an involuntary contraction of the diaphragm accompanied by closure of the vocal apparatus (glottis) of the larynx. A hiccough is also called a hiccup. The abrupt inspiration is the result of a sudden contraction of the diaphragm. Closure of the glottis then halts the incoming air. The column of air strikes the closed glottis to produce the characteristic sound: a hiccup. Hiccups are often rhythmic. If self-limited, they are just a minor nuisance, but prolonged hiccups can become a major medical problem. The word "hiccup" was in use by 1530. It is an instance of onomatopoeia, the imitation of natural sounds by words.
Hidradenitis suppurativa:  This is an illness characterized by multiple abscesses that form under the arm pits and in the groin area.
Hidrosis:  Sweating, the production of perspiration. Hidrosis is the Greek word for sweating.
Hidrotic:  Pertaining to hidrosis, sweating, the production of perspiration. (Hidrotic ectodermal dysplasia is the form of this hereditary disease in which the patient can sweat, as opposed to anhidrotic ectodermal dysplasia in which the patient is unable to sweat.)
High altitude:  defined on the following scale: (1) High altitude: 8,000 - 12,000 feet (2,438 - 3,658 meters); (2)Very high altitude: 12,000 - 18,000 feet (3,658 - 5,487 meters); and (3) Extremely high altitude: 18,000+ feet (5,500+ meters).
High altitude pulmonary edema (HAPE):  The accumulation in the lungs of extravascular fluid (fluid outside of blood vessels) at high altitude, a consequence of rapid altitude ascent, especially when that ascent is accompanied by significant exercise. HAPE leads to dyspnea (shortness of breath), cough, tachycardia (fast heart rate) and decreased arterial oxygen levels. HAPE varies in degree from very mild to potentially fatal. Some people may be genetically susceptible to HAPE. People who develop HAPE have smaller lungs, higher pulmonary artery pressures, and higher pulmonary artery wedge pressures during exercise at sea level than those who do not develop HAPE.
High altitude sickness:  physiological effect that may occur at high altitude. So what is high altitude? Most people can go up to 8,000 feet (2,438 meters) with minimal effects. If you have been at that altitude before and had no problems, you can probably return to that altitude without problems if (and only if) you are properly acclimatized. If you have not been to high altitude before, caution is strongly recommended. No specific factors such as age, sex, or physical condition are known to correlate with the susceptibility to altitude sickness. Some people are simply more susceptible than others. There is no telling, so caution is the better part of wisdom.
High blood pressure:  Also known as hypertension, high blood pressure is, by definition, a repeatedly elevated blood pressure exceeding 140 over 90 mmHg -- a systolic pressure above 140 with a diastolic pressure above 90. Chronic hypertension is a "silent" condition. It can cause blood vessel changes in the back of the eye (retina), abnormal thickening of the heart muscle, kidney failure, brain damage, and may lead to stroke and/or heart attack. Diagnosis is made only by measurement of blood pressure because the condition is usually witnout symptoms (thus it is called the "silent killer). No specific cause for hypertension is found in 95% of cases. High blood pressure is treated with regular aerobic exercise, weight reduction (if overweight), salt restriction, and medications. For people who are psychologically "allergic" to the idea or taking medications, this is a place to make an exception.
High blood sugar:  An elevated level of the sugar glucose in the blood. Also called hyperglycemia. High blood sugar is a finding in a number of conditions, most notably diabetes mellitus. Elevated blood glucose leads to spillage of glucose into the urine (glucosuria) so that the urine is sugary. (The term diabetes mellitus means "sweet urine.") Aside from diabetes, the many other causes of high blood sugar include just eating more sugar (or food) than usual, the presence of an infection or another illness, an injury and the stress of surgery. High blood sugar may produce few or no symptoms. When there are symptoms, they may be dry mouth, thirst, frequent urination, urination during the night, blurry vision, fatigue or drowsiness, weight loss, or increased appetite. An elevated level of blood sugar may be a useful independent indicator of heart disease risk. The risk of dying from heart disease has been found to rise as the level of blood glucose increases (regardless of age, weight, blood pressure, cholesterol and smoking status).
High protein diet:  A high protein diet is a type of weight loss plan that emphasizes consumption of high-protein-containing foods. There are many different kinds of high protein diets. Many high protein diets may be risky for overall health because they stress the consumption of meats and high protein foods containing saturated fat and a high percentage of overall fat. According to the American Heart Association guidelines, adults who are trying to lose weight and keep it off should eat no more than 30 percent of total daily calories from fat and less than 7 percent from saturated fat, which is difficult or impossible with many high protein diets. High protein diets may also restrict intake of important carbohydrates and low-fat dairy products.
High-grade lymphoma:  A lymphoma that grows and spreads quickly but has a better response to anticancer drugs than that seen with low-grade lymphomas. High-grade lymphomas include large cell, immunoblastic, lymphoblastic, and small noncleaved cell lymphomas. Also called an aggressive lymphoma.
Hip bursitis:  A bursa is a fluid-filled sac that functions as a gliding surface to reduce friction between moving tissues of the body. There are two major bursae of the hip. Bursitis is usually not infectious, but the bursa can become infected. Treatment of non-infectious bursitis includes rest, ice, and medications for inflammation and pain. Infectious bursitis is treated with antibiotics, aspiration, and surgery. Injection of certain steroids directly into an inflammed bursal sac usually terminates the bursitis.
Hip dislocation, congenital:  The abnormal formation of the hip joint in which the ball at the top of the thighbone (the femoral head) is not stable within the socket (the acetabulum). The ligaments of the hip joint may also be loose and stretched. The degree of instability or looseness varies. A baby born with this condition may have the ball of the hip loosely in the socket (subluxed) or the ball of the hip may be completely dislocated at birth. Untreated, the condition may cause legs of different lengths and a "duck-like" walk and lead to pain on walking and early osteoarthritis. There is a familial tendency. It usually affects the left hip and is more common in girls than boys, in first-born children and in babies born in the breech position. It is more common in Native Americans than in whites and is rarely seen in African-American children. One of the early signs that a baby has been born with a dislocated hip may be a clicking sound when the baby's legs are moved apart.
Hip fracture:  Broken bone in the hip, a key health problem among the elderly, usually due to a fall or other kind of trauma involving direct impact to the hip bone which has been weakened by osteoporosis. The part of the hip most often broken is the greater trochanter (the knobby end) of the femur (the thigh bone). In some cases it may be the break is spontaneous due to extreme osteoporosis, and is then followed by a fall.
Hip pointer:  Sportstalk for an iliac crest contusion (a bruise of the upper edge of the ilium, one of the hip bones).
Hip replacement, total::  Surgery in which the diseased ball and socket of the hip joint are completely removed and replaced with artificial materials. Invented in 1972 by British orthopedic surgeon John Charnley.
Hip, developmental dislocation of the (DDH):  The abnormal formation of the hip joint in which the ball at the top of the thighbone (the femoral head) is not stable within the socket (the acetabulum). The ligaments of the hip joint may also be loose and stretched. The degree of instability or looseness varies. A baby born with this condition may have the ball of the hip loosely in the socket (subluxed) or the ball of the hip may be completely dislocated at birth. Untreated, the condition may cause legs of different lengths and a "duck-like" walk and lead to pain on walking and early osteoarthritis.
HIPAA:  Acronym that stands for the Health Insurance Portability and Accountability Act, a US law designed to provide privacy standards to protect patients' medical records and other health information provided to health plans, doctors, hospitals and other health care providers. HIPAA took effect April 14, 2003.
Hippocampus:  An area buried deep in the forebrain that helps regulate emotion and memory. Functionally, the hippocampus is part of the olfactory cortex, that part of the cerebral cortex essential to the sense of smell. The hippocampus is so-called because its shape suggests that of a seahorse. From the Greek hippos (horse) = kampos (a sea monster).
Hippocrates:  (c.460-377BC) Great Greek physician on the Mediterranean island of Cos, who founded a medical school there, and is regarded as the "Father of Medicine." That is the standard view of Hippocrates. But, in truth, virtually nothing is known of the first physician named Hippocrates. There are considered to have been several by that name, all of them teachers at the famous medical school on the island of Cos. It was in the 5th century BC, however, that Hippocrates' name and image began to emerge as a leader in medical research and thought. Hippocrates is generally credited with turning away from divine notions of medicine and using observation of the body as a basis for medical knowledge. Prayers and sacrifices to the gods did not hold a central place in his theories, but changes in diet, beneficial drugs, and keeping the body "in balance" were the key.
Hippocratic Oath:  One of the oldest binding documents in history, the Oath written by Hippocrates is still held sacred by physicians: to treat the ill to the best of one's ability, to preserve a patient's privacy, to teach the secrets of medicine to the next generation, and so on.
Hippophobia:  An abnormal and persistent fear of horses. Sufferers of this fear experience undue anxiety even when a horse is known to be gentle and well trained. They usually avoid horses entirely rather than risk being kicked, bitten or thrown. They may also fear other hoofed animals such as ponies, donkeys and mules. This type of phobia may be triggered by a fall from a horse (which is probably why it is said that, after a fall from a horse, one should get right back on). "Hippophobia" is derived from the Greek "hippos" (horse) and "phobos."
Hirschsprung disease:  A congenital abnormality (birth defect) of the bowel in which there is absence of the ganglia (nerves) in the wall of the bowel. Nerves are missing starting at the anus and extending a variable distance up the bowel. This results in megacolon (massive enlargement of the bowel) above the point where the nerves are missing. (The nerves are needed to assist in the natural movement of the muscles in the lining of our bowels which move bowel contents through.) Hirschsprung disease is an important condition. It is the commonest cause of lower intestinal blockage (obstruction) in the newborn period and later in infancy and childhood, Hirschsprung disease is a cause of chronic constipation. The most common symptoms of the disorder are vomiting, constipation, distention (swelling) of the abdomen, and intestinal obstruction. There is a male predominance of about 4 to 1 in Hirschsprung disease -- 4 boys to each girl.
Hirsutism:  Having an overabundance of hair. A person with hirsutism is said to be hirsute (pronounced hir-suit).
Hirudin:  An anticoagulant ("bloodthinner"). Hirudin is the active principle in the salivary secretion of leeches. The name hirudin is from Hirudo medicinalis, the name of the medicinal leech. In 1884 John Haycraft in Strasbourg found that leeches contained a substance with anticoagulant properties. This anticoagulant in leech saliva was isolated in the 1950s and found to be an antithrombin (an inhibitor of thrombin). The primary chemical structure of hirudin was determined in 1976. The anticoagulant drugs desirudin and lepirudin (brand name: Refludan) are genetically engineered recombinant forms of hirudin.
Hirudotherapy:  The use of leeches for medical therapy. Sometimes referred to as the "treatment that sucks." From hirudin, the active principle in the salivary secretion of leeches that acts as a potent anticoagulant (bloodthinner).
His disease (His-Werner disease, trench fever):  (His-Werner disease, trench fever): This is a parasite (louse-borne) disease that was first recognized in the trenches of World War I and so was called trench fever. It is estimated to have affected more than a million people in Russia and on the war fronts in Europe. Trench fever was again a major problem in the military in World War II and is seen endemically in Mexico, Africa, E. Europe, and elsewhere. Urban trench fever occurs among the homeless people and people with alcoholism today. Outbreaks have been documented, for example, in Seattle, Baltimore (among injection-drug users), Marseilles (France) and Burundi. The cause of trench fever is Bartonella quintana (also called Rochalimaea quintana), an unusual rickettsial organism that multiplies in the gut of the body louse. Transmission of the rickettsia to people can occur by rubbing infected louse feces into abraded (scuffed) skin or into the conjunctivae (whites of the eyes). The disease is classically a 5-day fever. The onset of symptoms is sudden with high fever, severe headache, back pain and leg pain and a fleeting rash.
Histamine:  Substance in the body that plays a major role in many allergic reactions. Histamine dilates blood vessels and makes the vessel walls abnormally permeable. It is produced by basophils, mast cells, and others.
Histamine cephalalgia:  A distinctive syndrome of headaches, also known as cluster headache or migrainous neuralgia. The common pattern of cluster headache is termed "episodic" and is characterized by 1-3 short attacks of pain each day around the eyes, clustered over a stretch of 1-2 months, followed by a pain- free breathing period (average: a year). The other main pattern of cluster headache is termed "chronic" (and is also known as chronic migrainous neuralgia).
