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Dr. Kennedy's Vocabulary Course: -M-
(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.
Vocabulary Search:Phrase  Any Words

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(A B C D E F G H I J K L M)
Marburg virus:  The virus that causes Marburg hemorrhagic fever, a disease which affects both humans and non-human primates. The Marburg virus is a genetically unique zoonotic (that is, animal-borne) RNA virus of the filovirus family, and its recognition led to the creation of this virus family. The four species of Ebola virus are the only other known members of the filovirus family. Marburg virus was first recognized in 1967, when outbreaks of hemorrhagic fever occurred simultaneously in laboratories in Marburg and Frankfurt, Germany, and in Belgrade, Yugoslavia (now Serbia).
Marfan syndrome:  An inherited disorder of connective tissue that is characterized by abnormalities of the eyes, skeleton, and cardiovascular system. Nearsightedness (myopia) is the most common eye feature in Marfan syndrome. Displacement of the lens from the center of the visual axis occurs in more than half of patients. Patients with Marfan syndrome have an increased risk for retinal detachment, glaucoma, and early cataracts. The skeleton shows bone overgrowth and loose joints. The arms and legs are unusually long, as are the fingers and toes. Due to overgrowth of the ribs, the sternum may be pushed in (pectus excavatum) or out (pectus carinatum). Scoliosis is common. Cardiovascular manifestations in Marfan syndrome include enlargement of the aorta at the level of the aortic valve, aortic aneurysm, prolapse of the mitral and tricuspid valves, and enlargement of the pulmonary artery. The major causes of disease and death in the syndrome are related to the heart and blood vessels. Marfan syndrome is inherited in an autosomal dominant manner and is caused by mutation in the FBN1 gene that encodes fibrillin 1. About 75 percent of people with Marfan syndrome have an affected parent, and 25 percent have a new gene mutation. Pregnancy can be dangerous for women with Marfan syndrome because the aorta can widen. Prevention of complications is key and includes exercise, blood pressure control, monitoring of the eyes, heart, and lungs, and physical therapy. Given good medical management, the life expectancy in Marfan syndrome now approximates that for the general population. Although I personally doubt it, one often hears the theory that Abe Lincoln had Marfan's.
Macerate:  To soften tissues after death by soaking and by enzymatic digestion.
Macewen sign:  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.
Macro- (prefix):  Prefix from the Greek "makros" meaning large or long. Examples of terms involving macro- include macrobiotic, macrocephaly, macrocytic, macroglossia, macrophage, macroscopic, and macrosomia. The opposite of macro- is micro-.
Macroangiopathy:   A disease of the large blood vessels in which fat and blood clots build up and stick to the vessel walls, blocking the flow of blood. Types of macroangiopathy include coronary artery disease (macroangiopathy in the heart), cerebrovascular disease (macroangiopathy in the brain), and peripheral vascular disease (macroangiopathy that affects, for example, vessels in the legs).
Macrobiota:  The living organisms of a region that are large enough to be seen with the naked eye.
Macrobiotic:  Referring to the macrobiota, a region's living organisms that are large enough to be seen with the naked eye.
Macrobiotic diet:  A diet that incorporates Ayurvedic principles of food combining, is based mainly on brown rice and vegetables, and claims to lengthen life. The macrobiotic diet is strictly not recommended for pregnant women or children and calls for certainty that sufficient protein is present in the adopted form of this diet.
Macrocephaly:  An abnormally large head. The opposite of macrocephaly is microcephaly. Macrocephaly can be a normal variant or be a sign of pressure within the growing head during childhood, such as from hydrocephalus.
Macrocytic:  Literally, referring to any abnormally large cell; in practice, referring to an abnormally large red blood cell. For example, macrocytic anemia is characterized by abnormally large red blood cells. The opposite of macrocytic is microcytic.
Macrogenitosomia:  A condition in which the external sex organs are prematurely or abnormally enlarged. Macrogenitosomia is associated with hormonal disorders that may also create changes in the internal sex organs.
Macroglobulinemia:  A condition in which the blood contains high levels of large proteins and is too thick to flow through small blood vessels. The large protein is an antibody called macroglobulin or IgM. One type of macroglobulinemia is Waldenstrom's macroglobulinemia, a type of cancer.
Macroglossia:  An abnormally large tongue.
Macrognathia:  An abnormally large jaw. Macrognathia can be associated with pituitary gigantism, tumors, and other disorders. Macrognathia can often be corrected with surgery. Also known as prognathic mandible.
Macroorchidism:  Abnormally large testes. To determine if the testes are too large, a device called an orchidometer is used that permits a testis to be compared to a series of plastic ovals of differing sizes. Macroorchidism is a diagnostic feature of fragile X syndrome, the most common inherited form of mental retardation. The opposite of macroorchidism is microorchidism.
Macrophage:  Literally "big eater," a type of white blood cell that ingests foreign material. Macrophages are key players in the immune response to bacteria. They are normally found in the liver, spleen, and connective tissues.
Macrophage inhibitory cytokine (MIC-1):  A growth factor produced in the placenta. There are detectable levels of MIC-1 in the blood of the mother during pregnancy. Low levels of MIC-1 in maternal serum are predictive for an elevated risk of early pregnancy loss. Also known as placental bone morphogenetic protein and placental BMP.
Macrophagic myofasciitis:  A muscle disease named for the findings seen in tissue from muscle biopsies, namely an abnormal infiltrate surrounding muscle tissue of specialized immune cells called "macrophages," a type of immune cell important to swallowing and destroying microorganisms.
Macroscopic:  Large enough to be seen with the naked eye, as opposed to microscopic. For example, a macroscopic tumor is big enough to be seen without the aid of a microscope.
Macrosomia:  An overly large body. A child with macrosomia has significant overgrowth, which can represent a hormone imbalance such as excess growth hormone.
Macrovascular:  Pertaining to the macrovasculature, the portion of the vasculature of the body comprising the larger vessels, those with an internal diameter of more than 100 microns. The term macrovascular is somewhat less used than microvascular. There is a field of microvascular surgery. Macrovacular surgery is usually simply called vascular surgery.
Macrovascular disease:  Disease of the large blood vessels, including the coronary arteries, the aorta, and the sizable arteries in the brain and in the limbs. Macrovascular disease is in contrast to microvascular disease such as occurs in persons with diabetes who have chronic hyperglycemia (assessed by glycosylated hemoglobin level) which is related to the development of microvascular disease. However, the relation of glycosylated hemoglobin to macrovascular disease is less clear and perhaps non-existent.
Macula:  A macula is a small spot. A macula on the skin is a small flat spot while the macula in the eye is a small spot where vision is keenest in the retina (the focal point).
Macular cyst:  A hole in the macula, the tiny oval area made up of millions of nerve cells located at the center of the retina responsible for sharp, central vision. The eye contains a jelly-like substance called the vitreous. As a person ages (usually by age 55), the vitreous pulls away from the retina. If the vitreous was firmly attached to the retina a hole can result when the vitreous pulls away. The size of the hole and its location on the retina determine how much it affects vision. Generally, people notice a slight distortion or reduction in eyesight. However, if the hole goes all the way through the macula, central vision and therefore your detailed fine vision can be seriously affected.
Macular degeneration:  A disease that progressively destroys the macula, the central portion of the retina, impairing central vision. Macular degeneration rarely causes blindness because only the center of vision is affected. However, injury to the macula in the center of the retina can impair the ability to see straight ahead clearly and sometimes make it difficult to read, drive, or perform other daily activities that require fine central vision.
