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Dr. Kennedy's Vocabulary Course: -L-
(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

- L -
(A B C D E F G H I J K L M)
L1-L5 (lumbar vertebrae):  The symbols L1 through L5 represent the five lumbar vertebrae. The lumbar vertebrae are situated between the thoracic vertebrae and the sacral vertebrae in the spinal column.
LAAM:  Levo-alpha acetyl methadol, an alternative to methadone that blocks the effects of opiates for up to 72 hours in the treatment of addiction to heroin and other opiates.
Labia:  The lips, either the lips around the mouth (the oral labia) or the lip-like external female genitalia (the labia majora and labia minora).
Labia majora:  The larger (major) outside pair of labia (lips) of the vulva (the female external genitalia).
Labia minora:  The smaller (minor) inside pair of labia (lips) of the vulva (the female external genitalia).
Labial herpes:  A small sore situated on the face or in the mouth that causes pain, burning, or itching before bursting and crusting over. The favorite locations are on the lips (the labia), chin or cheeks and in the nostrils. Less frequented sites are the gums or roof of the mouth (the palate). Labial herpes is also called fever blisters or cold sores. It is caused by herpes simplex virus type 1. The virus lies latent (dormant) in the body and is reawakened (reactivated) by factors such as stress, sunburn, or fever from a wide range of infectious diseases including colds. Recurrences are less common after age 35.
Labile:  Unstable, unsteady, not fixed. In psychology or psychiatry, labile denotes free and uncontrolled moods or behaviors expressing emotions. In biochemistry, labile means easily removable as, for example, a labile hydrogen molecule. In the context of diabetes, labile is a term used when a diabetic person's blood glucose (sugar) level often swings quickly and widely from high to low and from low to high. Also called brittle and unstable diabetes or type I diabetes. Labile comes from the Latin labilis, meaning liable to slip.
Labile diabetes:  A type of diabetes when a person's blood glucose (sugar) level often swings quickly from high to low and from low to high. Also called "unstable diabetes" or "brittle diabetes."
Lability:  The state or quality of being labile: susceptible to change, error or instability.
Labium:  A lip. Labium is the singular of the Latin neuter noun meaning lip. The plural is labia.
Labor:  Childbirth, the aptly-named experience of delivering the baby and placenta from the uterus to the vagina to the outside world. There are two stages of labor. During the first stage (called the stage of dilatation), the cervix dilates fully to a diameter of about 10 cm. In the second stage (called the stage of expulsion), the baby moves out through the cervix and vagina to be born.
Labra:  The plural of labrum, a ring of fibrocartilage (fibrous cartilage) around the edge of the articular (joint) surface of a bone.
Labrocyte:  A mast cell.
Labrose:  Thick-lipped or large-lipped. Having thick or large lips. From the Latin labrosus, from labrum meaning lip.
Labrum:  In medicine, a ring of fibrocartilage (fibrous cartilage) around the edge of the articular (joint) surface of a bone. The term labrum is used in anatomy to designate a lip, edge, or brim. For example the glenoid labrum is a ring of fibrocartilage that runs around the cavity of the scapula (wingbone) in which the head of the humerus (the bone in the upper arm) fits. The labrum deepens this cavity (the glenoid cavity) and effectively increases the surface of the shoulder joint.
Labyrinth:  The maze of canals in the inner ear. The labyrinth is the portion of the ear that is responsible for sensing balance. Inflammation of the labyrinth (labyrinthitis) can be accompanied by vertigo.
Labyrinthitis:  Inflammation of the labyrinth, the system of intercommunicating canals and cavities within the inner ear responsible for sensing balance. Labyrinthitis may be accompanied by the sudden onset of a feeling of vertigo triggered by head or body movement together with feelings of nausea and malaise.