Histidine:  An amino acid, one of the 20 building blocks of protein. An essential amino acid, histidine is present in many proteins. Histidine is elevated in the blood and urine in a genetic condition called histidinemia. Decarboxylation of histidine results in the formation of histamine. Symbol: His.
Histiocyte:  A type of white blood cell, also called a macrophage, that is created by the bone marrow. They usually stay in place, but when histiocytes are stimulated by infection or inflammation they become active, attacking bacteria and other foreign matter in the body.
Histiocytic necrotizing lymphadenitis:  A disorder, also called Kikuchi disease, that typically causes "swollen glands" in the neck (cervical lymphadeniopathy) together with fever or flu-like symptoms. Laboratory test abnormalities include elevated erythrocyte sedimentation rate (ESR), and white blood count abnormalities (low neutrophil count and elevated lymphocyte count with atypical lymphocytes in the peripheral blood). Kikuchi disease is fairly common in young people, predominantly young women, in Asia.
Histiocytosis:  A rare but potentially deadly disorder with similarities to cancer, in which histiocytes start to multiply and attack the person's own tissues or organs. The result can be tissue damage, pain, development of tumor-like lumps called granulomas, fatigue, and other symptoms. If histiocytosis affects the pituitary gland, diabetes insipidus may also develop. Treatment is by radiation and chemotherapy, although for reasons unknown, some cases go into remission without treatment.
Histiocytosis X:  Now called Langerhan's cell histiocytosis. This disease is subclassified into eosinophilic granuloma, Letterer Siwe disease, and Hand-Schuller-Christian disease.
Histiocytosis, Hand-Schuller-Christian:  A disease in which histiocytes start to multiply and attack the tissues or organs of the patient. The disease usually affects children age 2 to 5, less often older children and adults. The most frequent sites of bony involvement are the flat bones of the skull, ribs, pelvis, and scapula. Chronic otitis media due to involvement of the mastoid and the temporal bone is common. Diabetes insipidus affects some patients, mainly children who have systemic disease. Up to 40% of children with it have short stature. Hand-Schuller-Christian disease is a form of Langerhan's cell histiocytosis.
Histiocytosis, Langerhans cell:  Histiocytosis in which the active histiocytes normally occur in the skin.
Histiocytosis, Letterer Siwe:  A severe disease in which histiocytes start to multiply and attack the tissues or organs of the patient starting in infancy with a scaly, sometimes itchy rash on the scalp, ears, abdomen, and creases of the neck and face. Raw skin may provide a portal of entry for germs, leading to sepsis. There are often draining ears, swollen glands, enlargement of the liver and spleen, liver disease, anemia and neutropenia (low white blood cells). Loss of appetite, irritability, failure to thrive, and respiratory symptoms may occur. Because of their appearance, these children may be misdiagnosed as abused. Letterer-Siwe disease is the most severe form of Langerhan's cell histiocytosis.
Histiocytosis, lipid:  A form of histiocytosis that affects lipid (fat) storage. Also known as Niemann-Pick disease, Erdheim-Chester disease. There have been approximately 200 cases recorded.
Histiocytosis, malignant:  Histiocytosis in which the histiocytes actually become cancerous. Treatment is by radiation and chemotherapy, and in some cases bone-marrow transplantation.
Histiocytosis, sinus:  A variant of histiocytosis in which the lymph nodes are the main site of histiocyte proliferation. The sinuses become filled with and distended by masses of histiocytes.
Histo:  Popular name for the fungus histoplasma (Histoplasma capsulatum). Also medical school slang for histology (the microscopic study of tissues).
Histocompatibility:  Literally, tissue compatibility. With full histocompatibility between a donor and recipient, tissue can be transplanted without being seen as foreign and being attacked by the immune system of the recipient.
Histology:  The study of the form of structures seen under the microscope. Also called microscopic anatomy, as opposed to gross anatomy which involves structures that can be observed with the naked eye. Traditionally, both gross anatomy and histology (microscopic anatomy) have been studied in the first year of medical school in the U.S.
Histone:  A protein around which DNA coils to form chromatin. Without this protein material, DNA could not organize into chromosomes, and life as we know it would not exist.
Histoplasma:  Full name: Histoplasma capsulatum. A microscopic fungus that causes the disease histoplasmosis. The fungus is found throughout the world in river valleys and soil where bird or bat droppings accumulate. The spores of the fungus are released into the air when contaminated soil is disturbed (for example, by plowing fields, sweeping chicken coops, or digging holes) and the airborne spores can then be inhaled into the lungs, the primary site of infection. In the US, the fungus is so common that in parts of Kentucky and Tennessee nearly 90% of adults show evidence of exposure by a positive histoplasma skin test. The fungus can be transferred by organ transplantation.
Histoplasmosis:  A disease caused by the fungus Histoplasma capsulatum. Most people with histoplasmosis have no symptoms. However, histoplasma can cause acute or chronic lung disease and progressive disseminated histoplasmosis affecting a number of organs. It can be fatal if untreated. Positive skin tests to Histoplasma occur in as many as 80% of the people living in areas where the fungus is common, such as the eastern and central United States. Infants, young children, and older persons, in particular those with chronic lung disease are at increased risk for severe disease. Disseminated disease is more frequently seen in people with cancer or AIDS.
HIV:  Acronym for the Human Immunodeficiency Virus, commonly believed to be the cause of AIDS (acquired immunodeficiency syndrome). HIV has also been called the human lymphotropic virus type III, the lymphadenopathy-associated virus and the lymphadenopathy virus. No matter what name is applied, it is a retrovirus. (A Mb>retrovirus has an RNA genome and a reverse transcriptase enzyme. Using the reverse transcriptase, the virus uses its RNA as a template for making complementary DNA which can integrate into the DNA of the host organism).
HIV infection, acute:  The body's initial reaction to infection by the HIV virus. Acute HIV infection is a flu-like syndrome that occurs immediately after a person contracts HIV (the human immunodeficiency virus 1, the agent that is a strong do-factor in the causation of AIDS). The syndrome is characterized by fever, sore throat, headache, skin rash and swollen glands (lymphadenopathy). This syndrome precedes seroconversion - the development of detectable antibodies to HIV in the blood as a result of the infection. It normally takes several weeks to several months for antibodies to the virus to develop after HIV transmission. When antibodies to HIV appear in the blood, a person will test positive in the standard ELISA (enzyme-linked immunosorbent assay). test for HIV.
HIV test:  A test for the human immunodeficiency virus, the cause of AIDS. HIV tests are designed to detect antibodies to the HIV virus or the HIV virus itself. The antibody tests are: (1) ELISA (enzyme-linked immunosorbent assay) - a screening test used to detect infection with HIV. If positive, the ELISA test is usually repeated, (2) Western blot - a test usually used to confirm the results of an ELISA. It can rule out a false-positive by distinguishing HIV antibodies from other antibodies that may react to the ELISA, (3) IFA (indirect fluorescent antibody) -- a test used like the less expensive Western blot to confirm the results of an ELISA. The premiere test that can identifies the genetic material, the RNA, of the HIV virus is called (3) PCR (the polymerase chain reaction). PCR can detect an early HIV infection before antibodies are evident and determine whether a baby born to an HIV-positive mother will have HIV. A test similar to PCR testing, called the branched DNA test, also detects the RNA of HIV.
Hives:  A raised, itchy area of skin that is usually a sign of an allergic reaction. It can be rounded or flat-topped but is always elevated above the surrounding skin. It reflects circumscribed dermal edema (local swelling of the skin). The hives are usually well circumscribed but may be coalescent and will blanch with pressure. They typically last less than 4 hours but they may stay for days or weeks. Approximately 20% of the population has experienced a bout of hives. The hives are also called urticaria. Pressure urticaria is a common type of hives that occurs after the skin has been under pressure, often the feet after standing or the buttocks after sitting for a long time or areas where clothing is tight. The hives are typically deep and invisible to the eye. The hives may begin hours after the pressure on the skin has ceased. The hives last 8 to 72 hours and may be painful, itchy, or burning.
HLA:  The major human histocompatibility system. HLA-typing is done before transplantation to determine the degree of histocompatibility. HLA is an acronym for Human Leukocyte Antigens.
HLA-B57:  An HLA type that is strongly associated with unusually slow progression of the human immunodeficiency virus (HIV) from the primary infection to AIDS. In other words, HLA-B57 provides some protection against HIV progression.
Hoarding (referring to pathological hoarding):  Excessive hoarding of material goods, a condition that affects up to 40% of people with obsessive compulsive disorder (OCD). Excessive hoarders, who fill their houses with accumulations of junk, usually newspapers, bags of old clothing and lists, tend to experience more anxiety, depression and social disability than OCD patients with other symptoms. Hoarders are also less likely to seek help. Pathological hoarders have decreased activity in the anterior cingulate, a brain structure involved in decision making and problem solving, compared with people with other OCD symptoms. The hoarders also show less activation than the healthy subjects in the posterior cingulate, an area involved in spatial orientation, memory and emotion. Hoarding may therefore have a distinctive basis in brain activity.
Hoarseness:  A term referring to abnormal voice changes. Hoarseness may be manifested as a voice that sounds breathy, strained, rough, raspy, or a voice that has higher or lower pitch. There are many causes of hoarseness, including viral laryngitis, vocal cord nodules, laryngeal papillomas, gastroesophageal reflux-related laryngitis, and environmental irritants (such as tobacco smoking). An accumulation of fluid in the vocal cords associated with hoarseness has been termed Reinke's edema. Reinke's edema may occur as a result of cigarette smoking or voice abuse (prolonged or extended talking or shouting). Rarely, hoarseness results from serious conditions such as cancers of the head and neck region.
Hodgkin disease:   A type of lymphoma, a cancer that develops in the lymph system, part of the body's immune system. Because there is lymph tissue in many parts of the body, Hodgkin disease can start in almost any part of the body. The cancer can spread to almost any organ or tissue in the body, including the liver, bone marrow, and spleen. The cancer cells in Hodgkin disease appear distinctive under a microscope (as Reed-Sternberg cells).
Hogwarts headache:  A generalized headache from spending many hours reading an unusually long volume such as one of J.K. Rowling's Harry Potter books. The pain resolves one to two days after the patient finishes the book. The term was coined by Dr. Howard J. Bennett in a Letter to the Editor of The New England Journal of Medicine on October 30, 2003. Dr. Bennett's letter was entitled "Hogwarts Headaches - Misery for Muggles." Hogwarts refers to Harry's alma mater -- Hogwarts School of Witchcraft and Wizardry.
Holandric inheritance:  Inheritance of genes on the Y chromosome. Since only males normally have a Y chromosome, Y-linked genes can only be transmitted from father to son.
Holoprosencephaly (HPE):  A relatively common birth defect of the brain, which often also affects facial features, causing closely spaced eyes, small head size, and sometimes clefts of the lip and roof of the mouth. Not all individuals with holoprosencephaly are affected to the same degree, even in families where more than one individual has this predisposition. The risk of reoccurrence is small in most families. The best diagnostic procedure is a brain scan (CT or MRI). There are a number of causes of HPE, including genetic alterations and environmental effects. The cause of HPE in any individual family may be unknown. Holoprosencephaly is characterized by the failure of the prosencephalon (the forebrain of the embryo) to develop. During normal development, the forebrain is formed and the face begins to develop in the fifth and sixth weeks of pregnancy. Holoprosencephaly is caused by a failure of the embryo's forebrain to divide to form bilateral cerebral hemispheres (the left and right halves of the brain), causing defects in the development of the face and in brain structure and function. There is no treatment for holoprosencephaly and the prognosis for individuals with the disorder is poor. Most of those who survive show no significant developmental gains. For children who survive, treatment is symptomatic.
Holt-Oram syndrome:  A genetic syndrome characterized by the combination of heart disease and malformations of the upper limb. The heart defect is usually an atrial septal defect (ASD) and, less often, a ventricular septal defect (VSD), although other cardiovascular malformations have been reported. The upper limb malformations most often affect the forearm and thumb. The thumb may be absent or it may be a nonopposable fingerlike digit. All gradations in defects in the upper limb and shoulder girdle have been reported.