Macular pucker:  Scar tissue in the macula, the area of the retina responsible for sharp central vision. The scar can blur and distort vision and make straight lines appear wavy.
Macular retinopathy:  Any pathologic condition or disease of the macula, the small spot in the retina where vision is keenest. Also called maculopathy.
Macular vision:  The macula is a special area in the center of the retina, the light-sensitive layer of tissue at the back of the eye. As one reads, light is focused onto the macula. There, millions of cells change the light into nerve signals that tell the brain what we are seeing. This is called macular or central vision. Thanks to central vision, one is able to read, drive, and perform other activities that require fine, sharp, straight-ahead vision. Of all species, human's have the best vision, one of the factors which has enabled us to survive.
Macule:  A circumscribed change in the color of skin that is neither raised nor depressed. Macules are completely flat and can only be appreciated by visual inspection and not by touch. Physicians refer to flat skin spots on the skin as macules, as opposed to papules. Maculopathy: Any pathologic condition or disease of the macula, the small spot in the retina where vision is keenest. Also called macular retinopathy.
Mad Deer Disease:  AKA chronic wasting disease, a Vtransmissible spongiform encephalopathy (TSE) of North American deer and elk, a progressive neurodegenerative disorder that produces spongiform changes in the brain and chronic weight loss leading to the death of these animals. There is no known relationship between chronic wasting disease (CWD) and any other TSE of animals or people.
Madelung disease:  A disorder characterized by painless symmetrical diffuse deposits of fat beneath the skin of the neck, upper trunk, arms and legs.
Maggot:  A soft-bodied wormlike larva of a fly that lays its eggs in living or especially in decaying tissues. Certain blowfly maggots -- notably, those of the blackbottle fly (Phormia regina) and the greenbottle fly (Phaenicia sericata) -- were (and sometimes still are) used in medicine to consume and clear away both bacteria and dead tissue from deep wounds and so promote their healing. This was a favorite part of the treatment of osteomyelitis (infection of bone) and other deep suppurative (pus-filled) lesions. In a sense it was biologic (rather than surgical) debridement of a wound. The maggots also promoted healing by secreting allantoin, a supposedly salutary substance found also in fetal urine.
Magic bullet:  Or, sometimes, silver bullet. 1. The perfect drug to cure a disease with no danger of side effects.
Magnesia:  A town in present day Turkey where an ore containing magnesium carbonate was mined. Milk of Magnesia, the laxative, is magnesium hydroxide.
Magnesium:  A mineral (atomic number 12) involved in many processes in the body including nerve signaling, the building of healthy bones, and normal muscle contraction. About 350 enzymes are known to depend on magnesium.
Magnesium deficiency:  Can occur due to inadequate intake or impaired intestinal absorption of magnesium. Low magnesium (hypomagnesemia) 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.).
Magnesium excess:  Persons with impaired kidney function should be especially careful about their magnesium intake because they can accumulate magnesium, a dangerous situation.
Magnesium sulfate:  A remarkably versatile compound administered intramuscularly and intravenously as an anticonvulsant and as a tocolytic agent (to halt premature labor), taken by mouth as a fast-acting laxative, and applied locally as an anti-inflammatory. Informally called mag sulfate. Also known as Epsom salt.
Magnet therapy:  An alternative therapy in which magnetic fields are administered by application of magnets to certain parts of the body, by magnetic field-generating machines, or by magnetic mattresses or blankets. Magnet therapy has been promoted to diagnose and/or treat arthritis, cancer, circulatory disorders, diabetic neuropathy (nerve disease), fibromyalgia, HIV/AIDS, immune dysfunction, infection, inflammation, insomnia, multiple sclerosis, muscle pain, neuropathy, pain, rheumatoid arthritis, sciatica, stress and to increase energy and prolong life, There is no convincing evidence that magnet therapy is useful in any of these regards. Body magnets are contraindicated in people having radiology, an MRI or wearing a cardiac pacemaker. Also known as biomagnetic therapy or electromagnetic field therapy.
Magnetic resonance elastography:  An imaging technique used to measure the elasticity of tissue by gently shaking the tissue in a magnetic resonance imaging (MRI) machine. The technique employs standard MRI equipment with a few modifications and a vibrating metal plate placed on the skin. Magnetic resonance elastography (MRE) works by measuring the wavelength of the vibrations sent through the tissues. Pulsing the magnetic field in the MRI scanner in tune with the mechanical vibrations freezes the pattern of waves, permitting the wavelength to be measured. The elasticity of the tissue can then be calculated using this measure. MRE is being applied to the study of skeletal muscle since the stiffness of a muscle changes during muscle contraction. The technique may also be applied to breast cancer and other tumors that tend to be harder than the surrounding normal tissue.
Magnetic resonance imaging:  A procedure that uses magnetism, radio waves, and a computer to create pictures of areas inside the body. Abbreviated MRI.
Magnetic resonance perfusion imaging:  A special type of magnetic resonance imaging (MRI) that uses an injected dye in order to see blood flow through tissues.
Magnetic resonance spectroscopic imaging:  (MRSI) A noninvasive imaging method that provides information about cellular activity (metabolic information). It is used in oncology along with magnetic resonance imaging (MRI) which provides information about the shape and size of the tumor (spacial information). Also called 1H-nuclear magnetic resonance spectroscopic imaging and proton magnetic resonance spectroscopic imaging.
Magnetic-targeted carrier:  A tiny bead made from particles of iron and carbon that can be attached to a drug. A magnet applied from outside the body then can direct the drug, for example, to the site of a tumor. This can keep a larger dose of the drug at the tumor site for a longer period of time, and help protect healthy tissue from the side effects of chemotherapy.
Major:  In general, something that is more than something else. For example, the teres major muscle is larger than the teres minor muscle.
Major anomaly:  An unusual anatomic feature that is of serious medical or cosmetic consequence to the patient. For example, a major anomaly might be a cleft lip and palate. By contrast, a minor anomaly is an unusual anatomic feature not of serious medical or cosmetic consequence to the patient. For example, a minor anomaly might be curvature of the second toe so it overlaps the third toe.
Major anxiety disorder:  A major disorder characterized by excessive, irrational fear and dread. The major anxiety disorders are: panic disorder, obsessive-compulsive disorder, PTSD (post-traumatic stress disorder), social phobia, specific phobias such as claustrophobia and generalized anxiety disorder.
Major depression:  The characteristic signs and symptoms of major depression include loss of interest in activities that were once interesting or enjoyable, including sex; loss of appetite (anorexia) with weight loss or overeating with weight gain; loss of emotional expression (flat affect); a persistently sad, anxious or empty mood; feelings of hopelessness, pessimism, guilt, worthlessness, or helplessness; social withdrawal; unusual fatigue, low energy level, a feeling of being slowed down; sleep disturbance with insomnia, early-morning awakening, or oversleeping; trouble concentrating, remembering, or making decisions; unusual restlessness or irritability; persistent physical problems such as headaches, digestive disorders, or chronic pain that do not respond to treatment; thoughts of death or suicide or suicide attempts. Alcohol or drug abuse may also be signs of depression. Disabling episodes of major depression can occur once or a number of times in a lifetime.
Major gene:  A gene that is necessary and sufficient by itself to cause a condition. For example, the APC gene is a major gene for colorectal cancer.
Major histocompatibility complex:  Abbreviated MHC. A cluster of genes located on chromosome 6 concerned with antigen production and critical to the success of transplantation. The MHC includes the human leukocyte antigen (HLA) genes.