LAC encephalitis:  LaCrosse encephalitis, one of the main types of encephalitis caused by an arbovirus in the US. An arbovirus is a virus that is arthropod-borne (carried by a mosquito, tick or another kind of arthropod). The arbovirus infects and inflames the brain. LAC encephalitis was first found in a 4-year-old in LaCrosse, Wisconsin in 1963.
Laceration:  A cut.
Lacrimal:  Pertaining to tears, as in lacrimal gland (tear gland).
Lacrimal gland:  A small almond-shaped structure that produces tears. The lacrimal gland is located just above the outer corner of the eye. The lacrimal gland is part of the lacrimal apparatus, the system that forms tears, conveys them through the lacrimal (tear) duct to the eye, and drains the tears.
Lacrimation:  The production, secretion, and shedding of tears.
LaCrosse encephalitis:  One of the main types of encephalitis caused by an arbovirus in the US. An arbovirus is a virus that is arthropod-borne (carried by a tick or another kind of arthropod; LaCrosse encephalitis: One of the main types of encephalitis caused by an arbovirus in the US. An arbovirus is a virus that is arthropod-borne (carried by a mosquito, tick or another kind of arthropod). Mosquitos are insects but also carry LAC). The arbovirus infects and inflames the brain. LaCrosse (LAC) encephalitis was first found in a 4-year-old in LaCrosse, Wisconsin in 1963.
Lactase:  Enzyme that breaks down the milk sugar lactose into glucose and galactose. Persons with a deficiency of lactase in the gut can develop abdominal cramping and diarrhea after ingesting milk products.
Lactase deficiency:  Not enough of an enzyme called lactase in the small intestine to digest lactose, a prominent component of milk and most other dairy products. Lactose is sometimes also used as an ingredient in other foods, so anyone with lactase deficiency should check food labels with care. Most people are born with the ability to make adequate amounts of lactase, but lactase production tends normally to go down with age, more so in some persons than others. There are significant differences in lactase production among different ethnic groups. Inadequate lactase production can cause difficulty digesting lactose-containing products, which include dairy products themselves and any foods containing dairy products as ingredients. The most common symptoms of lactase deficiency are diarrhea, bloating, and gas. The diagnosis of lactase deficiency may be made by a trial of a lactose-free diet or by special testing.
Lactate dehydrogenase:  (LDH) An enzyme that catalyzes the conversion of lactate to pyruvate. This is an important step in energy production in cells. Many different types of cells in the body contain this enzyme. Some of the organs relatively rich in LDH are the heart, kidney, liver, and muscle. As cells die, their LDH is released and finds its way into the blood. Normal LDH levels vary with age, being higher in childhood due to bone growth. Analysis of LDH has not been standardized and normal ranges vary greatly between laboratories. Generally, the upper limit of normal for adults is in the range of 200 units/liter. Nearly every type of cancer, as well as many other diseases, can cause LDH levels to be elevated. Therefore, this marker cannot be used to diagnose a particular type of cancer. LDH levels can be used to monitor treatment of some cancers, including testicular cancer, Ewing's sarcoma, non-Hodgkin's lymphoma, and some types of leukemia. Elevated LDH levels can be caused by a number of noncancerous conditions, including heart failure, hypothyroidism, anemia, and lung or liver disease.
Lactation:  The process of milk production. Human milk is secreted by the mammary glands, which are located within the fatty tissue of the breast. The hormone oxytocin is produced in response to the birth of a new baby, and it both stimulates uterine contractions and begins the lactation process. For the first few hours of nursing, a special fluid called colostrum is delivered, which is especially high in nutrients, fats, and antibodies to protect the newborn from infection. Thereafter the amount of milk produced is controlled primarily by the hormone prolactin, which is produced in response to the length of time the infant nurses at the breast.
Lactic acidosis:  Acidosis (too much acid in the body) due to the buildup of lactic acid in the body. Lactic acidois occurs when cells make lactic acid (from glucose) faster than it can be metabolized. The key signs of lactic acidosis include unusually deep and rapid breathing, vomiting, and abdominal pain. Lactic acidosis is a feature of different disorders. It is an important sign of diabetes that is out of control. It is also a rare but dreaded adverse reaction from the drug metformin (Glucophage) for type 2 diabetes.