Holt-Oram syndrome (heart-hand syndrome, cardiac-limb syndrome, atriodigital dysplasia):  A genetic syndrome characterized by the combination of heart disease and malformations of the upper limb. The heart defect is usually an atrial septal defect (ASD) and, less often, a ventricular septal defect (VSD), although other cardiovascular malformations have been reported. The upper limb malformations most often affect the forearm and thumb. The thumb may be absent or it may be a nonopposable fingerlike digit. All gradations in defects in the upper limb and shoulder girdle have been reported.
Holter monitor:  A type of portable heart monitor. The Holter monitor is a small portable electrocardiogram (ECG). The device is worn in a pouch around the neck or waist. It keeps a record of the heart rhythm, typically over a 24-hour period, while the patient keeps a diary recording their activities and any symptoms they may feel. The ECG recording is then correlated with the person's record of their activities and symptoms. The Holter monitor is useful for identifying disturbances which are sporadic and which are not readily identified with the usual resting electrocardiogram test.
Holter monitor:  A type of portable heart monitor. The Holter monitor is a small portable electrocardiogram (ECG). The device is worn in a pouch around the neck or waist. It keeps a record of the heart rhythm, typically over a 24-hour period, while the patient keeps a diary recording their activities and any symptoms they may feel. The ECG recording is then correlated with the person's record of their activities and symptoms. The Holter monitor is useful for identifying disturbances which are sporadic and which are not readily identified with the usual resting electrocardiogram test. The monitor is named after Norman Holter (1914-83), an American biophysicist, who invented it.
Homeobox gene:  A gene containing a short DNA sequence of about 180 base pairs referred to as a homeobox. Homeobox genes encode proteins that bind and regulate the expression of DNA in multicellular organisms. Homeoboxes are present in the genomes of many organisms from fruit flies to humans, and they appear to determine when particular groups of genes are expressed during embryonic development.
Homeobox gene:  A gene containing a short DNA sequence of about 180 base pairs referred to as a homeobox. Homeobox genes encode proteins that bind and regulate the expression of DNA in multicellular organisms. Homeoboxes are present in the genomes of many organisms from fruit flies to humans, and they appear to determine when particular groups of genes are expressed during embryonic development.
Homeopath:  A person who practices homeopathy.
Homeopathy:  A system of therapy invented by the German physician Samuel Hahnemann (1755-1843) in the late 18th and early 19th centuries and based on the concept that disease can be treated with drugs (in minute doses) thought capable of producing the same symptoms in healthy people as the disease itself. It was both refined and popularized by the American physician James Tyler Kent. Homeopathy is based on the theory that each naturally occurring element, plant, and mineral compound will, when ingested or applied, result in certain symptoms. Hahnemann believed that, by diluting these substances in a standardized manner, one could reach the true essence of that substance. Hahnemann described this process of dilution as "potentizing" (German: "potenziert") the substance. These dilute amounts could then be used to treat the very symptoms they were known to produce. Hahnemann and his students approached their treatments in a holistic way, meaning that the whole of the body and spirit is dealt with, not just the localized disease. Hahnemann himself spent extended periods of time with his patients, asking them questions that dealt not only with their particular symptoms or illness, but also with the details of their daily lives. It is also suggested that the gentle approach of homeopathy was a reaction to the violent forms of medicine of the day, which included techniques such as bleeding. According to homeopathy, symptoms are the body's way of fighting disease. Homeopathy teaches that symptoms are to be encouraged, by prescribing a "remedy" in minuscule doses that in large doses would produce the same symptoms seen in the patient. These remedies are meant to stimulate the immune system, helping to cure the illness.
Homeopathy:  A system of therapy based on the concept that disease can be treated with drugs (in minute doses) thought capable of producing the same symptoms in healthy people as the disease itself. Homeopathy was invented by the German physician Samuel Hahnemann (1755-1843) in the late 18th and early 19th centuries. It was both refined and popularized by the American physician James Tyler Kent. Homeopathy is based on the theory that each naturally occurring element, plant, and mineral compound will, when ingested or applied, result in certain symptoms. Hahnemann believed that, by diluting these substances in a standardized manner, one could reach the true essence of that substance. Hahnemann described this process of dilution as "potentizing" the substance. These dilute amounts could then be used to treat the very symptoms they were known to produce. Hahnemann and his students approached their treatments in a holistic way, meaning that the whole of the body and spirit is dealt with, not just the localized disease. According to homeopathy, symptoms are the body's way of fighting disease. Homeopathy teaches that symptoms are to be encouraged, by prescribing a "remedy" in minuscule doses that in large doses would produce the same symptoms seen in the patient. These remedies are meant to stimulate the immune system, helping to cure the illness.
Homeostasis:  A property of cells, tissues, and organisms that allows the maintenance and regulation of the stability and constancy needed to function properly. Homeostasis is a healthy state that is maintained by the constant adjustment of biochemical and physiological pathways. An example of homeostasis is the maintenance of a constant blood pressure in the human body through a series of fine adjustments in the normal range of function of the hormonal, neuromuscular, and cardiovascular systems. These adjustments allow the maintenance of blood pressure needed for body function despite environmental changes and changes in a person's activity level and position. Other homeostatic mechanisms, for example, permit the maintenance of body temperature within a narrow range.
Homeostasis:  A property of cells, tissues, and organisms that allows the maintenance and regulation of the stability and constancy needed to function properly. Homeostasis is a healthy state maintained by constant adjustment of biochemical and physiological pathways. An example of homeostasis is the maintenance of a constant blood pressure in the human body through a series of fine adjustments in the normal range of function of the hormonal, neuromuscular, and cardiovascular systems. These adjustments allow the maintenance of blood pressure needed for body function despite environmental changes and changes in a person's activity level and position. Other mechanism, for example, permit the maintenance of body temperature within a narrow range.
Homeotherm:  A homeotherm is a warm-blooded animal (such as man) as opposed to a poikilotherm (an organism such as a frog that is cold-blooded) and a stenotherm (a creature that can only survive only within a very narrow temperature range). Another term for us warm-blooded creatures is endotherm.
Homeotherm:  A warm-blooded animal (such as man). Another term for us warm-blooded creatures is endotherm. A homeotherm generates its own heat where as poikilotherms (such as reptiles) relies on the environment for warmth.
Homicide:   1. The killing of a person, by implication involving intention and/or responsibility due to actions. 2. Strictly speaking, the killing of a male human being. (Femicide is the equivalent term for the killing of a female human being.)
Homocysteine:  An amino acid produced by the body, usually as a byproduct of consuming meat. Homocysteine is made from another amino acid, methionine, and then in turn is converted into other amino acids. Elevated levels of homocysteine in the blood appear to make for an elevated risk of cardiovascular (heart and vessel) disease. Levels of homocysteine as low as 12 micromoles per liter of blood plasma have been found associated with an increased risk of heart attack, stroke, peripheral vascular disease and venous thromboembolism (blood clots in the veins). A homocysteine level of 15 micromoles or above has a heart attack rate three times as high as normal. Even a level of 12 micromoles can double the coronary risk. Homocysteine can damage blood vessels in several ways. It injures the cells that line arteries and stimulates the growth of smooth muscle cells. Homocysteine can also disrupt normal blood clotting mechanisms, increasing the risk of clots that can bring on a heart attack or stroke. Elevated levels of homocysteine also appear to increase the chance of Alzheimer's disease.
Homocysteine:  An amino acid produced by the body, usually as a byproduct of consuming meat. Homocysteine is made from another amino acid, methionine, and then in turn is converted into other amino acids. Elevated levels of homocysteine in the blood appear to make for an elevated risk of cardiovascular (heart and vessel) disease.
Homocystinuria:  A genetic disease due to an enzyme deficiency. Among other events, there is a buildup of the amino acid homocystine. Progressive mental retardation is common in untreated cases. The finding of vascular disease and premature arteriosclerosis in persons with homocystinuria led to the theory that homocystine may be a factor in heart disease.
Homocystinuria:  A genetic disease due to an enzyme deficiency. Among other events, there is a buildup of the amino acid homocystine. Progressive mental retardation is common in untreated cases. The finding of vascular disease and premature arteriosclerosis in persons with homocystinuria led to the theory that homocystine may be a factor in heart disease.
Homogentisate oxidase:  The enzyme encoded in the HGD gene. Mutation of HGD causes the genetic disease alkaptonuria. Homogentisate oxidase is also called Homogentisate 1,2-dioxygenase.
Homograft:  The transplant of an organ or tissue from one individual to another of the same species with a different genotype. A transplant from one person to another, but not an identical twin, is a homograft. Homografts account for many human transplants, including those from cadaveric, living related, and living unrelated donors. Called also an alloggraft.
Homolog (homologue):  One chromosome of a pair.
Homologous:  The relationship between two chromosomes that are paired and so are homologs of each other.
Homologous chromosomes:   A pair of chromosomes containing the same gene sequences, each derived from one parent.
Homosexual:  A person sexually attracted to persons of the same sex. Homosexuals include males (gays) and females (lesbians). Can also be used as an adjective.
Homosexuality:  Sexuality directed toward someone of the same sex.
Homosexuality 1:  An alleged gene for human male homosexuality, aka gay gene.
Homotrisomy:  Trisomy (occurance of three - normal is two) of the same chromosome. The occurrence of two children in the same family with trisomy 21 (Down's syndrome) is an instance of homotrisomy.
Homozygosity:  The state of possessing two identical forms of a particular gene, one inherited from each parent. For example, a girl who is homozygous for cystic fibrosis received the cystic fibrosis gene from both of her parents and therefore she has cystic fibrosis. In such a case the person with homozygosity can be refered to as a "homozygote." The normal condition is termed "heterozygosity."
Honey bee allergy:  Allergic reactions to stings of the honey bee (Apis mellifera). These reactions can include dizziness, itching, welts, massive swelling, trouble breathing, low blood pressure, shock, and even death. Treatment is with subcutaneous administration of epinephrin. A honey bee sting in a person allergic to honey bee sting is a medical emergency.
Honey bee genome:  The genetic complement of the honey bee (Apis mellifera). Its genome is relatively small -- about one-tenth the size of the human genome -- and contains about 300 million DNA base pairs. Sequencing of the bee genome began in 2003 and a draft of it was completed in 2004. The bee genome may also help understand the genetics of social behavior.
Hong Kong flu:  A pandemic of influenza A (H3N2) in 1968-69. This virus was first detected in Hong Kong in early 1968 and spread to the United States later that year. where it caused about 34,000 deaths, making it the mildest pandemic in the 20th century.
Hookworm:  An intestinal parasite that usually causes diarrhea or cramps. Heavy infestation with hookworm can be serious for newborns, children, pregnant women, and persons who are malnourished. Hookworm infections occur mainly in tropical and subtropical climates and affect about 1 billion people -- about one-fifth of the world's population. One of the most common species of hookworm, Ancylostoma duodenale, is found in southern Europe, northern Africa, northern Asia, and parts of South America. A second species, Necator americanus, was once widespread in the southeastern US early in the 20th century.
Hormone:  A chemical substance produced in the body that controls and regulates the activity of certain cells or organs. Many hormones are secreted by specialized glands such as the thyroid gland. Hormones are essential for every activity of daily living, including the processes of digestion, metabolism, growth, reproduction, and mood control. Many hormones, such as the neurotransmitters, are active in more than one physical process. Examples of hormones include aldosterone, antidiuretic hormone(ADH), cortisol, erythropoietin, estrogen, human chorionic gonadotropin (hCG), parathormone, progesterone, and testosterone. A hormone originally denoted a chemical made by a gland for export to another part of the body. Now a hormone is more broadly any chemical, irrespective of whether it is produced by a special gland or not, for export or domestic use, that "controls and regulates the activity of certain cells or organs.". The word "hormao" which means "I set in motion" or "I stir up" was used in ancient Greece to covey the "vital principle" of "getting the juices flowing."
Hormone therapy:  A form of treatment that takes advantage of the fact that certain cancers depend on hormones to grow. Hormone therapy may include giving hormones to the patient or decreasing the level of hormones in the body. This is not to be confused with orthomolecular hormone therapy, the use of naturally occurring hormones in anti-aging medicine.
Horner syndrome:  A complex of abnormal findings, namely sinking in of one eyeball, ipsilateral ptosis (drooping of the upper eyelid on the same side) and miosis (constriction of the pupil of that eye) together with anhidrosis (lack of sweating) and flushing of the affected side of the face. Due to paralysis of certain nerves (specifically, the cervical sympathetic nerves).