Malabsorption:  Poor intestinal absorption of nutrients. Malabsorption can occur from diseases that injure the bowels, such as Crohn's disease, Whipple's disease, celiac disease, and many others.
Malacia:  A general term signifying softening. For example, osteomalacia is softening of bone, usually due to deficiency of calcium and vitamin D.
Malady:  From the French maladie meaning illness.
Malaise:  A vague feeling of discomfort, the cause of which may not be obvious but is often sensed as 'just not right.' From the Old French mal- "bad or ill" and aise "ease".
Malar:  Referring to the cheek. For example, a malar rash is a rash that appears over the cheeks.
Malaria:  An infectious disease caused by protozoan parasites from the Plasmodium family that can be transmitted by the sting of the Anopheles mosquito or by a contaminated needle or transfusion. Falciparum malaria (Plasmodium falciparum) is the most deadly type. Prior to the age of effective anti-malarial drugs the best defense against malaria was to avoid mosquitos - which meant avoiding swamps. Since the area now occupied by Washington DC was originally a swamp, lawmakers in the early days would leave for their native states six months out of the year to avoid mosquitos and thus avoid malaria. Therefore less laws were passed and there was less government interference in the private sector, thus the rapid growth of our country. Perhaps we should bring back the swamp with the mosquitos and ban antimalaria drugs in DC.
Malaria, falciparum:  The most dangerous type of malaria, which is caused by the parasite Plasmodium falciparum. Falciparum malaria is associated with high levels of parasites in the blood and has the highest death rate and rate of complications of all types of malaria. Red blood cells that are infected with the parasite tend to sludge and lead to microinfarctions (tiny areas of dead tissue due to lack of oxygen) in capillaries in the brain, liver, adrenal gland, intestinal tract, kidneys, lungs, and other organs. Patients should be treated in a hospital setting, using intravenous medications.
Malariologist:  Someone who is versed in or engaged in the study of malaria.
Malariology:  The study of malaria.
Malattia leventinese:  An hereditary form of macular degeneration that results in progressive and irreversible visual loss. This disease is characterized by the appearance in early adulthood of small round white spots (drusen), particularly in the macula of the retina, which progress to form a honeycomb pattern. Malattia leventinese is inherited in an autosomal dominant manner. The condition was clinically first recognized and reported in 1899 by Robert Walter Doyne (1857-1916), an ophthalmologist in Oxford, England. It is also known as Doyne honeycomb retinal dystrophy (DHRD) and as autosomal dominant radial drusen.
Male breast cancer:  Breast cancer in men. Male breast cancer is much less common than breast cancer in women. Fewer than 1 percent of persons with breast cancer are male. However, breast cancer is no less dangerous in males than in females. After the diagnosis of breast cancer is made, the mortality rates are virtually the same for men and for women.
Male chromosome complement:  The whole set of chromosomes for a human male. The large majority of males have a 46,XY chromosome complement: 46 chromosomes, including 1 X and 1 Y chromosome. A minority of males have other chromosome constitutions, such as 47,XXY (47 chromosomes, including 2 X chromosomes and 1 Y chromosome) or 47,XYY (47 chromosomes, including 1 X and 2 Y chromosomes).
Male menopause:  The decline in testosterone levels observed in men as they age causes a clinically significant and potentially treatable set of symptoms, including sexual dysfunction, mood changes, weight gain, fatigue, and other nonspecific symptoms.
Male pelvis:  The lower part of the abdomen that is located between the hip bones in a male. The male pelvis is more robust, narrower, and taller than the female pelvis. The angle of the male pubic arch and the sacrum are narrower as well.
Malformation:  A structural defect in the body due to abnormal embryonic or fetal development. There are many types of malformations. For example, cleft lip and cleft palate.
Malignancy:  A tumor that is malignant (cancerous), that can invade and destroy nearby tissue, and that may spread (metastasize) to other parts of the body.
Malignant:  1. Tending to be severe and become progressively worse, as in malignant hypertension. 2. In regard to a tumor, having the properties of a malignancy that can invade and destroy nearby tissue and that may spread (metastasize) to other parts of the body. The word malignant comes the Latin combination of "mal" meaning "bad" and "nascor" meaning "to be born"; malignant literally means "born to be bad."
Malignant ascites:  A condition in which fluid containing cancer cells collects within the abdomen.
Malignant giant cell tumor:  A type of bone tumor that is characterized by massive destruction of bone near the end (epiphysis) of a long bone and causes pain and restricts movement. The most common site of malignant giant cell tumor is the knee. Diagnosis is made by examining a sample of the affected area. Treatment involves excising the affected area, usually followed by chemotherapy or radiation.
Malignant hyperthermia:  A series of potentially fatal problems that can occur during surgery, 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.
Malleolus:  The rounded bony prominence on either side of the ankle joint.
Malleus:  A tiny bone in the middle ear that is shaped like a minute mallet.
Malnutrition:  A term used to refer to any condition in which the body does not receive enough nutrients for proper function. Malnutrition may range from mild to severe and life-threatening. It can be a result of starvation, in which a person has an inadequate intake of calories, or it may be related to a deficiency of one particular nutrient (for example, vitamin C deficiency). Malnutrition can also occur because a person can not properly digest or absorb nutrients from the food they consume, as may occur with certain medical conditions. Malnutrition remains a significant global problem, especially in developing countries.
Malrotated ear:  An ear that is slanted more than usual. Technically, an ear is slanted when the angle of the slope of the auricle is more than 15 degrees from the perpendicular. Slanted ears are considered a minor anomaly. The presence of 2 or more minor anomalies in a child increases the probability that the child has a major malformation.
Malrotation of the intestine:  Failure of the intestine to rotate normally during the development of the embryo. One of the dangers of malrotation of the intestine is that the intestine may be obstructed by abnormal bands or twist on its own blood supply, a condition called volvulus.
MALT:  Mucosa-associated lymphoid tissue.
MALT lymphoma:  A low grade type of malignancy that arises in cells in mucosal tissue which are involved in antibody production. These lymphomas occur most often in the stomach but can also arise in the lung, thyroid, salivary glands, eye, skin, or soft tissues. MALT stands for mucosa-associated lymphoid tissue. MALT lymphomas are typically slow growing and are usually diagnosed at an early stage. They may be treated with low doses of radiotherapy or removed by surgery. If they have spread, they are treated with chemotherapy. The outlook is good, even when the disease is quite widespread.
MAM:  Menstrually associated migraine.
Mammary gland:  One of the two half-moon-shaped glands on either side of the adult female chest, which with fatty tissue and the nipple make up the breast. Within each mammary gland is a network of sacs that produce milk during lactation and send it to the nipple via a system of ducts.
Mammogram:  An X-ray of the breast that is taken with a device that compresses and flattens the breast. A mammogram can help a health professional decide whether a lump in the breast is a gland, a harmless cyst, or a tumor. A mammogram can cause pressure, discomfort, and some soreness that lasts for a little while after the procedure. If the mammogram result raises suspicions about cancer, a biopsy is usually the next step.
Managed care:  Any system that manages health care delivery to control costs. Typically, managed care systems rely on a primary care physician who acts as a gatekeeper for other services, such as specialized medical care, surgery, and physical therapy.
Mandible:  The bone of the lower jaw. The joint where the mandible meets the upper jaw at the temporal bone is called the temporomandibular joint.