Lactobacillus:  A bacterium normally found in the mouth, intestinal tract, and vagina. Lactobacillus can also live in fermenting products, such as yogurt. Humans appear to have a symbiotic relationship with this bacteria. Lactobacillus has been with us so long that some types have become an important part of food digestion, although Lactobacillus can also contribute to cavities in the teeth if allowed to remain too long within the mouth.
Lactobacillus acidophilus:  The bacteria found in milk and fermented milk products, particularly yogurt with "live cultures" of L. acidophilus. L. acidophilus assists with the digestive process within the intestinal tract. It can be decimated by the use of antibiotics, and many health professionals urge people to use probiotics to counter this unfortunate side effect of antibiotic use.
Lactose:  The sugar found in milk. Lactose is a large sugar molecule that is made up of two smaller sugar molecules, glucose and galactose. In order for lactose to be absorbed from the intestine and into the body, it must first be split into glucose and galactose. The glucose and galactose are then absorbed by the cells lining the small intestine. The enzyme that splits lactose into glucose and galactose is called lactase, and it is located on the surface of the cells lining the small intestine.
Lactose intolerance:  Inability to digest lactose, a component of milk and most other dairy products. Lactose is sometimes also used as an ingredient in other foods, so those with a lactase deficiency should check labels carefully. The basis for this condition is lack of an enzyme called lactase in the small intestine. Lactase is essential to digest lactose. Without enough lactase, there is lactose intolerance.Most people are born with the ability to make adequate amounts of lactase, but lactase production normally decreases with age, more so in some persons than others. There are significant differences relative to lactase production among ethnic groups. Lactose intolerance is more prevalent among people of Middle Eastern descent. Inadequate lactase production can cause difficulty digesting lactose-containing products, which include dairy products themselves and foods containing dairy products as ingredients. The most common symptoms of lactase deficiency are diarrhea, bloating, and gas. The diagnosis may be made by a trial of a lactose-free diet or by special testing. In some cases, other diseases of the intestine may need to be excluded by further medical evaluation.
Lacuna:  A small pit, cavity, defect or gap.
LAMB syndrome:  Acronym for Lentigines, Atrial myxomas, Mucocutaneous myxomas, and Blue nevi. Now included in the Carney complex.
Lambert-Eaton myasthenic syndrome:  An autoimmune disease characterized by weakness and fatigue of the proximal muscles (those near the trunk), particularly the muscles of the pelvic girdle (the pelvis and hips) and the thighs, with relative sparing of eye and respiratory muscles. Lambert-Eaton myasthenic syndrome (LEMS) is associated in 40% of cases with cancer, most often with small cell cancer of the lung and less often with other tumors. The neuromuscular defect in LEMS is due to insufficient release of the neurotransmitter acetylcholine by nerve cells. Unlike myasthenia gravis, as muscle contractions continue, strength increases in LEMS. The disease is named for Lambert and Eaton who (together with Rooke) described it in 1966. The disease had actually been reported by Anderson and coworkers in 1953 in a man with oat cell cancer of the lung.
Lamella:  A thin leaf, plate, disk, wafer.
Lamina:  A plate or layer. For example, the lamina arcus vertebrae, usually just called the lamina, are plates of bone in each vertebral body.
Laminaria:  A small rod-shaped piece of dried seaweed; when placed within the cervix, a laminaria causes it to gradually dilate (widen). The species of seaweed serving this purpose is Laminaria digitata.
Laminectomy:  A surgical procedure in which the posterior arch of a vertebra is removed. Laminectomy is done to relieve pressure on the spinal cord or on the nerve roots that emerge from the spinal canal. The procedure may be used to treat a slipped or herniated disk or to treat spinal stenosis.