Horripilation:  Better known as goose bumps, a temporary local change in the skin when it becomes rougher due to erection of little muscles, as from cold, fear, or excitement. The chain of events leading to this skin change starts with a stimulus such as cold or fear. That stimulus causes a nerve discharge from the sympathetic nervous system, a portion of the autonomic (involuntary) nervous system. The nerve discharge causes contraction of little muscles called the arrectores pilorum (the hair erector muscles). Contraction of these muscles elevates the hair follicles above the rest of the skin. And it is these tiny elevations we perceive as goose bumps.
Hospice:  A program or facility that provides special care for people who are near the end of life and for their families. Hospice care can be provided at home, in a hospice or another freestanding facility, or within a hospital.
Hospice care:  Care designed to give supportive care to people in the final phase of a terminal illness and focus on comfort and quality of life, rather than cure. The goal is to enable patients to be comfortable and free of pain, so that they live each day as fully as possible. Aggressive methods of pain control may be used. Hospice programs generally are home-based, but they sometimes provide services away from home -- in freestanding facilities, in nursing homes, or within hospitals. The philosophy of hospice is to provide support for the patient's emotional, social, and spiritual needs as well as medical symptoms as part of treating the whole person
Hospital:  The word "hospital" comes from the Latin "hospes" which refers to either a visitor or the host who receives the visitor. From "hospes" came the Latin "hospitalia", an apartment for strangers or guests, and the medieval Latin "hospitale" and the Old French "hospital." It crossed the Channel in the 14th century and in England began a shift in the 15th century to mean a home for the elderly or infirm or a home for the down-and-out. "Hospital" only took on its modern meaning as "an institution where sick or injured are given medical or surgical care" in the 16th century. Other terms related to hospital include hospice, hospitality, hospitable, host, hostel and hotel.
Hospital code:  While there is no formal definition for a "Code," doctors often use the term as slang to refer to a patient in cardiopulmonary arrest, requiring a team of providers (sometimes called a "code team") to rush to the specific location and begin immediate resuscitative efforts.
Hospitalist:  A hospital-based general physician. Hospitalists assume the care of hospitalized patients in the place of patients' primary care physician. The term "hospitalist" was first introduced in 1996 to describe physicians who devote much of their professional time and focus to the care of hospitalized patients. In the most prevalent American model of hospitalist care, several doctors practice together as a group and work full-time caring for inpatients. Doctors specializing in intensive care have long taken care of patients admitted to the ICU by primary care doctors; geriatricians working in nursing homes have often admitted patients to the care of their hospital-based colleagues; etc.
Host: 1:  The organism from which a parasite obtains its nutrition and/or shelter (e.g. the tax payers are the host of the federal government). 2. An organism or cell culture in which a virus can replicate itself. 3. The transplant recipient of a tissue or organ graft.
Hot flashes:  Episodes experienced by many, but not all, women undergoing menopause. A hot flash is a feeling of warmth, sometimes associated with flushing that spreads over the body and sometimes followed by perspiration. Menstruating women in their 40's may have hot flashes, and hot flashes may last for a decade or more in some women. There is no way to predict when they will cease in a given woman. They decrease in frequency over time. The cause of hot flashes is not completely understood. Hot flashes may have more to do with fluctuation of hormone levels as opposed to low hormone levels per se. A simple experiment involving a rapid IV push of magnesium will induce hot flashes in anyone, including men. The sensation is one of literally "burning up." Therefore, naturally occurring hot flashes probably involve rapid movement of electrolytes across cell membranes.
House officer:  A resident physician and surgeon of a hospital (the "house") who is receives further training, usually in a medical or surgical specialty, while caring for patients under the direction of the attending staff.
House staff:  The resident physicians of a hospital who care for patients under the direction of the attending staff. House in this context refers to the hospital.
House surgeon:  Literally, a surgeon in the house, the house being the hospital. The meaning of the term house surgeon varies significantly from country to country.
Houseboat carbon monoxide poisoning:  The invisible and potentially lethal danger of carbon monoxide on houseboats. Carbon monoxide poisoning is a danger when gasoline-powered engines are run in enclosed spaces. Severe carbon monoxide poisoning can also occur outdoors, specifically with houseboats. From 1994 to 2004, there were more than 100 non-fatal carbon monoxide poisonings on houseboats in the US with at least 9 deaths. Studies indicate that houseboats with on-board electricity generators that vent toward the rear of the boat can pose a danger of carbon monoxide poisoning to people on the rear swim deck or water platform. Carbon monoxide poisonings have also occurred inside houseboats.
Housekeeping gene:  A gene involved in basic functions needed for the sustenance of the cell. Housekeeping genes are constitutively expressed (they are always turned ON).
Housemaid's knee (prepatellar bursitis, roofer's knee):   Inflammation of the bursa that is positioned in front of the kneecap (patella). Prepatellar bursitis commonly occurs as a result of repeated trauma to the knee such as from kneeling on hard surfaces in an occupation.
Hox gene:  One of a subgroup of homeobox genes that are found in clusters on the genes of vertebrates. These are referred to as Hox clusters in mammals. Hox clusters play a role in directing embryonic development.
Human chorionic gonadotropin (hCG):  A human hormone made by chorionic cells in the fetal part of the placenta. Human chorionic gonadotropin (hCG) is directed at the gonads and stimulates them. Hence, the name "gonadotropin." The presence of hCG is detectable by immunologic means within days of fertilization and forms the foundation of the common pregnancy tests. The level of hCG tends to be higher with a female fetus soon after conception. The level of hCG in maternal serum also enters as one component in the "double" and the "triple" screening tests used during pregnancy to assign risks of Down syndrome and other fetal disorders.
Human chromosome count:  The usual number of chromosomes in humans, 46 chromosomes. Also called the human chromosome complement.
Human embryonic stem cell:  Also known as a human pluripotent stem cell, one of the "cells that are self-replicating, are derived from human embryos or human fetal tissue, and are known to develop into cells and tissues of the three primary germ layers (ectoderm, mesoderm, and endoderm). Although human pluripotent stem cells may be derived from embryos or fetal tissue, such stem cells are not themselves embryos.
Human gene map:  The locations of the human genes. The location of each gene is called a locus (plural: loci).
Human herpesvirus 1 (HHV-1):  A herpes virus that causes cold sores and fever blisters in and around the mouth. In rare cases, as when the immune system is severely compromised, this virus can cause infection of the brain (encephalitis). HHV-1 is also known as herpes simplex type 1.
Human herpesvirus 2 (HHV-2):  A herpes virus that causes genital herpes, characterized by sores in the area of the genitalia. Genital herpes is a sexually transmitted disease (STD). This virus, like human herpesvirus 1, can cause infection of the brain (encephalitis) if the immune system is severely defective or compromised. The treatment of infection with human herpesvirus 2 is by topical or oral anti-viral medication. Human herpesvirus 2 (HHV-2) is also known as herpes simplex type 2.
Human herpesvirus 3:  See herpes zoster.
Human herpesvirus 4:  See Epstein-Barr virus.
Human herpesvirus 5:  See cytomegalovirus.
Human herpesvirus 6:  A herpes virus that apparently lies dormant in many people, human herpesvirus 6 is most likely to cause problems when the immune system is compromised by disease, as in AIDS patients, or by deliberate immune suppression, as in organ transplant patients. There are two forms of HHV-6, A and B. A is rare, and acquired in adulthood. B is relatively common, usually acquired in childhood, and associated with roseola. Both A and B can reactivate at a later date, and are believed to contribute to diseases of the bone marrow and/or central nervous system in some patients, including fatal encephalitis, chronic fatigue syndrome, and possibly multiple sclerosis. Diagnosis is by rapid blood culture or other blood test. Treatment is experimental at this time, but anti-viral drugs or beta interferon may be tried. Abbreviated HHV-6.
Human herpesvirus 7:  Closely related to HHV-6, human herpesvirus 7 has also been linked to roseola. Researchers believe it may also cause seizures and other central nervous system symptoms in children. Diagnosis is by rapid blood culture or other blood test. Treatment is experimental at this time, but anti-viral drugs or beta interferon may be tried. Abbreviated HHV-7.
Human herpesvirus 8:  A herpesvirus that contributes to the development of Kaposi sarcoma, an otherwise rare form of cancer sometimes seen in AIDS patients, and to some B-cell lymphomas. The predominant route of HHV-8 transmission is sexual. An additional route is via blood contact among injection drug users. Diagnosis is by rapid blood culture or another blood test. Treatment is experimental at this time, but anti-viral drugs or beta interferon may be tried. Human herpesvirus 8 (HHV-8) is also known as Kaposi sarcoma-associated herpesvirus, or KSHV. Abbreviated HHV-8.
Human immunodeficiency virus (HIV):  the major co-factor cause of AIDS. HIV has also been called the human lymphotropic virus type III, the lymphadenopathy-associated virus and the lymphadenopathy virus. No matter what name is applied, it is a retrovirus. A retrovirus has an RNA genome and a reverse transcriptase enzyme. Using the reverse transcriptase, the virus uses its RNA as a template for making complementary DNA which can integrate into the DNA of the host organism). The French physician Luc Montagnier (1932-) and his team at the Pasteur Institute discovered HIV in 1983- 84.
Human kinome:  A subset of the genome consisting of the protein kinase genes. The complete complement of over 500 protein kinases constitutes one of the largest of all human gene families. Protein kinases act as key regulators of cell function by catalyzing (facilitating) the addition of a negatively charged phosphate group to proteins. This process of protein phosphorylation, in turn, regulates protein function in both normal and disease states.
Human metapneumovirus:  A novel virus that is a ubiquitous and important agent of respiratory disease. The human metapneumovirus (hMPV) was discovered in 2001 in young children in The Netherlands with acute respiratory illnesses ranging from mild upper respiratory infections to severe bronchiolitis and pneumonia. It has since been found to cause severe acute respiratory infections all over the world in young children, the elderly, and people with weak defense systems (the immunocompromised). It accounts for 1 to 3% of all flu-like illnesses. (The influenza viruses, which belong to the orthomyxovirus family, cause most cases of flu and flu-like illnesses.) Although hMPV is a distinct and different virus from respiratory syncytial virus (RSV), it shares many features with RSV. For example, it tends to strike in the winter months in temperate climates.
Human papillomavirus (HPV):  A family of over 100 viruses including those which cause warts and are transmitted by contact. Some types of HPV are associated with tumors of the genital tract including, notably, cancer of the cervix. Of the more than 100 types of HPVs, over 30 types can be passed from one person to another through sexual contact. Most genital HPV infections come and go over the course of a few years. However, sometimes HPV infection may persist for many years, with or without causing cellular abnormalities. The majority of HPVs produce warts on the hands, fingers, and even the face. Most of these viruses are thus innocuous, causing nothing more than cosmetic concerns. HPVs also can cause painful plantar warts (on the sole of the foot). Several types of HPV, however, are confined primarily to the moist skin of the genitals, producing genital warts and markedly elevating the risk for cancer of the cervix.
Human parainfluenza virus:  One in a group of four RNA viruses that rank second only to respiratory syncytial virus (RSV) as a common cause of lower respiratory tract disease in young children. Like RSV, human parainfluenza viruses (HPIVs) can cause repeated infections throughout life. These infections are usually manifested by an upper respiratory tract illness (such as a cold or sore throat). HPIVs can also cause serious lower respiratory tract disease with repeat infection (including pneumonia, bronchitis, and bronchiolitis), especially among the elderly, and among patients with compromised immune systems.
Human pluripotent stem cell:  One of the "cells that are self-replicating, are derived from human embryos or human fetal tissue, and are known to develop into cells and tissues of the three primary germ layers. "Self-replicating" means the cell can divide and to form cells indistinguishable from it. The "three primary germ layers" -- called the ectoderm, mesoderm, and endoderm -- are the primary layers of cells in the embryo from which all tissues and organs develop. Human pluripotent stem cells are also known as human embryonic stem cells.
Human T-lymphotropic virus:  HTLV. A retrovirus that causes adult T-cell leukemia. HTLV is endemic (constantly present) in southern Japan and the Caribbean basin and occurs sporadically in Africa, Latin America, the Middle East, and the US. Adult T-cell leukemia occurs in less than 5% of people with HTLV infection, with an average latency period (a long delay) of more than 30 years. HTML can be transmitted by blood transfusions or tissue transplants. The virus is also known as human T-lymphotropic virus-I (HTLV-I).