Mania:  An abnormally elevated mood state characterized by such symptoms as inappropriate elation, increased irritability, severe insomnia, grandiose notions, increased speed and/or volume of speech, disconnected and racing thoughts, increased sexual desire, markedly increased energy and activity level, poor judgment, and inappropriate social behavior. A mild form in mania that does not require hospitalization is termed hypomania. Mania that also features symptoms of depression ("agitated depression") is called mixed mania. Mania is the Greek word for madness. It is derived from mainmai, to rave in anger. The Maniai in Greek mythology were the Furies who pursued those who had done unavenged crimes and drove them to madness.
Manic-depression:  Alternating moods of abnormal highs (mania) and lows (depression). Called bipolar disorder because of the swings between these opposing poles in mood. A type of depressive disease. Not nearly as prevalent as other forms of depressive disorders. Sometimes the mood switches are dramatic and rapid, but most often they are gradual. Mania often affects thinking, judgment, and social behavior in ways that cause serious problems and embarrassment. For example, unwise business or financial decisions may be made when an individual is in a manic phase. Bipolar disorder is often a chronic recurring condition. A mild to moderate level of mania is called hypomania. Hypomania may feel good to the person who experiences it and may even be associated with good functioning and enhanced productivity. Thus even when family and friends learn to recognize the mood swings as possible bipolar disorder, the person may deny that anything is wrong. Without proper treatment, however, hypomania can become severe mania in some people or can switch into depression.
Manometry:  The measurement of pressure using a device called a manometer. Esophageal manometry is done to measure muscle pressure and movements in the esophagus in the evaluation of achalasia. Anal manometry, the measurement of the pressure generated by the anal sphincter, is used to evaluate anal incompetence and fecal incontinence. A blood pressure cuff is a familiar form of sphygmomanometer.
Manorexia:  A term that has been used to refer to anorexia nervosa in males. This is not an officially recognized medical term but has been frequently used in media reports. See also anorexia nervosa.
Mantoux test:  A skin test for tuberculosis, named for the French physician Charles Mantoux (1877-1947). AKA the tuberculin skin test
MAO inhibitor:  One of a family of medications (brand names: Aurorex, Nardil, Parnate) that act to limit the activity of monoamine oxydase (MAO) in the nervous system. MAOIs are prescribed to treat depression, anxiety, migraine, and selected other conditions in patients who are not responsive to other medications. They interact with many over-the-counter medications and some foods, so patients taking MAOIs must be educated about what to avoid and must follow a restricted diet.
MAP:  The commonly used term for Mycobacterium avium subspecies paratuberculosis.
Map, contig:  A map depicting the relative order of a linked library of small overlapping clones representing a complete chromosome segment. A contig is a chromosome map showing the locations of those regions of a chromosome where contiguous DNA segments overlap.
Map, cytogenetic:   A genetic term referring to the visual appearance of a chromosome when stained and examined under a microscope. Particularly important are visually distinct regions, called light and dark bands, which give each of the chromosomes a unique appearance. This feature allows a person's chromosomes to be studied in a clinical test known as a karyotype, which allows scientists to look for chromosomal alterations.
Map, linkage:  A map of the genes on a chromosome based on linkage analysis. A linkage map does not show the physical distances between genes but rather their relative positions, as determined by how often two gene loci are inherited together. The closer two genes are (the more tightly they are linked), the more often they will be inherited together. Linkage distance is measured in centimorgans (cM).
Map, physical:  A map of the locations of identifiable landmarks on chromosomes. Physical distance is measured in base pairs.
Map-dot-fingerprint type corneal dystrophy:  A disorder in which the cornea (the normally clear front window of the eye) shows geographic map-like lines, dots (or microcysts), and grayish fingerprint lines on examination with a slit-lamp, a device that focuses a high intensity light beam as a slit while the examiner looks at the front of the eye through a magnifying scope.The disorder is usually silent and without symptoms. However, about one patient in ten has recurrent erosion of the cornea that usually begins after the age 30.Conversely, half of patients with recurrent corneal erosions of idiopathic (unknown) origin have this disorder. Under the microscope, a structure called the epithelial basement membrane is abnormal. The disorder is therefore sometimes called epithelial basement corneal dystrophy. The disorder was first described by Cogan and colleagues in 1964. Hence, the name: Cogan corneal dystrophy. It is also known (to add to the confusion) as microcystic corneal dystrophy.
Maple syrup urine disease:  A hereditary disease that is due to deficiency of an enzyme involved in amino acid metabolism, characterized by urine that smells like maple syrup. In maple syrup urine disease, the three branched-chain amino acids (leucine, isoleucine, and valine) cannot be metabolized (processed), and they build up in the blood, causing problems with brain function and leading to mental retardation, physical disability, and death, if not treated. Treatment involves use of a special diet and monitoring of protein intake.
Mapping:  Charting the location of genes on chromosomes.
Marasmus:  Wasting away, as occurs with children who have kwashiorkor. Also called cachexia, is usually a result of protein and calorie deficiency.
Marburg virus:  The virus that causes Marburg hemorrhagic fever, a disease which affects both humans and non-human primates. The Marburg virus is a genetically unique zoonotic (that is, animal-borne) RNA virus of the filovirus family, and its recognition led to the creation of this virus family. The four species of Ebola virus are the only other known members of the filovirus family. Marburg virus was first recognized in 1967, when outbreaks of hemorrhagic fever occurred simultaneously in laboratories in Marburg and Frankfurt, Germany, and in Belgrade, Yugoslavia (now Serbia).
Marfan syndrome:  An inherited disorder of connective tissue that is characterized by abnormalities of the eyes, skeleton, and cardiovascular system. Nearsightedness is the most common eye feature in Marfan syndrome. Displacement of the lens from the center of the pupil occurs in more than half of patients. Patients with Marfan syndrome have an increased risk for retinal detachment, glaucoma, and early cataracts. The skeleton shows bone overgrowth and loose joints. The arms and legs are unusually long, as are the fingers and toes. Due to overgrowth of the ribs, the sternum may be pushed in (pectus excavatum) or out (pectus carinatum). Scoliosis is common. Cardiovascular manifestations in Marfan syndrome include enlargement of the aorta at the level of the aortic valve, aortic aneurysm, prolapse of the mitral and tricuspid valves, and enlargement of the pulmonary artery. The major causes of disease and death in the syndrome are related to the heart and blood vessels. Marfan syndrome is inherited in an autosomal dominant manner. Death odccurs on average around age 40. Some speculate that Abraham Lincoln had Marfan's but this is unlikely as he lived to age 56 and apparently had none of the concommitant conditions.
Marie-Strümpell disease:  A synonym for ankylosing spondylitis. Named for the French neurologist Pierre Marie (1853-1940) and the German neurologist whose full name was Ernst Adolf Gustav Gottfried von Strumpell (1853-1925). See: Ankylosing Spondylitis.
Marinesco-Sjogren syndrome:  A genetic disorder characterized by very small stature, cerebellar ataxia (wobbliness), cataracts, muscle weakness, hypogonadism (low gonadal function), and developmental and mental retardation.
Marker (aka Marker Gene):  A piece of DNA that lies on a chromosome so close to a gene that the marker and the gene are inherited together. A marker is thus an identifiable heritable spot on a chromosome. A marker can be an expressed region of DNA (a gene) or a segment of DNA with no known coding function. All that matters is that the marker can be detected and trailed.
Marker chromosome:   An abnormal chromosome that is distinctive in appearance but not fully identified. A marker chromosome is not necessarily a marker for a specific disease or abnormality, but it can be distinguished under the microscope from all the normal human chromosomes. For example, the fragile X (FRAXA) chromosome was once called the marker X.
Marmoreal:  Resembling marble. For example, the bone in osteoporosis appears marmoreal. From the Latin noun "marmor" meaning "marble."