Laminopathy:  A disease due to mutation of the lamin A/C gene. The laminopathies include: Emery-Dreifuss muscular dystrophy type 2, familial partial lipodystrophy, limb girdle muscular dystrophy type 1B, dilated cardiomyopathy, familial partial lipodystrophy, Charcot-Marie-Tooth disorder type 2B1, mandibuloacral dysplasia, childhood progeria syndrome (Hutchinson-Gilford syndrome) and a subset of Werner syndrome.
Lancet:  A small pointed knife; a surgical instrument with a short, wide, sharp-pointed, two-edged blade; a little knife with a small point. Lancets are used today to prick the skin (a finger, foot, ear lobe, etc.) to obtain a small quantity of capillary blood for testing.
Landau-Kleffner syndrome:  A disorder with seizures starting in childhood in which the patient loses skills, such as speech, and develops behavior characteristic of autism. A major feature of the Landau-Kleffner syndrome (LKS) is the gradual or sudden loss of the ability to understand and use spoken language. LKS occurs most frequently in normally developing children who are between 3 and 7 years of age. For no apparent reason, these children begin having trouble understanding what is said to them. Doctors often refer to this problem as auditory agnosia or "word deafness." The inability to understand language eventually affects the child's spoken language which may progress to a complete loss of the ability to speak (mutism).
Landry ascending paralysis:  A particularly virulent form of Guillain-Barre syndrome. The disorder often begins with a flu-like illness that brings on general physical weakness, but is then characterized by rapidly progressing paralysis that starts in the legs and arms, and may move on (ascend) to affect the breathing muscles and face. As with less severe forms of Guillain-Barre, the exact cause is not yet known but presumed to be viral and/or autoimmune.
Lansing virus:  Type 2 poliovirus. Named after the city in Michigan where the first patient lived who was found to have this virus. There are two other strains of poliovirus.
Lanugo:  Downy hair on the body of the fetus and newborn baby. It is the first hair to be produced by the fetal hair follicles, usually appearing on the fetus at about five months of gestation. It is very fine, soft, and usually unpigmented. Although lanugo is normally shed before birth around seven or eight months of gestation, it is sometimes present at birth. This is not a cause for concern: lanugo will disappear within a few days or weeks of its own accord.
Laparoscope:  An instrument through which structures within the abdomen and pelvis can be seen.
Laparoscopic assisted vaginal hysterectomy:   A procedure using laparoscopic techniques to remove the uterus (womb) and/or tubes and ovaries through the birth canal. Laparoscopic assisted vaginal hysterectomy is often referred to as LAVH.
Laparoscopic cholecystectomy:  Removal of the gallbladder (cholecystectomy) by laparoscopy.
Laparoscopic staging:  A staging procedure for tumors of the abdomen using laparoscopy in combination with laparoscopic ultrasonography. The aim of laparoscopic staging is to prevent unnecessary laparotomies and avoid the trauma inherent in open surgery on the abdomen while providing accurate information on tumor spread to permit effective treatment. The treatment of tumors such as pancreatic cancer, malignancy of the liver, gastrointestinal cancer, ovarian cancer, and lymphoma can be based on laparoscopic staging. Laparoscopic staging also enables palliative procedures to be performed during the staging procedure.
Laparoscopy:  A type of minimally invasive surgery in which a small incision (cut) is made in the abdominal wall through which an instrument called a laparoscope is inserted to permit structures within the abdomen and pelvis to be seen. The abdominal cavity is distended and made visible by the instillation of absorbable gas, typically, carbon dioxide.
Laparotomy:  An operation to open the abdomen. The word is compounded from Greek roots lapara referring to the soft parts of the body between the rib cage and the hips and tome meaning "a cutting."
Large cell carcinoma:  A group of lung cancers in which the cells are large and look abnormal, in distinction to small cell carcinoma (aka oat cell carcinoma).