Human T-lymphotropic virus type III:  An obsolete term for the human immunodeficiency virus, now commonly called HIV.
Humerus:  The long bone in the arm which extends from the shoulder to the elbow.
Humidifier fever:  A form of sick building syndrome that usually develops on the first workday of the week. The hallmark of the disease is the sudden onset of fever. Other features may include muscle aches and pains and mild shortness of breath. Humidifier fever can be caused by a number of different agents including amebas, bacteria, and fungi that may live in the moist environment of an humidifier. Humidifier fever typically resolves once the patient is no longer exposed to the causative agent coming from the humidifier.
Humor:  In medicine, humor refers to a fluid (or semifluid) substance. Thus, the aqueous humor is the fluid normally present in the front and rear chambers of the eye. The humors ran through an ancient theory that held that health came from balance between the bodily liquids. These liquids were termed humors. Disease arose when there was imbalance between these humors. The humors were: Phlegm (water), Blood, Gall (black bile thought to be secreted by the kidneys and spleen), and Choler (yellow bile secreted by the liver).
Humoral:  Pertaining to elements in the blood or other body fluids. In medicine, humor refers to a fluid (or semifluid) substance.
Hunter syndrome:  A genetic metabolic disorder that arises from deficiency of the enzyme iduronate sulfatase, resulting in tissue deposits of molecules called mucopolysaccharides. The characteristic features of Hunter syndrome include dwarfism, bone deformities, a thickened coarse face, hepatosplenomegaly (enlargement of the liver and spleen) from mucopolysaccharide deposits, cardiovascular disorders from mucopolysaccharide deposits, and deafness. There is no clouding of the cornea. There are two forms of Hunter syndrome. One is a severe form that causes progressive mental retardation, physical disability, and death before age 15 in most cases. The other is a mild form that is compatible with survival to adulthood and reproduction and in which the intellect is impaired minimally, if at all. Both forms of Hunter syndrome are inherited in an X-linked recessive manner. The gene for iduronate sulfatase is on the X chromosome. Bone marrow transplantation has been done without consistently encouraging results. Iduronate sulfatase is currently being tested in enzyme replacement therapy. Hunter syndrome is also known as mucopolysaccharidosis.
Huntington disease:  An hereditary disorder with mental and physical deterioration leading to death. Although characterized as an "adult-onset" disease, it can affect children as well. Huntington disease describes an autosomal dominant pattern of inheritance with high penetrance (a high proportion of persons with the gene develop the disease). The characteristic findings of Huntington disease are caused by loss of neurons (nerve cells) in the brain. The Huntington disease gene codes for a protein that has been named (confusingly) huntingtin whose function is unknown. The degree of elongation of the huntingtin protein appears to correlate with the loss of neurons in the disease. Mood disturbance is usually the first symptom seen, with bipolar disorder-like mood swings that may include mania, depression, extreme irritability or angry outbursts, and psychosis. Other symptoms include chorea (restless, wiggling, turning movements), muscle stiffness and slowness of movement, and difficulties with memory and other cognitive processes. The HD gene is located on chromosome 4, and is an autosomal dominant gene. Only one copy need be inherited to cause the illness. Diagnosis is by genetic testing, and family members of people with Huntington's disease may also want to know if they carry the HD gene. At this time, there is no cure for HD, although medication may be used to control symptoms of the illness, such as mood swings and chorea.
Hurler syndrome:  An inherited error of metabolism in which there is deficiency of the enzyme alpha-L-iduronidase which normally breaks down molecules called mucopolysaccharides. Without the activity of this enzyme, there is an abnormal accumulation of mucopolysaccharides in the tissues of the body. There are 2 clinical subtypes of disease due to deficiency of alpha-L-iduronidase: Hurler syndrome and Scheie syndrome. Hurler syndrome patients have progressive mental retardation, gross facial features, enlarged and deformed skull, small stature, corneal opacities, hepatosplenomegaly (enlargement of the liver and spleen), valvular heart defects, thick skin, joint contractures, and hernias.
Hyaline membrane disease:  A respiratory disease of the newborn, especially the premature infant, in which a membrane composed of proteins and dead cells lines the alveoli (the tiny air sacs in the lung), making gas exchange difficult or impossible. The word "hyaline" comes from the Greek word "hyalos" meaning "glass or transparent stone such as crystal." The membrane in hyaline membrane disease looks glassy. Hyaline membrane is now commonly called respiratory distress syndrome (RDS). It is caused by a deficiency of a molecule called surfactant. RDS almost always occurs in newborns born before 37 weeks of gestation. The more premature the baby is, the greater is the chance of developing RDS. RDS is more likely to occur in newborns of diabetic mothers.
Hyaluronic acid:  A viscous slippery substance that lubricates the joints, maintains the shape of the eyeballs, and is a key component of connective tissue.
Hybrid:  The word "hybrid" has a number of different biomedical meanings. In transmission genetics, a hybrid is the result of a cross between two genetically dissimilar parents. The offspring of unlike parents. If the parents are sufficiently dissimilar, the hybrid may be sterile (for example, in the crossing of horse and donkey to produce a mule). In cell genetics, a hybrid cell is one that contains components from one or more genomes (other than zygotes and their derivatives). Hybrid cells may be formed by several techniques including cell fusion, the fusion of two or more cells. In molecular genetics, a hybrid DNA molecule is a DNA molecule with strands of different origin.
Hybridoma:  A cell hybrid resulting from the fusion of a cancer cell and a normal lymphocyte (a type of white blood cell). The hybridoma is immortal in the laboratory and makes the same products as its parent cells forever.
Hydatid disease, alveolar:  A parasitic disease caused by the larval stage of a microscopic tapeworm called Echinococcus multilocularis.
Hydatidiform mole:  A tumor that forms in the uterus as a mass of cysts resembling a bunch of grapes. Moles occur during the childbearing years. They do not spread outside of the uterus. However, a malignancy called choriocarcinoma may start from a hydatidiform mole.
Hydranencephaly:  A condition in which the cerebral hemispheres of the brain are absent and replaced by sacs filled with cerebrospinal fluid. Usually the cerebellum and brainstem are formed normally. An infant with hydranencephaly may appear normal at birth. The infant's head size and spontaneous reflexes such as sucking, swallowing, crying, and moving the arms and legs may all seem normal. However, after a few weeks the infant usually becomes irritable and has increased muscle tone (hypertonia). After several months of life, seizures and hydrocephalus may develop.
Hydrazine sulfate:  An alternative medicine that has been claimed to be a treatment for cancer. It has been used as a first-line agent in cancer therapy and as a treatment for cancer-related anorexia (loss of appetite) and cachexia (loss of muscle mass and body weight). The results from a scientific standpoint have been inconclusive. The substance is not without possible adverse effects. At least one death has been laid to it.
Hydrocele:  Accumulation of fluid in the coat around the testis. Small hydroceles tend to disappear by a year of age while larger hydroceles may persist and warrant surgery.
Hydrocephalus (aka hydrocephaly):  Hydrocephalus is an abnormal buildup of cerebrospinal fluid (CSF) in the ventricles of the brain. The fluid is often under increased pressure and can compress and damage the brain. Hydrocephalus can arise before birth or any time afterward. It may be due to many causes including a birth defect, hemorrhage into the brain, infection, meningitis, tumor, or head injury. Most forms of hydrocephalus are the result of obstructed CSF flow in the ventricular system. With birth defects, physical obstruction of CSF flow in the ventricular system is usually the cause of the hydrocephalus. Hydrocephalus is a common companion of spina bifida (meningomyelocele).
Hydrocephalus ex-vacuo:  What is termed "hydrocephalus ex-vacuo" occurs when there is damage to the brain caused by stroke or injury, and there may be an actual shrinkage of brain substance. Although there is more CSF than usual, the CSF pressure itself is normal in hydrocephalus ex-vacuo.
Hydrocephalus, acquired:  Hydrocephalus due to a postnatal cause, something that happened sometime after birth.
Hydrocephalus, communicating:  Hydrocephalus in which there is no obstruction to the flow of the cerebrospinal fluid (CSF). Specifically, there is no obstruction within the ventricular system of the brain or where the CSF passes into the spinal canal. By process of elimination, the hydrocephalus is due to overproduction of CSF or failure of the brain to reabsorb CSF normally.
Hydrocephalus, congenital:  Hydrocephalus present at birth.
Hydrocephalus, Macewen sign of:  A sign to detect hydrocephalus (and brain abscess). Percussion (tapping) on the skull at a particular spot (near the junction of the frontal, temporal and parietal bones) yields an unusually resonant sound in the presence of hydrocephalus or a brain abscess. Named for Sir William Macewen (1848-1924), a surgeon in Glascow, Scotland who also described Macewen's operation for inguinal hernia.
Hydrocephalus, normal pressure:  A specific form of hydrocephalus in which the central cavities of the inner brain (the ventricles) enlarge at the expense of the substance of the brain, while the pressure of the CSF remains within normal range. Normal pressure hydrocephalus (NPH) is due usually to a gradual blockage of the drainage pathways for cerebrospinal fluid (CSF) in the brain. NPH can occur as a complication of brain infection or hemorrhage. In some patients no predisposing cause can be identified.
Hydrogen:  The most plentiful element in the universe and one present in all organic compounds. Hydrogen is a gas with an atomic number of 1 and the symbol H. Two isotopes of hydrogen -- deuterium and tritium -- have been used as tracers in metabolic studies. Tritium is a long-lived weak emitter of radiation and can be easily incorporated in large molecules such as DNA, and is therefore much used for autoradiography in the laboratory. Antoine Lavoisier coined the name hydrogen from the Greek hydro (water) + genes (forming), reflecting the fact that water is generated by the combustion of this element.
Hydronephrosis:  Distention of the kidney with urine. Due to obstruction of urine outflow (for example, by a stone blocking the ureter, the tube going from the kidney to the bladder).
Hydrophobia:  1. Literally, an irrational fear of water, to drink or to swim in. Someone who is scared of the water is hydrophobic. 2. A term once commonly used for rabies because in the later stages of that disease, the animal (or person) has difficulty swallowing and so fears a drink of water.
Hydrops fetalis:  Gross edema (swelling), usually with anemia, of the fetus. It can be due to Rh blood group incompatibility, in which antibodies crossing the placenta from the mother destroy the red blood cells of the fetus. It can also be caused by a lethal form of the genetic disorder thalassemia, alpha thalassemia, in which alpha-chain polypeptides needed to make fetal or adult hemoglobin are not produced.
Hydrosytryptamine (aka serotonin):  A hormone in the pineal gland, blood platelets, digestive tract, and the brain. Serotonin acts both as a chemical messenger that transmits nerve signals between nerve cells and that causes blood vessels to narrow.
Hydroxyapatite:  A major component and an essential ingredient of normal bone and teeth. Hydroxyapatite makes up bone mineral and the matrix of teeth. It is hydroxyapatite that gives bones and teeth their rigidity.
Hydroxyapatite crystal disease:  The inflammation caused by hydroxyapatite crystals has been referred to as hydroxyapatite crystal disease. Hydroxyapatite is a major component and an essential ingredient of normal bone and teeth, makes up bone mineral and the matrix of teeth, and gives bones and teeth their rigidity. Hydroxyapatite molecules can group together (crystalize) to form microscopic clumps. If these tiny crystals of hydroxyapatite are deposited by mistake in or around joints, they may cause inflammation of the joints and nearby tissues such as the tendons and ligaments (particularly causing rotator cuff problems in the shoulder) and this is hydroxyapatite crystal disease.
Hydroxyurea:  A drug that inhibits the synthesis of DNA and so is classified as an antimetabolite. Hydroxyurea is used to treat a number of diseases, including chronic myeloid leukemia (CML), polycythemia vera, carcinoma of the head and neck, ovary, and cervix, melanoma, and sickle cell disease. Hydroxyurea is taken orally and is inexpensive.
Hygiene:  The science of preventive medicine and the preservation of health. From the name of Hygeia, the daughter of Asklepios, the Greek god of medicine (whose staff with entwined snake is the symbol of medicine). Asklepios (known to the Romans as Aesculapius) had a number of children including not only Hygeia but also Panaceia, the patroness of clinical medicine. Hygeia followed her father into medicine. As the patroness of health, Hygeia was charged with providing a healthy environment to prevent illness. In Greek, "hygieia" means health.