Maroteaux-Lamy syndrome:  A form of mucopolysaccharidosis with the clinical onset before age 3 that is characterized by an inability to metabolize dermatan sulfate. This leads to abnormal accumulation of dermatan sulfate, resulting in mild to severe changes in muscle, bone, skin, and other tissues, particularly the heart. Diagnosis is by examining leukocytes and cultured skin fibroblasts, or 24-hour urine collection to search for high levels of dermatan sulfate. There is no current treatment for the syndrome, but individual symptoms and problems may respond to physical therapy, medication, or surgery. Due to heart damage, death usually occurs before age 40. Also known as mucopolysaccharidosis type VI.
Marriage, cousin:  A form of consanguinity. Everyone carries recessive alleles, genes that are generally harmless in the heterozygous state but that in the company of another identical gene are capable of causing disease. We are all genetic reservoirs for genetic disease. Since first cousins share a set of grandparents, for any particular allele (gene) in the father, the chance that the mother inherited the same allele from the same source is 1/8 (one out of four in the first generation and one out of four in the second generation. There are always added risks from the mating of closely related persons.
Marrow:  The bone marrow.
Marsh fever:  See malaria.
Marshall-Smith syndrome:  A disorder characterized by advanced bone age at birth, broad forehead, prominent eyes, and small chin. There is difficulty feeding, failure to thrive, retarded psychomotor development, and predisposition to respiratory infection. It may be fatal within the first years of life. The cause of the syndrome is unknown.
Martorell syndrome:   Named after Fernando Martorell Otzet, Spanish cardiologist (1906-1984). In 1944 Martorell provided an excellent description of a syndrome also known today as Takayasu disease. See: Takayasu disease.
MASA syndrome:  MASA stands for mental retardation, aphasia, shuffling gait, and adducted thumbs. Features of the syndrome include: 1.neurologically: mental retardation and aphasia (lack of speech); 2.limbs: adducted (clasped) thumbs, absent extensor pollicis longus and/or brevis muscles to the thumb, shuffling gait, and leg spasticity; 3.growth: small body size; 4.skeleton: lumbar lordosis (sway back). MASA is inherited as an X-linked trait and so affects mainly boys. Alternative names for MASA include clasped thumb and mental retardation, congenital clasped thumb with mental retardation, adducted thumb with mental retardation, and the Gareis- Mason syndrome.
Mask of pregnancy:  Muddy-brown pigmentation on the cheeks or elsewhere on the face that develops in about half of all women during pregnancy. Some women also develop it outside pregnancy, as do some women on hormone therapy. The pigmentation is worsened by ultraviolet (UV) light, which tends to darken it. Regular use of a broad-spectrum sunscreen against both UVA and UVB can prevent progression of the condition. The hyperpigmentation (excess pigment in the skin) usually lightens up with the use of topical treatment with bleaching agents, together with the topical application of retinoin (vitamin A acid, Retin-A). Light chemical peels can also aid and abet the effects of the topical therapy. Also known as melasma or chloasma.
Masklike face:  An expressionless face with little or no sense of animation; a face that is more like a mask than a normal face. Masklike face is seen in a number of disorders, including Parkinson's disease and myotonic dystrophy.
Masochism:  The derivation of pleasure from one's own pain. Masochism is considered a sexual disorder (paraphilia). Named after the 19th-century Austrian writer Leopold von Sacher-Masoch.
Mass spectrometry:  A process used to identify chemicals in a substance by their mass and charge. Mass spectrometers are instruments that measure mass and charge of molecules. A mass spectrometer also can determine how much of a compound is present in a mixture. Also known as mass spectroscopy. See also: Tandem mass spectrometry.
MASS syndrome:  A heritable disorder of connective tissue characterized by involvement of the mitral valve, aorta, skeleton, and skin. Hence, the acronym MASS (Mitral valve, Aorta, Skeleton, Skin). The MASS syndrome is due to a mutation in FBN1, the fibrillin 1 gene. The same gene as is mutated in Marfan syndrome.
Masseter:  The muscle that raises the lower jaw.
Mast cell:  A granulocyte (aka mastocyte)found in connective tissue whose normal function is unknown but that is frequently injured during allergic reactions. When a mast cell is injured, it releases strong chemicals, including histamine, into the tissues and blood. These chemicals are very irritating and cause itching, swelling, and fluid leaking from cells. They can also cause muscle spasm, leading to lung and throat tightening (as is found in asthma) and loss of voice.
Mast cell tumor:  A mastocytoma (see below).
Mast syndrome:  An autosomal recessive form of hereditary spastic paraplegia with dementia first described in the Old Order Amish. The disease usually surfaces in early adulthood and is slowly progressive. The Mast syndrome gene is in chromosome 15q22.31 Its protein product is called maspardin.
Mastalgia:  Pain in the breast or mammary gland, whether serious or not. Mastalgia has many causes including injury, infection, and plugged milk ducts.
Mastectomy:  A general term for removal of the breast, usually to remove cancerous tissue. The operation can be done in a hospital or in an outpatient clinic, depending on how extensive the surgery needs to be. After a mastectomy, reconstructive surgery may be performed to restore a more normal appearance. In cases of nonmetastatic breast cancer, a lumpectomy 'with radiation, chemotherapy, or a combination of these treatments' is sometimes performed as an alternative to mastectomy.
Masticate:  To chew.
Mastitis:  Inflammation of one or more mammary glands within the breast, usually in a lactating woman. Mastitis can be felt as a hard, sore spot within the breast. Mastitis can be caused by an infection in the breast or by a plugged milk duct. Treatment includes resting and applying warm compresses to the affected area, and for those who are lactating, nursing or expressing milk frequently.
Mastocyte:  A mast cell.
Mastocytoma:  A form of mastocytosis characterized by a benign nodular skin tumor infiltrated by mast cells. Usually present at birth or in early childhood and resolves spontaneously. Also called a mast cell tumor.
Mastoid:  The rounded protrusion of bone just behind the ear. The mastoid was once thought to look like a breast (hence its name).
Mastoiditis:  Inflammation of the mastoid, which often occurs secondarily to ear infection.
Materfamilias:  The female head of the family; the mother figure. Materfamilias is the Latin for mother of the household. It is compounded from mater (mother) + familias, which comes from familia (household), from famulus (servant, slave) (??). The masculine counterpart is the paterfamilias.
Materia medica:  1. The branch of medical science concerned with the study of drugs used in the treatment of disease: includes pharmacology, clinical pharmacology, and the history and physical and chemical properties of drugs. 2. The drugs used in the treatment of disease. A synonym for pharmacology.
Maternal:  Pertaining to the mother.
Maternal age:  The age of the mother at the time of delivery. Advanced maternal age is usually defined as age 35 or more at delivery. Advanced maternal age predisposes to Down syndrome (trisomy 21). The risk of having a Down syndrome baby rises with maternal age. It essentially doubles from 1 in 725 at maternal age 32 to 1 in 365 at maternal age 35. And the risk continues to climb with the years and is 1 in 32 at maternal age 45.
Maternal mortality rate:  The number of registered maternal deaths due to birth- or pregnancy-related complications per 100,000 registered live births.