Large saphenous vein:  The larger of the two saphenous veins, the principal veins that run up the leg superficially (near the surface). The large saphenous vein goes from the foot all the way up to the saphenous opening, an oval aperture in the broad fascia of the thigh, a fibrous membrane through which the vein passes. The other saphenous vein, termed (not too surprisingly) the small saphenous vein, runs behind the outer malleolus (the protuberance on the outside of the ankle joint), comes up the back of the leg and joins the popliteal vein in the space behind the knee (the popliteal space). The large saphenous vein is also called the great saphenous vein.
Large-cell lymphoma:  Cancer of the lymphatic tissue that is characterized by unusually large cells.
Laribacter hongkongensis:  A novel type of bacterium first isolated in Hong Kong in 2001 from the blood and empyema (pus in the chest) of a man with alcoholic cirrhosis. Laribacter hongkongensis has been associated with (but not yet proven to cause) community-acquired gastroenteritis and traveler's diarrhea. Risk factors for infection include consumption of fish and minced freshwater fish meat.
Laryngeal:  Having to do with the larynx (the voice box).
Laryngeal dysphonia:  A voice disorder caused by involuntary movements of one or more muscles of the larynx or voice box. People who have spasmodic dysphonia may have occasional difficulty saying a word or two or they may experience sufficient difficulty to interfere with communication. Laryngeal dysphonia causes the voice to break or to have a tight, strained, strangled or effortful quality. Spasmodic dysphonia can affect anyone. It most often becomes evident between 30 and 50 years of age. More women are affected by laryngeal dysphonia than men. Also called spastic dysphonia and spasmodic dystonia.
Laryngeal framework surgery:   A surgical technique designed to improve the voice by altering the cartilages of the larynx (the voice box), which houses the vocal folds (the vocal cords) in order to change the position or length of the vocal folds. Laryngeal framework surgery is also called thyroplasty.
Laryngeal nerve palsy:  Paralysis of the larynx (voice box) caused by damage to the recurrent laryngeal nerve or its parent nerve, the vagus nerve, which originates in the brainstem and runs down to the colon. The recurrent laryngeal nerve supplies the larynx (voice box). The larynx will be paralyzed on the side where this nerve has been damaged, unless the problem originated with damage to the vagus nerve itself. Damage to the recurrent laryngeal nerve can result from diseases inside the chest, such as a tumor, an aneurysm of the arch of the aorta, or an aneurysm of the left atrium of the heart.
Laryngeal papilloma:  A warty growth in the larynx, usually on the vocal cords. Persistent hoarseness is a common symptom.
Laryngeal papillomatosis:  Laryngeal papillomatosis is the growth of numerous warty growths on the vocal cords. The disease is most common in young children. Laryngeal papillomatosis can be due to the baby contracting human papilloma virus (HPV) during birth through the vaginal canal from a mother with genital warts (which are due to HPV). Each year, about 300 infants are born with the virus on their vocal cords because of maternal transmission. Recurrences of laryngeal papillomatosis are frequent. Remission may occur after several years.
Laryngeal stenosis:  Narrowing or constricting of the larynx, the voice box.
Laryngectomy:  Surgery to remove part or all of the larynx is a partial or total laryngectomy. In either operation, the surgeon performs a tracheostomy, creating an opening called a stoma in the front of the neck. (The stoma may be temporary or permanent). Air enters and leaves the trachea and lungs through this opening. A tracheostomy tube, also called a trache ("trake") tube, keeps the new airway open. A partial laryngectomy preserves the voice. The surgeon removes only part of the voice box, just one vocal cord, part of a cord, or just the epiglottis, and the stoma is temporary. After a brief recovery period, the trache tube is removed, and the stoma closes up. The patient can then breathe and talk in the usual way. In some cases, however, the voice may be hoarse or weak. In a total laryngectomy, the whole voice box is removed, and the stoma is permanent. The patient, called a laryngectomee, breathes through the stoma. A laryngectomee must learn to talk in a new way.