Hygiene hypothesis (aka hygiene theory):  A hypothesis that states that exposure to allergens in the environment early in life reduces the risk of developing allergies by boosting immune system activity. Conversely, relatively clean environment in early life would sway the immune system towards allergy-promoting responses. Also called the hygiene theory. The hygiene hypothesis may explain the rising incidence of allergic diseases and facts such as the following: the lower incidence of allergy in those living on farms or in rural areas (due possibly to more exposure to bacteria in barns and elsewhere in the country); the lower incidence of allergy in younger children of large families with 3 or more older siblings (due perhaps to repeated exposure to infection from older siblings); and the lower incidence of asthma and wheezing in children who go to day care centers (where they are exposed to more infections). The hygiene hypothesis, however, cannot explain the higher rates of allergic asthma among poor African Americans in the inner city areas.
Hymen:  A thin membrane which completely or partially occludes the vaginal opening. The hymen is a fold of mucous membrane usually present at birth at the orifice of the vagina. It is also called the vaginal membrane (or, sometimes, the virginal membrane).
Hyoglossus:  The muscle that permits the tongue to be held on the floor of the mouth.
Hyper-:  Prefix meaning "high, beyond, excessive, above normal" as in hypercalcemia (high calcium in the blood) and hypersensitivity. The opposite of hyper- is hypo-.
Hyper-IgD syndrome:  A genetic disorder characterized by recurring attacks of chills and fever that usually start before the first birthday and last for 4 to 6 days, usually accompanied by swollen glands in the neck and abdominal pain with vomiting or diarrhea. Other symptoms may include headache, joint pain (arthralgia), arthritis of the large joints, and reddish spots (macules) and bumps (papules) on the skin, and bleeding (petechiae and purpura) into the skin. The attacks can be triggered by minor trauma, surgery, vaccination or stress. Patients may be free of attacks for months or even years. The key laboratory abnormality is a continuously high level of IgD (immunoglobulin D).
Hyperactivity:  A higher than normal level of activity. An organ can be described as hyperactive if it is more active than usual. Behavior can also be hyperactive. People who are hyperactive always seem to be in motion. They can't sit still; they may dash around or talk incessantly. Sitting still through a lesson can be an impossible task. They may roam around the room, squirm in their seats, wiggle their feet, touch everything, or noisily tap a pencil. They may also feel intensely restless.
Hyperadrenocorticism:  Excess hormone called "cortisol". Often called Cushing's syndrome, it is an extremely complex condition that involves many areas of the body. It results from an excess of cortisol and its effects on the human body. Common symptoms are thinning of the skin, weakness, weight gain, bruising, hypertension, diabetes, weak bones (osteoporosis), facial puffiness, and in women cessation of periods.
Hyperaldosteronism:  Overproduction of the hormone aldosterone from the outer portion (cortex) of the adrenal gland or a tumor containing that type of tissue. Excess aldosterone (pronounced al-do-ster-one or al-dos-ster-own) results in low potassium levels (hypokalemia), underacidity of the body (alkalosis), muscle weakness, excess thirst (polydipsia), excess urination (polyuria), and high blood pressure (hypertension). AKA aldosteronism and Conn's syndrome.
Hyperbaric:  Pertaining to gas pressures greater than 1 atmosphere* of pressure. Also pertaining to solutions that are more dense than the medium to which they are added. The term "hyperbaric" is derived from Greek roots: "hyper-" meaning high, beyond, excessive, above normal + "baros" meaning weight. Hyperbaric oxygenation is an increased amount of oxygen in organs and tissues resulting from the administration of oxygen in a compression chamber at an ambient pressure greater than 1 atmosphere* of pressure.
Hyperbilirubinemia:  An elevated level of the pigment bilirubin in the blood. A sufficient elevation will produce jaundice. Some degree of hyperbilirubinemia is very common in babies right after birth, especially premies.
Hyperbilirubinemia type I:  Better known as Gilbert's disease, a common but harmless genetic condition in which a liver enzyme essential to the disposal of bilirubin (the chemical that results from the normal breakdown of hemoglobin from red blood cells) is abnormal. (The errant enzyme is called UDP- glucuronosyltransferase). This enzyme abnormality results in mild elevation of bilirubin pigment in the blood and the elevated bilirubin pigment, in turn, can sometimes cause mild yellowing (jaundice) of the eyes. People with Gilbert's disease are otherwise entirely normal with no other signs or symptoms and their liver enzymes in blood serum are also entirely normal.
Hyperbilirubinemia, neonatal:  Elevation of the bilirubin level in the blood of the newborn, which results in yellowish staining of the skin and whites of the newborn's eyes (sclerae) by pigment of bile (bilirubin). In newborn babies a degree of jaundice is normal. It is due to the breakdown of red blood cells (which release bilirubin into the blood) and to the immaturity of the newborn's liver (which cannot effectively metabolize the bilirubin and prepare it for excretion into the urine). Normal neonatal jaundice typically appears between the 2nd and 5th days of life and clears with time. Neonatal hyperbilirubinemia is also referred to as neonatal jaundice and physiologic jaundice of the newborn.
Hypercalcemia:  A higher-than-normal level of calcium in the blood. This can cause a number of nonspecific symptoms, including loss of appetite, nausea, thirst, fatigue, muscle weakness, restlessness, and confusion. Excessive intake of calcium may cause muscle weakness and constipation, affect the conduction of electrical impulses in the heart (heart block), lead to calcium stones (nephrocalcinosis) in the urinary tract, impair kidney function, and interfere with the absorption of iron predisposing to iron deficiency. According to the National Academy of Sciences, adequate intake of calcium is 1 gram daily for both men and women. The upper limit for calcium intake is 2.5 grams daily.
Hypercalciuria:  Excess calcium in the urine.
Hypercapnia:  More than the normal level of carbon dioxide in the blood. Hypercapnia is as opposed to hypocapnia and acapnia. The origin of the suffix "-capnia" is curious. It comes from the Greek "kapnos" referring to carbon dioxide which is a principal part of smoke.
Hypercarbia:  More than the normal level of carbon dioxide in the blood. Hypercarbia is the opposite of hypocarbia
Hyperchloremia:  Elevated blood levels of chloride. Chloride is the major anion found in the fluid outside of cells and in blood. An anion is the negatively charged part of certain substances such as table salt (NaCl) when dissolved in liquid. Sea water has almost the same concentration of chloride ion as human fluids. The balance of chloride ion (Cl-) is closely regulated by the body. Significant increases or decreases in chloride can have deleterious or even fatal consequences. Increased chloride (hyperchloremia): Elevations in chloride may be seen in diarrhea, certain kidney diseases, and sometimes in overactivity of the parathyroid glands.
Hypercholesterolemia:  High blood cholesterol. This can be sporadic (with no family history) or familial. Familial hypercholesterolemia is the most common inherited type of hyperlipidemia (high lipid levels in blood). It predisposes to premature arteriosclerosis including coronary artery disease with heart attacks at an unusually young age. About half of men and a third of women suffer a heart attack by age 60. Familial hypercholesterolemia manifests cholesterol levels of 400 and up. Persons with familial hypercholesterolemia can reduce their risk by adhering to a very low cholesterol diet under a doctor's supervision, and may also need to take medications that reduce their cholesterol level. Familial hypercholesterolemia is recognizable in childhood. Children and other relatives at risk for familial hypercholesterolemia can be screened (checked) for the condition. Familial hypercholesterolemia is due to a genetic defect in the receptor (the dock on the surface of cells) for LDL (low density lipoprotein).
Hypercoagulability state:  An abnormally increased tendency toward blood clotting (coagulation). There are numerous hypercoagulable states. Each has different causes and each increases a person's chances of developing blood clots such as those associated with thrombophlebitis (clot in the veins). Causes of hypercoagulable states include medications (female hormones, estrogens and birth control pills), after surgery (post- operative period, especially hip, knee, and urinary system procedures), pregnancy, phospholipid antibodies in blood (anticardiolipin antibodies, lupus anticoagulant), cancer (though most patients with a hypercoagulable state do not have cancer), elevated blood homocysteine levels, and inherited protein deficiencies (antithrombin III, factor V Leiden, protein S, protein C, and others).
Hypercoagulability state, estrogen-associated:  A supranormal tendency for blood to clot which occurs as an occasional but serious side effect of estrogen therapy. The blood clots in this situation are dose-related, that is they occur more frequently with higher doses of estrogen. Estrogen therapy preparations (all of which carry this risk) include: esterified estrogens, esterified estrogens combined with methyltestosterone, estradiol, conjugated estrogens combined with medroxyprogesterone, and conjugated estrogens. The brand names of the estrogen therapy preparations carrying this risk include: CLIMARA (estradiol), ESTRACE (estradiol), ESTRADERM (estradiol), ESTRATAB (esterified estrogens), ESTRATEST (esterified estrogens and methyltestosterone), MENEST (esterified estrogens), OGEN (estropipate), PREMARIN (estrogens conjugated), PREMPHASE (estrogens conjugated and medroxyprogesterone), PREMPRO (estrogens conjugated and medroxyprogesterone), cigarette smokers on estrogen therapy are at a higher risk than non-smokers for blood clots. Therefore, patients requiring estrogen therapy are strongly encouraged to quit smoking.
Hyperekplexia:  A genetic disorder also known as hyperexplexia in which babies have an exaggerated startle reflex (reaction). Additional findings include a tendency to umbilical and inguinal hernias (presumably due to increased intra-abdominal pressure) and congenital dislocation of the hip. The exaggerated startle response persists throughout life; startles can be elicited by lightly touching the person's nose, clapping or making other noises, or suddenly jolting the person's chair. The gene responsible for this disease has been found on chromosome number 5. Treatment is with medications. The neurologic features can usually be controlled with clonazepam (KLONOPIN). In some cases, phenobarbital, diazepam (VALIUM), and valproic acid (DEPAKENE) have also been found useful. Hyperexplexia is also called Kok disease, startle disease, exaggerated startle reflex, and stiff baby syndrome.
Hyperemesis gravidarum:  Excessive vomiting in early pregnancy. Hyperemesis gravidarum, by definition, leads to the loss of 5% or more of the body weight of the woman. Hyperemesis gravidarum affects about one in every 300 pregnant women. It is more common in young women, in first pregnancies and in women with multiple pregnancies (twins, triplets, etc.) Hyperemesis gravidarum is usually self-limited (stops on its own) and, although very inconvenient and very discomforting, it is usually of little clinical consequence. However, sometimes hyperemesis can keep the mother from getting the necessary fluids and nutrition.
Hyperexplexia:  see hyperekplexia above.
Hyperextensible:  Unusually capable of being extended and stretched. Hyperextensible skin is a feature of Ehlers-Danlos syndrome.
Hyperglycemia:  A high blood sugar. An elevated level specifically of the sugar glucose in the blood. Hyperglycemia is often found in diabetes mellitus. It occurs when the body does not have enough insulin or cannot use the insulin it has to turn glucose into energy. Hyperglycemia may also occur in Cushing's syndrome and other conditions. The signs of hyperglycemia are polydipsia (a great thirst), polyuria (a need to urinate often), and a dry mouth.
Hypergraphia:  The driving compulsion to write; the overwhelming urge to write. Hypergraphia may compel someone to keep a voluminous journal, to jot off frequent letters to the editor, to write on toilet paper if nothing else is available, and perhaps even to compile a dictionary. Hypergraphia is the opposite of writer's block. Temporal lobe epilepsy is associated with hypergraphia.
Hyperhidrosis:  Excessive sweating. Hidrosis meaning sweating, so hyperhidrosis is too much sweating.
Hyperkalemia:  Elevated blood potassium. Potassium is the major positive ion (cation) found inside of cells. The chemical notation for potassium is K+. The proper level of potassium is essential for normal cell function. An abnormal increase (or decrease) of potassium can profoundly affect the nervous system and heart, and when extreme, can be fatal. The normal blood potassium level is 3.5 - 5.0 milliEquivalents/liter (mEq/L), or in international units, 3.5 - 5.0 millimoles/liter (mmol/L). IV injection of large amounts of postassium chloride is a common adjunct in death by lethal injection. This stops the heart.