Maternal myasthenia gravis:  The presence of myasthenia gravis in a pregnant woman. During pregnancy in a woman with myasthenia, the anti-AChR antibodies can cross the placenta and block the function of the fetal form of AChR leading to fetal paralysis. Fetal and neonatal death is a common consequence. Babies who survive often have arthrogryposis multiplex congenita
Maternal phenylketonuria:  A mother with the genetic disease phenylketonuria (PKU) whose high blood levels of phenylalanine (phe) are dangerous to a developing fetus. High PKU is a teratogen (a provoker of birth defects). It can damage a baby before birth. Women with PKU who are off the special PKU diet should restart back it, ideally prior to conception. During pregnancy they must be on the diet and have their blood phe levels carefully monitored. If the maternal PKU is not controlled, the baby (who does not have PKU) is at risk for congenital heart disease, growth retardation, microcephaly (abnormally small head), and mental retardation.
Maternal serum alpha-fetoprotein (MSAFP):  A plasma protein normally produced by the fetus, in the mother's blood. MSAFP serves as the basis for some valuable tests. Alpha-fetoprotein is manufactured principally in the fetus's liver and gastrointestinal (GI) tract and the yolk sac, a structure temporarily present during embryonic development. The alpha-fetoprotein level is typically high in the fetus's blood. It decreases in the baby's blood after birth. And by one year of age, it is virtually undetectable. During pregnancy, alpha-fetoprotein normally crosses the placenta from the fetal circulation and appears in the mother's blood. The alpha-fetoprotein level in the mother's blood (the maternal serum alpha-fetoprotein) provides a screening test for several disorders including open neural tube defects (anencephaly and spina bifida) and Down syndrome (and other chromosome abnormalities). The maternal serum alpha-fetoprotein tends to be high with open neural tube defects such as anencephaly and spina bifida (meningomyelocele) and Low with Down syndrome (trisomy 21, an extra chromosome number 21). Alpha-fetoprotein production is essentially zero after a year of age. However, it increases again under the stimulus of some liver diseases. It may, for example, be produced by viral hepatitis and cirrhosis of the liver. Alpha-fetoprotein is also made by primary liver tumors (hepatomas) and by germ cell tumors (teratocarcinoma and embryonal cell carcinomas). A person's serum alpha-fetoprotein level can therefore be used to help detect these conditions and monitor cirrhosis of the liver.
Materteral:  1. Relating to a maternal aunt. 2. Figuratively, suggestive of an aunt on either side of the family. 3. In medical genetics, pertaining to an aunt. An materteral relationship is the genetic relationship between aunts and their nieces and nephews. Materteral is synonymous with materterine. From the Latin matertera meaning maternal aunt, from mater meaning mother. The masculine counterpart of avuncular (like an uncle).
Mathematics disorder:  A condition characterized by math skills that are significantly below normal, given the person's age, intelligence, and education. It can be seen as the counterpart to dyslexia or as a special form of dyslexia. A mathematics disorder can include problems writing or printing numbers, counting, adding and subtracting, interpreting simple mathematical signs such as +, -, and x, and learning terms that include numbers. Mathematics disorder often comes to attention in elementary school when math comes to the fore as a key part of the curriculum. About 1% of children in the U.S. have a mathematics disorder. The diagnosis is confirmed by special tests. Treatment includes tutoring, special math classrooms with expert math teachers, and other educational aids that focus on math skills.
Matricectomy:   the process of surgically or chemically destroying all or part of the base nail portion called the nail matrix. Complete destruction of the nail matrix results in permanent loss of that portion of the nail. Once the nail matrix is fully removed or destroyed, a new nail plate cannot ever be regenerated. This surgical procedure is commonly curative for recurrent cases of ingrown toenails.
Maturity onset diabetes of the young (MODY):  Diabetes mellitus that has early onset (usually before the age of 25), is non-insulin-dependent, and is inherited in an autosomal dominant manner. MODY is often considered a subtype of type 2 diabetes but it is unlike the usual type 2 diabetes in that insulin secretion, not the action of insulin, is impaired. There is no problem with insulin sensitivity. MODY accounts for 2-5% of all non-insulin-dependent diabetes.
Maxilla:  The major bone of the upper jaw.
MCAD deficiency:  Deficiency of an enzyme that makes it impossible to digest certain kinds of fat. MCAD stands for medium-chain acyl-CoA dehydrogenase. Children born with MCAD deficiency cannot metabolize (digest) medium-chain fats such as coconut oil. If undiagnosed, the disorder can lead to metabolic collapse, coma and death. Babies who survive run the risk of severe brain damage. Treatment involves strict attention to what the baby eats. The child must avoid medium-chain fats in the diet. It is a life-long disorder. MCAD deficiency affects about 1 of every 15,000 babies born in the US.
McArdle disease:  Glycogen storage disease type V and the most common type of glycogen storage disease. McArdle disease is an autosomal recessive disorder caused by mutations in the gene that encodes myophosphorylase, an enzyme that is essential for glycogenolysis. Exercise intolerance usually develops during childhood, along with pain, cramps, and fatigue in exercised muscle.
MCAT:  The Medical College Admissions Test, a test that is required of all applicants to medical school in the U.S. and Canada. The MCAT is "a standardized test used to assess applicants' science knowledge, reasoning, and communication and writing skills." The MCAT is administered by the Association of American Medical Colleges. All we docs had to pass the MCAT to gain admission to medical school. Study hard, no problem. Party hard, big problem. This could be why we docs are so boring.
McBurney's point:  McBurney's point is the most tender area of the abdomen of patients in the early stage of appendicitis. McBurney's point is named after the 19th-century New York surgeon Charles McBurney (1845-1913) who was the leading authority in his day on the diagnosis and treatment of appendicitis. Dr. McBurney in 1889 showed that incipient appendicitis could be detected by applying pressure to a particular point in the right lower abdomen, an area he called the "seat of greatest pain." Five years later, Dr. McBurney described the surgical incision he made in the right lower part of the abdomen to remove the inflamed appendix. This is now referred to as "McBurney's incision."
McCune-Albright syndrome:  A genetic disorder of bones, skin pigmentation and hormonal problems with premature sexual development. Also called Albright syndrome or polyostotic fibrous dysplasia.
McKusick-Kaufman syndrome:  A genetic disorder in which there is build-up of fluids (called hydrometrocolpos) in the vagina and the uterus as a result of a membrane across the vagina which holds back the cervical fluid secreted in response to the mother's hormones during pregnancy. Boys with this disease have the opening for urine on the underside of the penis (hypospadias). Other features (in both girls and boys) include extra fingers and toes (polydactyly) and heart defects at birth.
MCL (medial collateral ligament) of the knee:  The knee joint is surrounded by a joint capsule with ligaments strapping the inside and outside of the joint (collateral ligaments) as well as crossing within the joint (cruciate ligaments). These ligaments provide stability and strength to the knee joint. The medial collateral ligament of the knee is the cruciate ligament on the inner aspect of the inside of the joint.
Meadow syndrome:  After Dr. Roy Meadow, the pediatrician who coined the term Munchhausen syndrome by proxy: the manufacturing of symptoms in another person, typically a child, to gain the attention of medical personnel.
Mean cell hemoglobin (MCH):  The average amount of hemoglobin in the average red cell. It is a standard part of the complete blood count. To much or too little hemoglobin can help make the diagnosis of specific disease states.
Mean cell volume (MCV):  A standard part of the complete blood count, the average volume of a red blood cell. Unusually small or unusually large red blood cells can point to specific disease states.
Measles:  An acute and highly contagious viral disease characterized by fever, runny nose, cough, red eyes, and a spreading skin rash. Also known as rubeola, is a potentially disastrous disease which can be complicated by ear infections, pneumonia, encephalitis (which can cause convulsions, mental retardation, and even death), the sudden onset of low blood platelet levels with severe bleeding (acute thrombocytopenic purpura), or a chronic brain disease that occurs months to years after an attack of measles (subacute sclerosing panencephalitis). During pregnancy, exposure to the measles virus may trigger miscarriage or premature delivery.