Laryngitis:  Laryngitis is an inflammation of the larynx, the portion of the airway (respiratory tract) containing the vocal cords. The larynx is about two inches long and is located between the pharynx and the trachea. Its outer wall consists of cartilage and forms the structure we refer to as the "Adam's apple." Since the vocal cords are contained within the larynx, people with laryngitis often speak hoarsely or may be unable to speak louder than a whisper. Inflammation of the larynx is most often caused by viral infections. In these cases, other symptoms, such as sore throat, cough, difficulty swallowing, and fever generally occur. The voice changes may persist after the fever and other symptoms of acute infection have resolved. Laryngitis can also occur as a result of irritation to the vocal cords. People such as singers, cheerleaders, or small children after bouts of screaming may find that they become hoarse or speak with a "gravelly" voice after prolonged overuse. Environmental causes of irritation of the airway that can result in inflammation of the larynx include exposure to tobacco smoke or other chemicals.
Laryngomalacia:  A soft floppy larynx (voice box).
Laryngoscope:  A flexible, lighted tube used to look at the inside of the larynx (the voice box). The laryngoscope is inserted through the mouth into the upper airway.
Laryngostasis:   More commonly known as croup, this is an infection of the larynx, trachea, and the bronchial tubes, that occurs mainly in children. It is usually caused by viruses, less often by bacteria. Symptoms include a cough that sounds like a barking seal and a harsh crowing sound during inhaling.
Laryngotomy:  Surgical opening of the larynx, the voice box.
Larynx:  The larynx is the portion of the breathing, or respiratory, tract containing the vocal cords which produce vocal sound. It is located between the pharynx and the trachea. The larynx, also called the voice box, is a 2-inch-long, tube-shaped organ in the neck.
Larynx transplant:  A transplant of the larynx, or voicebox. This procedure permits a human-sounding voice with inflection, range, and qualities unique to the patient, and normal swallowing. The risks of the procedure include those of organ rejection and immunosuppression therapy.
Laser:  A powerful beam of light that can produce intense heat when focused at close range. Lasers are used in medicine in microsurgery, cauterization, for diagnostic purposes, etc. For example, lasers are employed in microsurgery to cut tissue and remove tissue. A laser concentrates high energies into an intense narrow beam of nondivergent monochromatic electromagnetic radiation; Lasers using various substances (ruby, argon, krypton, neodymium, helium-neon, carbon dioxide) are available. Laser is an acronym coined in 1960 from a forgettable term: Light Amplification by Stimulated Emission of Radiation.
Laser coagulation:  The coagulation (clotting) of tissue using a laser. A coagulation laser produces light in the visible green wavelength that is selectively absorbed by hemoglobin, the pigment in red blood cells, in order to seal off bleeding blood vessels.
Laser surgery:  A type of surgery that uses the cutting power of a laser beam to make bloodless cuts in tissue or remove a surface lesion such as a skin tumor. There are a number of different types of lasers that differ in emitted light wavelengths and power ranges and in their ability to clot, cut, or vaporize tissue. Among the commonly used lasers are the pulsed-dye laser, the YAG laser, the CO2 (carbon dioxide) laser, the argon laser, the excimer laser, the KTP laser, and the diode laser.
Laser-assisted in situ keratomileusis:  A kind of laser eye surgery designed to change the shape of the cornea to eliminate or reduce the need for glasses and contact lenses in cases of severe myopia (nearsightedness). The procedure is best known as LASIK, an acronym for laser-assisted in situ keratomileusis (Latin/Greek for "in place cornea carving").