Hyperlexia:  The presence of advanced ability to read compared to the ability to understand spoken language. Children with hyperlexia have a precocious ability to read words, far above what would be expected at their chronological age or an intense fascination with letters or numbers; significant difficulty in understanding verbal language; and abnormal social skills, difficulty in socializing and interacting appropriately with people. Hyperlexia may belong in the autistic spectrum along with autism and Asperger syndrome.
Hyperlipidemia:  High lipid (fat) levels in the blood.
Hypermagnesemia:  Excess magnesium. Persons with impaired kidney function should be especially careful about their magnesium intake because they can accumulate magnesium, a dangerous (and sometimes fatal) situation.
Hypermnesia:  Abnormally strong memory of the past.
Hypermobility syndrome:  A common benign childhood condition involving hypermobile joints (that can move beyond the normal range of motion). Symptoms include pains in knees, fingers, hips, and elbows. The affected joints may sprain or dislocate. Scoliosis (curvature of the spine) is more frequent. Usually improves with adulthood. Also called the joint hypermobility syndrome.
Hypernatremia:  Elevated blood sodium. Sodium is the major positive ion (cation) in fluid outside of cells. The chemical notation for sodium is Na+ (from natrium, Latin for sodium). When combined with chloride (Cl), the resulting substance is table salt (NaCl). (Actually most table salt is 80% sodium iodide, but we continue to think of table salt as NaCl). Excess sodium (such as from fast food and processed food) is excreted in the urine. Too much (or too little) sodium can cause cells to malfunction, and extremes can be fatal. In people with hypertension, table salt magnifies the disorder. Mormal blood sodium level is 135 - 145 milliEquivalents/liter (mEq/L), or in international units, 135 - 145 millimoles/liter (mmol/L).
Hyperopia:  Farsightedness; the ability to see distant objects more clearly than close objects; correctible with a "+" (convex) lens.
Hyperostosis:  Overgrowth of bone. Hyperostosis is a nonspecific term that does not refer to any particular condition.
Hyperoxaluria:  An hereditary disorder that causes a special type of stone to form in the kidney and the urine beginning in childhood. Also known as oxalosis.
Hyperparathyroidism:  Too much parathyroid hormone (parathormone) resulting in abnormally high levels of calcium in the blood (hypercalcemia).
Hyperphosphatemia:  A higher than normal blood level of phosphate. Phosphate molecules are particularly important as part of larger molecules in cell energy cycles. Higher than normal levels can be caused by ingestion of phosphate-rich foods, such as dairy products, or by kidney failure.
Hyperpigmentation:  Dark spots on the skin. Hyperpigmentation is primarily a cosmetic concern that can be covered with make-up, although in some cases (such as the cafe au lait spots associated with neurofibromatosis) it can be a sign of an underlying medical problem. If treatment of hyperpigmentation is desired, a dermatologist may be able to use dermabrasion, laser treatments, or bleaching agents to effect change.
Hyperplasia:  A condition in which there is an increase in the number of normal cells in a tissue or organ.
Hypertension:  High blood pressure, defined as a repeatedly elevated blood pressure exceeding 140 over 90 mmHg -- a systolic pressure above 140 with a diastolic pressure above 90. Chronic hypertension is a "silent" condition. Stealthy as a cat, it can cause blood vessel changes in the back of the eye (retina), abnormal thickening of the heart muscle, kidney failure, and brain damage. For diagnosis, there is no substitute for measurement of blood pressure. No specific cause for hypertension is found in 95% of cases. Hypertension is treated with regular aerobic exercise, weight reduction (if overweight), salt restriction, and medications. The incidence of hypertension increases with age. It is the most common medical disorder seen in America today. In my practice, more than 50% of adults (all ages) have unsuspected hypertension. Most are stress-induced and are written off with this excuse by many doctors. However, life is full of stress and these people are therefore in medical danger.
Hypertensive crisis:  A severe and potentially life-threatening increase in blood pressure . A hypertensive crisis is a medical emergency. When the blood pressure rises to levels of 180/110 or greater, the blood vessels and organs may become damaged. This damage can be manifested as a number of conditions including stroke, heart attack, pulmonary edema (fluid in the lungs), a tear in the main artery of the body, the aorta (known as an aortic dissection), and eclampsia (during pregnancy). Symptoms of a hypertensive crisis can include the symptoms typical for a stroke or heart attack; difficulty breathing, changes in mental status, and severe headache may also occur. Immediate medical attention is required for a severe increase in blood pressure. Treatment can involve hospitalization and the use of oral and/or intravenous medications.
Hyperthermia:  Overheating of the body. This may be due to extreme weather conditions. Unrelieved hyperthermia can lead to collapse and death, particularly in the elderly. Malignant hyperthermia is caused by a reaction to anesthesia. The body's metabolism rises suddenly, causing a sudden jump in body temperature and muscle rigidity. The result can be damage to tissues and organs (including the brain), or death. The propensity to malignant hyperthermia is inherited. Treatment is by administering dantrolene sodium (brand name: Dantrium) and rapidly cooling the patient.
Hyperthyroid:  Excess of thyroid hormone resulting from an overactive thyroid gland (or taking too much thyroid hormone). Symptoms can include increased heart rate, weight loss, depression, and cognitive slowing. Treatment is by medication, the use of radioactive iodine, thyroid surgery, or reducing the dose of thyroid hormone.
Hypertonia:  Increased tightness of muscle tone. Untreated hypertonia can lead to loss of function and deformity. Treatment is by physical and/or occupational therapy, and in some cases muscle relaxant medication. Injections of botulism toxin (botox) are a recent treatment for chronic hypertonia in cerebral palsy and other disorders. Also known as spasticity.
Hypertonic solution:  A solution with a higher salt concentration than in normal cells of the body and the blood.
Hypertrophic:  Exhibiting hypertrophy (enlargement or overgrowth of an organ or part of the body due to increased size of the constituent cells), as in hypertrophic cardiomyopathy.
Hypertrophic cardiomyopathy:  A genetic disorder of the heart characterized by increased thickness (hypertrophy) of the wall of the left ventricle, the largest of the four chambers of the heart. The disease can present at any time in life. It is the leading cause of sudden death in athletes and young people. Abbreviated HCM. It is inherited in an autosomal dominant manner. Men and women with HCM stand a 50-50 chance of transmitting the HCM gene to each of their children. Measurement of the thickness of the left ventricle wall can predict who is most at risk for HMC. The test is done by echocardiography, a routine ultrasound test of the heart. Persons with a maximum wall thickness less than three-quarters of an inch (19 mm) are virtually free of risk for fatal cardiac arrest over the next 20 years whereas those with a wall thickness more than 1.2 inches (30 mm) have a 40% chance of fatal cardiac arrest during that time period. Patients in danger can be fitted with implantable defibrillators. Also called familial hypertrophic cardiomyopathy.
Hypertrophic gastritis (aka hypertrophic hypoproteinemic gastropathy):  A premalignant disorder of the stomach characterized by overgrowth of the stomach lining (the gastric mucosa) and hypoalbuminemia (low blood serum level of albumin) due to loss of albumin by the stomach. The abnormalities of the stomach are highly characteristic with giant folds, excess mucus secretion by the lining of the stomach, and hypochlorhydria (decreased acid secretion by the stomach). The disease tends to lead to stomach cancer. Symptoms include nausea, vomiting, pain in the abdomen, swelling, poor appetite, and weight loss. The cause of the disease is not known, although infections with cytomegalovirus and Helicobacter pylori have been suspected to play a role. In some families, siblings have had the disease, due possibly to autosomal recessive inheritance.
Hypertrophy:  Enlargement or overgrowth of an organ or part of the body due to the increased size of the constituent cells. Hypertrophy occurs in the biceps and heart because of increased work. Cardiac hypertrophy is recognizable microscopically by the increased size of the cells. The term hypertrophy is applied to the enlargement of the uterus during pregnancy. The term benign prostatic hypertrophy is a misnomer because the increased size of the prostate is due to hyperplasia, an increase in the number of cells.
Hyperuricemia:  Abnormally elevated blood level of uric acid. Uric acid is a breakdown product of purines that are part of many foods we eat. While hyperuricemia may indicate an increased risk of gout , the relationship between hyperuricemia and gout is unclear. Many patients with hyperuricemia do not develop gout, while some patients with repeated gout attacks have normal or low blood uric acid levels. Among the male population in the United States, approximately ten percent have hyperuricemia. However, only a small portion of those with hyperuricemia will actually develop gout.
Hyperventilation:  Overbreathing. This can cause dizziness, lightheadedness, weakness, shortness of breath, a sense of unsteadiness, muscle spasms in the hands and feet, and tingling around the mouth and fingertips. All of these symptoms are the result of abnormally low levels of carbon dioxide in the blood caused by overbreathing.
Hypervolemia:   An abnormal increase in blood volume or, strictly speaking, an abnormal increase in the volume of blood plasma
Hypnagogic:  Concerning the drowsiness one commonly feels before sleep, the transitional state preceding sleep, and also the dream-like hallucinations that may occur at that time.
Hypnagogic hallucination:  A vivid dream-like hallucination that occurs as one is falling asleep. The opposite of an hypnopompic hallucination which is a vivid dreamlike hallucination that occurs as one is waking up.
Hypnic:  1. Inducing sleep. 2. Pertaining to sleep. A hypnic jerk is a sleep start or jerk. From the Greek hypnikos, from the Greek hypnos, sleep.
Hypnic headache:  A relatively rare form of headache disorder in which the patient is awakened from sleep nightly, usually between 1 and 3am, with intense dull or throbbing pain over the whole head. Each episode may last up to 1 hour and be associated with nausea. Similar episodes may occasionally strike in the daytime. Hypnic headache almost always affects people over 65.
Hypnic jerk:  The common normal phenomenon of jerking awake, usually accompanied by a feeling of falling, just as one is drifting off to sleep. Also called a sleep jerk or sleep start.
Hypnolepsy:  A neurological disorder marked by a sudden recurrent uncontrollable compulsion to sleep. Also known as narcolepsy.
Hypnopompic hallucination:   A vivid dreamlike hallucination that occurs as one is waking up. The opposite of an hypnagogic hallucination, which occurs as one is falling asleep.
Hypnos:  The Greek and Roman god of sleep. From his name is derived the term hypnosis. Hypnos was the twin of Thanatos, the personification of death. Both Hypnos and Thanatos lived in the underworld.
Hypo:  Prefix meaning "low, under, beneath, down, below normal" as in hypocalcemia (low calcium in the blood), hypoglycemia (low blood sugar) and hyposensitivity. The opposite of hypo- is hyper-.
Hypoalbuminemia:  An abnormally low blood level of albumin. Normally, albumin is the most plentiful protein in human blood and the key to the regulation of its osmotic pressure.
Hypocalcemia:  Lower-than-normal blood calcium. Low blood calcium makes the nervous system highly irritable with tetany (spasms of the hands and feet, muscle cramps, abdominal cramps, and overly active reflexes). Chronic hypocalcemia contributes to poor mineralization of bones, soft bones (osteomalacia) and osteoporosis. In children, hypocalcemia leads to rickets and impaired growth.
Hypocapnia (aka hypocarbia):   Less than the normal level of carbon dioxide in the blood.
Hypochloremia:   Low blood levels of chloride. Chloride is the major anion found in the fluid outside of cells and in blood. An anion is the negatively charged part of certain substances such as table salt (NaCl) when dissolved in liquid. Sea water has almost the same concentration of chloride ion as human fluids. The balance of chloride ion (Cl-) is closely regulated by the body. Significant decreases in chloride can have deleterious or even fatal consequences.
Hypochondria:  1. Synonym for the disorder officially called hypochondriasis. 2. The plural of hypochondrium, referring to both sides of upper abdomen just below the rib cage. A person demonstrating hypochondria is preoccupied with normal bodily functions and demonstrates fear and anxiety about the meaning of those functions. The ancients believed hypochondiasis was due to disturbed function of the organs of the upper abdomen.
Hypochondriac:  A person who has hypochondriasis, a disorder characterized by a preoccupation with body functions and the interpretation of normal body sensations (such as sweating) or minor abnormalities (such as minor aches and pains) as portending problems of major medical moment. Reassurance by physicians and others only serves to increase the hypochondriac's persistent anxiety about their health. The hypochondrium is the anatomic area of the upper abdomen just below (Greek "hypo" meaning "below") the cartilage (Greek "chondros" meaning "cartilage") of the ribs. Hypochondriasis was thought by the ancients to be due to disturbed function of the spleen and other organs in the upper abdomen.