Measles encephalitis:  Inflammation of the brain during recovery from measles infection. Measles encephalitis occurs in approximately 1 in 1,000 to 2,000 cases of measles, starting up to 3 weeks after onset of the rash and causing high fever, convulsions, and coma. It carries a 10-20 percent mortality rate and may lead to permanent central nervous system impairment.
Measles syndrome, atypical (AMS):  An altered expression of measles, AMS begins suddenly with high fever, headache, cough, and abdominal pain. The rash may appear 1 to 2 days later, often beginning on the limbs. Swelling (edema) of the hands and feet may occur. Pneumonia is common and may persist for 3 months or more. AMS occurs in persons who were incompletely immunized against measles.
Meatus:  An opening or a passageway. For example, the meatus of the ear is the opening to the ear canal.
Mechanical ventilation:  Use of a machine called a ventilator or respirator to improve the exchange of air between the lungs and the atmosphere.
Meckel's diverticulum:  An outpouching from the small intestine, due to failure of obliteration of the yolk stalk (which normally disappears during embryonic life). About 2% of people have a Meckel's diverticulum. It is usually located about 2 feet (60 cm) above the junction of the small intestine with the colon (the large intestine). A Meckel's diverticulum can become inflamed, ulcerate, bleed, perforate or cause obstruction of the small bowel. If it is inflamed or perforated it is usually removed by surgery.
Meconium:  Dark, sticky material that is normally present in the intestine at birth and passed in the feces after birth, after trypsin and other enzymes from the pancreas have acted on it. The passage of meconium before birth can be a sign of fetal 'distress.
Meconium ileus:  Obstruction of the intestine (ileus) due to overly thick meconium. Meconium ileus results from a deficiency of trypsin and other digestive enzymes from the pancreas, as in cystic fibrosis.
Medial:  1. Pertaining to the middle; in or toward the middle; nearer the middle of the body. Medial is as opposed to lateral. For example, the medial side of the knee is the side closest to the other knee whereas the lateral side of the knee is the outside of the knee. 2. Within a multilayered structure, the center layer. The medial layer of the aorta is the middle layer. For example, necrosis of the medial layer of the aorta may lead to aortic rupture.
Medial collateral ligament (MCL) of the knee:  The knee joint is surrounded by a joint capsule with ligaments strapping the inside and outside of the joint (collateral ligaments) as well as crossing within the joint (cruciate ligaments). These ligaments provide stability and strength to the knee joint. These ligaments provide stability and strength to the knee joint. The medial collateral ligament of the knee is on the inner side of the joint.
Medial meniscus of the knee:  The word “meniscus” refers to a crescent-shaped cartilaginous structure. The medial meniscus of the knee is a thickened crescent-shaped cartilage pad between the two joints formed by the femur (the thigh bone) and the tibia (the shin bone). The meniscus acts as a smooth surface for the joint to move on. The medial meniscus is toward the inner side of the knee joint.
Median:  The middle, as in the median strip in a highway. For example, the median nerve is the nerve the runs through the middle of the wrist.
Mediastinoscopy:  A procedure in which the physician inserts a tube into the chest to view the organs in the mediastinum. The tube is inserted through an incision above the breastbone.
Mediastinum:  The area between the lungs. The organs in the mediastinum include the heart and its large veins and arteries, the trachea, the esophagus, the bronchi, and lymph nodes.
Medic Alert:  A bracelet that a person wears to warn medical professionals in an emergency about a serious health problem.
Medical College Admissions Test (MCAT):  The MCAT is a test that is required of all applicants to medical school in the U.S. and Canada. The MCAT is “a standardized test used to assess applicants' science knowledge, reasoning, and communication and writing skills.” The MCAT is given under the aegis of the Association of American Medical Colleges.
Medical device:  1. Broadly, any physical item used in medical treatment, from a cardiac pacemaker to a wheelchair.
Medical entomology:  The branch of science that deals with insects that cause disease or that serve as vectors of organisms that cause disease in humans.
Medical geography:  An area of health research that is a hybrid between geography and medicine dealing with the geographic aspects of health and healthcare. Medical geography studies the effects of locale and climate upon health. It aims to improve the understanding of the various factors which affect the health of populations and hence individuals.
Medical helminthology:  The field of medicine that pertains to helminths (worms) capable of disease in people. The public health impact of medical helminths is appreciable. Two billion people are infected by soil-transmitted helminths such as Ascaris, hookworms, and Trichuris trichiura and by schistosomes. Early childhood infections by soil-transmitted helminths delays physical and cognitive development.
Medical jurisprudence:  The branch of the law that deals with the application of law to medicine or, conversely, the application of medical science to legal problems.
Medical physics:  The science of human health and radiation exposure. Medical physics, also called health physics, is devoted to radiation safety.
Medical student syndrome:  A form of acute hypochondriasis that affects most people in training to be a physician. For example, when studying Hodgkin's disease, a medical student feels behind his or her ears or neck, feels little lymph nodes (that are entirely normal), and thinks OMG Hodgkin's disease! (This describes perfectly my experience as a third year medical student.)
Mediterranean anemia (aka thalassemia, beta thalassemia or thalassemia major):  Thalassemia is not just one disease. It is a complex contingent of inherited disorders all of which involve underproduction of hemoglobin, the indispensable molecule in red blood cells that carries oxygen. The globin part of normal adult hemoglobin is made up of 2 alpha and 2 beta polypeptide chains. In beta thalassemia, there is a mutation in both beta globin chains leading to underproduction or absence of beta chains, therefore underproduction of hemoglobin, and profound anemia. The gene for beta thalassemia is relatively frequent in people of Mediterranean origin (for example, from Italy and Greece). Children with this disease inherit one gene for it from each parent. The parents are carriers (heterozygotes) with just one thalassemia gene, are said to have thalassemia minor, and are essentially normal. Their children affected with beta thalassemia seem entirely normal at birth because at birth we still have predominantly fetal hemoglobin which does not contain beta chains. The anemia surfaces in the first few months after birth and becomes progressively more severe leading to pallor and easy fatiguability, failure to grow, bouts of fever (due to infections) and diarrhea. Treatment based on blood transfusions is helpful but not curative. Gene therapy will, it is hoped, be applicable to this disease.
Mediterranean diet:  A diet traditionally followed in Greece, Crete, southern France, and parts of Italy that emphasizes fruits and vegetables, nuts, grains, olive oil (as opposed to butter) and grilled or steamed chicken and seafood (as opposed to red meat). Plus a glass or two of red wine. There is not merely one Mediterranean diet. What is eaten varies significantly from one Mediterranean country to another. There also are major differences in diet between some regions within a country, as in Italy. However, the shared features of what is usually spoken of as the Mediterranean-style diet are as follows: high consumption of fruits, vegetables, bread and other cereals, beans, nuts and seeds; olive oil is the key monounsaturated fat source; dairy products, fish and poultry are consumed in low to moderate amounts; little red meat is eaten; eggs are eaten zero to four times a week; and wine is drunk in moderate (or low) amounts. Many studies indicate that a Mediterranean diet may play an important role in the prevention of coronary artery heart disease. A Mediterranean-style diet also appears to help avoid the metabolic syndrome (prediabetes) and reduce the chances that a person will die sooner rather than later.