Hypochondroplasia:  Hypochondroplasia is a type of short-limb dwarfism with shortening especially of the ends of the limbs (termed rhizomelic dwarfism). The short stature and limb shortening can be mild.
Hypocol:  One of the three major preparations of red yeast rice, a tradition Chinese medicine now used to lower cholesterol. Hypocol is also known as cholestin.
Hypodontia and nail dysgenesis:  A genetic disorder characterized by the absence of several teeth (hypodontia) and abnormalities of the nails (nail dysgenesis) at birth. The disorder is also known as Witkop syndrome or the tooth and nail syndrome (TNS).
Hypogeusia:  A reduced ability to taste things (to taste sweet, sour, bitter, or salty substances). Some people cannot detect tastes and are said to have ageusia.
Hypoglossal nerve:  The hypoglossal nerve is the twelfth cranial nerve. The twelve cranial nerves, the hypoglossal nerve included, emerge from or enter the skull (the cranium), as opposed to the spinal nerves which emerge from the vertebral column. The hypoglossal nerve supplies the muscles of the tongue.
Hypoglossal neuropathy:  Disease of the hypoglossal nerve, the twelfth cranial nerve (see above). Paralysis of the hypoglossal nerve affects the tongue. It impairs speech (the speech sounds thick) and causes the tongue to deviate toward the paralyzed side. In time, the tongue diminishes in size (atrophies).
Hypoglycemia:   Low blood sugar (glucose). When symptoms of hypoglycemia occur together with a documented blood glucose under 45 mg/dl, and the symptoms promptly resolve with the administration of glucose, the diagnosis of hypoglycemia can be made with some certainty. Hypoglycemia is only significant when it is associated with symptoms. The symptoms may include anxiety, sweating, tremor, palpitations, nausea, and pallor. Hypoglycemia also starves the brain of glucose energy, which is essential for proper brain function. Lack of glucose energy to the brain can cause symptoms ranging from headache, mild confusion, and abnormal behavior, to loss of consciousness, seizure, and coma. Severe hypoglycemia can cause death.
Hypoglycemia unawareness:  A complication of diabetes in which the patient is unaware of a deep drop in blood sugar because it fails to trigger the secretion of epinephrine which generates the characteristic symptoms of hypoglycemia (such as palpitations, sweating, anxiety) that serve to warn the patient of the dropping blood glucose. The patient can then take action and eat to help reverse the hypoglycemia. Hypoglycemia unawareness can result in prolonged exposure to hypoglycemia, resulting in a seizure, loss of consciousness, or brain damage. The development of hypoglycemia unawareness also makes intensified blood glucose control more difficult and puts the patient at risk for severe hypoglycemia-related complications.
Hypoglycemic:  Relating to hypoglycemia, an abnormally low level of the sugar glucose in the blood, usually a complication of diabetes, in which the body does not produce enough insulin to fully metabolize glucose.
Hypogonadism::  A condition in which decreased production of gonadal hormones leads to below-normal function of the gonads and to retardation of sexual growth and development. (The gonads are the ovaries and testes and the hormones they normally produce include estrogen, progesterone, and testosterone.)
Hypohidrosis:  Subnormal sweating, less sweating than usual. Hidrosis meaning sweating, so hypohidrosis is literally undersweating.
Hypokalemia:  Low blood potassium. Potassium is the major positive ion (cation) found inside of cells. The chemical notation for potassium is K+. The proper level of potassium is essential for normal cell function. An abnormal decrease (or increase) of potassium can profoundly affect the nervous system and heart, and when extreme, can be fatal. The normal blood potassium level is 3.5 - 5.0 milliEquivalents/liter (mEq/L), or in international units, 3.5 - 5.0 millimoles/liter (mmol/L).
Hypomagnesemia:  Too little magnesium. Magnesium deficiency can occur due to inadequate intake or impaired intestinal absorption of magnesium. Low magnesium is often associated with low calcium (hypocalcemia) and low potassium (hypokalemia). Deficiency of magnesium causes increased irritability of the nervous system with tetany (spasms of the hands and feet, muscular twitching and cramps, spasm of the larynx, etc.). According to the National Academy of Sciences, the Recommended Dietary Allowances of magnesium are 420 milligrams per day for men and 320 milligrams per day for women. The upper limit of magnesium as supplements is 350 milligrams daily, in addition to the magnesium from food and water.
Hypomania:  A condition similar to mania but less severe. The symptoms are similar with elevated mood, increased activity, decreased need for sleep, grandiosity, racing thoughts, and the like. However, hypomanic episodes differ in that they do not cause significant distress or impair one's work, family, or social life in an obvious way while manic episodes do. Hypomanic people tend to be unusually cheerful, have more than ample energy, and need little sleep. Hypomania is a pleasurable state. It may confer a heightened sense of creativity and power. However, hypomania can subtly impair a person's judgment. Too much confidence can conceal the consequences of decisions. Hypomania can be difficult to diagnose because it may masquerade as mere happiness. It is important to diagnose hypomania because, as an expression of bipolar disorder, it can cycle into depression and carry an increased risk of suicide.
Hypomnesia:  Abnormally poor memory of the past. As compared to hypermnesia and amnesia.
Hyponatremia:  An abnormally low concentration of sodium in the blood. Too little sodium can cause cells to malfunction, and extremely low sodium can be fatal. Hyponatremia has many causes including medications such as diuretics and antidepressants, hypothyroidism, cortisone deficiency (such as in Addison's disease), dehydration, vomiting or diarrhea, severe burns, kidney or heart failure, and cirrhosis. The symptoms of hyponatremia include bloating and puffiness in the face and fingers, nausea, vomiting, muscle weakness, headache and disorientation.
Hypoparathyroidism:  Underfunction of the parathyroid glands with deficient production of the hormone parathormone which leads to low blood calcium (hypocalcemia). The parathyroid glands are located adjacent to the thyroid gland. They may be missing due to a birth defect, impaired by autoimmune disease, or surgically removed during thyroid surgery. Treatment is with oral calcium supplements and oral vitamin D. Oral vitamin D increases the gut absorption of calcium in the diet and helps to maintain normal blood calcium levels.
Hypopharyngeal diverticulum (Zenker diverticulum):  The most common type of outpouching in the esophagus, due to increased pressure causing the mucous membrane of the esophagus to herniate through a defect in the wall of esophagus. Usually located in the posterior hypopharyngeal wall, small diverticuli may not cause symptoms but larger ones may collect food and obstruct the esophagus.
Hypophosphatemia:  A less than normal blood level of phosphate.
Hypoplasia:  Underdevelopment or incomplete development of a tissue or organ. For example, there can be hypoplasia of the enamel of the teeth. Hypoplasia is less drastic than aplasia where there is no development at all.
Hypopnea:  Literally, underbreathing. Breathing that is shallower or slower than normal. Hypopnea is distinct from apnea in which there is no breathing. Hypopnea can lead to hypercapnia (excess carbon dioxide).
Hyposmia:  A reduced ability to smell and to detect odors. Some people have anosmia and can detect no odors.
Hypospadias:  A birth defect of the penis involving the urethra (the transport tube leading from the bladder to discharge urine outside the body). The urethra normally travels in the male through the full length of the penis so that the stream of urine comes from the urethral opening at the tip of the penis. However, in hypospadias the urethra does not go all the way through the penis but, instead, opens on the underside of the shaft of the penis or below the penis. Hypospadias is relatively common, affecting approximately 1 in every 500 newborn boys.
Hypotension:  Any blood pressure that is below the normal expected for an individual in a given environment. Hypotension is the opposite of hypertension (abnormally high blood pressure). Hypotension is a relative term because the blood pressure normally varies greatly with activity, age, medications, and underlying medical conditions.
Hypothalamic hamartoma:  A benign tumor of the hypothalamus, the area of the brain that controls body temperature, hunger, and thirst. (In technical terms, the hypothalamus lies beneath a structure known as the thalamus and forms the floor of the third ventricle of the brain.) A small hypothalamic hamartoma can cause the person to feel as though they have to laugh. The tumor also causes the patient to have mild epileptic seizures. The seizures can usually be controlled with medication; the laugh cannot. Larger hypothalamic hamartomas often cause more serious symptoms, including changes in mental ability and behavioral problems.
Hypothalamus:  The area at the base of the brain that controls body temperature, hunger, and thirst.
Hypothermia:  Abnormally low body temperature. The condition needs treatment at body temperatures of 35C (95 F) or below. And hypothermia becomes life threatening below body temperatures of 32.2 C (90 F). The signs and symptoms of hypothermia depend upon the body temperature. The major initial sign of hypothermia is a decrease in mental function that leads to impaired ability to make decisions. Tiredness or lethargy, changes in speech, and disorientation are typical. The person will act as if they are "drunk." The body gradually loses protective reflexes such as shivering which is an important heat-generating defense. Other muscle functions also disappear so that the person cannot walk or stand. Eventually consciousness is lost. Recognizing hypothermia can be difficult for the symptoms at first resemble other causes of change in mental and motor functions such as diabetes, stroke, alcohol or drug use, etc. The most important thing is to think of the possibility and be prepared to treat it.
Hypothyroid:  Deficiency of thyroid hormone which is normally made by the thyroid gland which is located in the front of the neck. Underactivity of the thyroid gland at birth is termed congenital hypothyroidism and leads to cretinism: growth retardation, developmental delay and other abnormal features. Congenital hypothyroidism can be due to deficiency of iodine in the mother's diet during pregnancy. The condition is detected today by newborn thyroid screening. Infantile hypothyroidism (subnormal activity of the thyroid gland) begins after birth and is manifest by features including delays in growth and development and myxedema surfacing during infancy. Myxedema is a dry waxy type of swelling, often with swollen lips and nose. Infantile hypothyroidism is synonymous with infantile myxedema.
Hypotonia:  Decreased tone of skeletal muscles. In a word, floppiness. Hypotonia is a common finding in cerebral palsy and other neuromuscular disorders. Untreated hypotonia can lead to hip dislocation and other problems. Treatment is via physical therapy. In some cases braces may be needed to permit a full range of movement despite hypotonia
Hypotonic solution:  A solution with a lower salt concentration than in normal cells of the body and the blood.
Hypoventilation:  The state in which a reduced amount of air enters the alveoli in the lungs, resulting in decreased levels of oxygen and increased levels of carbon dioxide in the blood. Hypoventilation can be due to breathing that is too shallow (hypopnea) or too slow (bradypnea) or to diminished lung function.
Hypovolemia:  An abnormal decrease in blood volume or, strictly speaking, an abnormal decrease in the volume of blood plasma.
Hypovolemic shock (aka "shock"):  A life-threatening medical condition whereby the body suffers from insufficient blood flow throughout the body. Shock often accompanies severe injury or illness. Medical shock is a medical emergency and can lead to other conditions such as lack of oxygen in the body's tissues (hypoxia), cardiac arrest or organ damage. It requires immediate treatment as symptoms can worsen rapidly.
Hypoxemia:  Abnormally low levels of oxygen in the blood. Hypoxemia may be mild to severe and leads to shortness of breath.
Hypoxia:  A subnormal concentration of oxygen.
Hypoxic-ischemic encephalopathy:  Damage to cells in the central nervous system (the brain and spinal cord) from inadequate oxygen. Hypoxic-ischemic encephalopathy allegedly may cause death in the newborn period or result in what is later recognized as developmental delay, mental retardation, or cerebral palsy. This is an area of considerable medical and medical-legal debate.
Hysterectomy:  A surgical operation to remove the uterus and, sometimes, the cervix. Removal of the entire uterus and the cervix is referred to as a total hysterectomy. Removal of the body of the uterus without removing the cervix is referred to as a subtotal hysterectomy.
Hysterosalpingogram (HSG):  A hysterosalpingogram imaging test that is used to examine the cavity of the uterus and Fallopian tubes. In a hysterosalpingogram, dye (called contrast material) is injected through a tube inserted through the vaginal into the uterus. A series of x-ray pictures are taken as the dye moves through the uterine cavity and out through the Fallopian tubes. If the Fallopian tubes are normal, the dye will flow out through the tubes into the abdominal cavity, and is then naturally absorbed by the body. The test takes about 15-30 minutes and is performed by a radiologist or gynecologist, typically in the radiology department of the hospital.



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