Mediterranean Fever:   A inherited disorder of unknown cause featuring short recurring bouts of fever together with pain in the joints, chest or abdomen. Also called Familial Mediterranean Fever (FMF). Between attacks, the patient seems healthy (when FMF is more difficult to diagnose). The gene for FMF was reportedly identified in 1997. FMF is found in persons of Mediterranean ethnic background.
Medulla:  The innermost part. For example, the adrenal medulla is the innermost part of the adrenal gland, the renal medulla is the inner part of the kidney, and the spinal medulla is the part of the spinal cord that is lodged deep within the vertebral canal.
Medulla oblongata:  The base of the brain, which is formed by the enlarged top of the spinal cord. The medulla oblongata directly controls breathing, blood flow, and other essential functions.
Medullary cystic kidney disease, autosomal recessive:  A childhood genetic kidney disease in which there is progressive symmetrical destruction of the kidneys involving both the tubules and glomeruli, characteristically resulting in anemia, polyuria, polydipsia, isosthenuria (decreased ability to concentrate the urine), progressive renal failure and death in uremia. Hypertension and proteinuria are conspicuous by their absence. The chronic kidney failure affects growth and leads to short stature. The age at death ranges from around 4 to 15 years. The disease is also called nephronophthisis 1 (NPH1) and familial juvenile nephronophthisis (FJN). It is inherited as an autosomal recessive trait. It was first described by Guido Fanconi and his colleagues in 1951.
Medulloblastoma:  A type of brain tumor that tends to occur in children, arise in the cerebellum (part of the brain responsible for coordination), and spread along the spine. Medulloblastoma is the most common type of primary brain tumor in childhood. Medulloblastomas occasionally metastasize outside the central nervous system, usually to bone. Treatment involves surgery, radiotherapy, and chemotherapy.
Megacolon:  An abnormally enlarged colon. Megacolon can arise as a serious congenital problem in the newborn, caused by abnormal innervation of the colon and frequently requiring surgery.
Megakaryocyte:  A giant cell in the bone marrow out of which blood platelets are formed, which are essential to normal blood clotting.
Megalencephaly:  Also called macrencephaly, a condition in which there is an abnormally large, heavy, and usually malfunctioning brain. By definition, the brain weight is greater than average for the age and gender of the child. Head enlargement may be evident at birth or the head may become abnormally large in the early years of life. Children with megalencephaly may have delayed development, convulsive disorders, corticospinal (brain cortex and spinal cord) dysfunction, and seizures. Megalencephaly affects males more often than females.
Meibomian cyst:  An inflammation of the oil gland of the eyelid. Also known as chalazion or tarsal cyst.
Meibomian gland:  Also known as the palpebral gland, tarsal gland, or tarsoconjunctival gland. A type of gland in the eyelids that makes a lubricant called sebum which is discharged through tiny openings in the edges of the lids. In the case of underproduction of sebum, one develops dry eye syndrome.
Meibomianitis:  Inflammation of the little glands in the tarsus of the eyelids. Chronic inflammation of these glands can lead to a lump in the eyelid known as a chalazion. Also known as meibomitis.
Meiosis:  The process chromosomes undertake during germ-cell formation (egg + sperm) to halve the chromosome number from 46 to 23 and combine with the corresponding egg or sperm to recreate a new cell with 46 chromosomes, half from egg, half from sperm. As division continues two new cells are created. If the new cell is to be female X chromosomes pair; if to be male the X and Y chromosomes pair.
Meiotic drive:  Preferential selection during meiosis (germ cell production). In meiotic drive there is preferential production of certain gametes. This alters the segregation of genes from the Mendelian expectations. Meiotic drive is a mechanism for transmission distortion. In other words the final genome of the new animal is not a simple statistical dice roll for which genes are included.
Meiotic nondisjunction:  Failure of two members of a chromosome pair to separate from one another during meiosis, causing both chromosomes to go to a single daughter cell. Meiotic nondisjunction is responsible for the extra chromosome 21 in trisomy 21 (Down syndrome) and for extra and missing chromosomes that cause other birth defects and many miscarriages.
Melan- (prefix):  Prefix meaning dark or black. It comes from the Greek "melas", black. Examples of terms containing melan- include melancholia, melanin, melanocytes, melanoma and melena.
Melancholia:  An old term for depression.
Melanin:  The pigment that gives human skin, hair, and eyes their color. Dark-skinned people have more melanin in their skin than light-skinned people have. Melanin is produced by cells called melanocytes. It provides some protection again skin damage from the sun, and the melanocytes increase their production of melanin in response to sun exposure. Freckles, which occur in people of all races, are small, concentrated areas of increased melanin production. Protection from the sun comes at a cost however. Increased melanin means a reduction of vitamin D production. So-called "old age spots" occur when melanocytes burst and release their malanin content which creates a permanent stain in the skin.
Melanocyte:  A cell in the skin that produces and contains the pigment melanin.
Melanoderma:  Various forms of increased skin pigmentation (darkening of the skin). This is directly due to an increased amount of melanin pigment in the skin when there is increased production of melanin by the melanocytes (the cells that make melanin) or if there is a rise in the number of melanocytes.
Melanoma:  The most dangerous form of skin cancer, a malignancy of the melanocyte, the cell that produces pigment in the skin. Melanoma is most common in people with fair skin, but can occur in people with all skin colors. Most melanomas present as a dark, mole-like spot that spreads and, unlike a mole, has an irregular border. The tendency toward melanoma may be inherited, and the risk increases with overexposure to the sun and sunburn. Fair-skinned people and people with a family history of melanoma should always use a high-SPF sunscreen when outdoors. Everyone who has concern about an unusual mole-like spot should see their doctor. Detected early, melanoma is almost always treatable. Undetected, melanoma can spread rapidly and be fatal. People with a history of skin cancer of any kind should have periodic visual exams by a dermatologist.
Melanoma thickness:  A method for determining the prognosis of melanomas. The thickness of a melanoma is related to the 5-year survival rate after surgical removal of the tumor. Also called Breslow thickness, named for the physician Alexander Breslow who in 1975 observed that as the thickness of the tumor increases, the chance of survival goes down.
Melanoma types:  juvenile, acral-lentiginous, amelanotic, benign, choroidal, ciliary body. conjunctival, eye, intraocular, iris, lentigo maligna, malignant, nodular, ocular, superficial spreading, and uveal.
Melanoma vaccine:  A cancer vaccine prepared from human melanoma cancer cells. It may be used alone or with other therapy in treating melanoma.
Melanosis coli:  A benign, reversible condition usually, but not always, associated with long-term use of anthranoid laxatives in which pigment deposition in the lamina propria of the large intestine results in a brown to black discoloration of the lining of the large intestine. Melanosis coli is sometimes called pseudomelanosis coli since the pigment deposited is lipofuscin and not melanin as the name implies. Melanosis coli produces no symptoms and is indicative of chronic anthranoid (senna) laxative use.
MELAS syndrome:  Mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes syndrome, a rare form of dementia caused by mutations in the genetic material (DNA) in the mitochondria.
Melasma:  Pigmentation of the cheeks of the face (malar area). When it occurs during pregnancy it is referred to as chloasma or the mask of pregnancy. Melasma darkens with sun exposure.
Melatonin:  A hormone that is produced by the pineal gland and is intimately involved in regulating the sleeping and waking cycles, among other processes.
MELD:  Acronym for Model End Stage Liver Disease. A disease severity scoring system for adults with liver disease, designed to improve the organ allocation in transplantation based on the severity of liver disease rather than the length of time on the waiting list. The MELD score is based only on laboratory data in order to be as objective as possible.
Melena:  Stool or vomit that is stained black by blood pigment or dark blood products.

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