Lassa fever:  An acute viral infection found in the tropics, especially in West Africa. Epidemics of Lassa fever have occurred in countries such as Sierra Leone, Congo (formerly Zaire), Liberia and Nigeria. The disease was discovered in 1969 when two missionary nurses died of it in the village of Lassa, Nigeria. The virus is an arenavirus, a single-stranded RNA virus that is animal-borne (zoonotic). Lassa fever is a grave health concern because it can cause a very severe potentially fatal illness, is highly contagious and can spread like wildfire.
Lassitude:  Weakness, weariness, listlessness, exhaustion, lethargy. For example, the patient complained of lassitude. Borrowed from French, from Latin lassitudo, from lassus meaning weary.
Late infantile neuroaxonal dystrophy:  (aka Hallervorden-Spatz disease) A genetic disorder in which there is progressive neurologic degeneration with the accumulation of iron in the brain.
Latent:  Hidden, dormant, inactive. For example, the virus that causes chickenpox remains latent after the initial attack of chickenpox is over. When it becomes reactivated, usually many years later, the virus causes shingles. Another example: HIV may remain in a small long-lived population of infected T cells in a latent condition.
Lateral:  1. In anatomy, the side of the body or a body part that is farther from the middle or center of the body.
Lateral collateral ligament (LCL) 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 lateral collateral ligament of the knee is on the outside (lateral to the rest of the knee) of the joint.
Lateral epicondylitis:  (aka tennis elbow) A painful injury to the tendon that is attached to the outer part of the elbow due to repetitive twisting of the wrist or forearm which causes irritation and inflammation of the extensor tendon. This tendon attaches to the lateral epicondyle of the humerus. Tennis is not the only culprit. Any action that involves repetitive twisting of the wrist or forearm such as using a screwdriver can lead to this injury.
Lateral femoral cutaneous nerve:  A nerve that supplies sensation to the outer portion of the thigh. Abbreviated LFCN.
Lateral meniscus of the knee:  The word "meniscus" refers to a crescent-shaped structure. The lateral 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 lateral meniscus is toward the outer side of the knee joint.
Lateral ventricle:  One cavity in a system of four communicating cavities within the brain that are continuous with the central canal of the spinal cord. (The four ventricles consist of two lateral ventricles, the third ventricle and the fourth ventricle.)
Lateral X-ray:  An X-ray picture taken from the side.
Latham bowl:  A blood-processing instrument that uses centrifugal force to separate blood into its components: red blood cells, white blood cells, plasma and platelets. Developed by Allen Latham Jr. who had grown up on a farm, so the design "was like a milk separator." The Latham bowl revolutionized the way blood was collected and processed.
Lattice dystrophy:  A form of hereditary corneal dystrophy in which there is an accumulation of amyloid deposits, or abnormal protein fibers, throughout the middle and anterior stroma of the cornea. These deposits in the stroma appear on an eye examination as clear, comma-shaped overlapping dots and branching filaments, creating a lattice effect. Over time, the lattice lines grow opaque and involve more of the stroma. They also gradually converge, giving the cornea a cloudiness that may also reduce vision. These abnormal protein fibers can accumulate under the cornea's outer layer -- the epithelium -- causing it to erode. This condition is known as recurrent epithelial erosion. The may eventually require a corneal transplant but recurrence in the donor cornea can occur within three years. It usually responds well to the eximer laser.
Laughing gas:  Nitrous oxide, a gas that can cause general anesthesia. Nitrous oxide is sometimes given in the company of other anesthetic agents but it is never used today as the only anesthetic agent because the concentration of nitrous oxide needed to produce anesthesia is close to the concentration that seriously lowers the blood oxygen level and creates a hazardous state of hypoxia.
Launois-Bensaude syndrome:  A disorder characterized by painless symmetrical diffuse deposits of fat beneath the skin of the neck, upper trunk, arms and legs.
Lavage:  Washing out. Gastric lavage is washing out the stomach, for example, to remove drugs or poisons.
LAVH (Laparoscopic assisted vaginal hysterectomy):  a procedure using laparoscopic techniques to remove the uterus and/or tubes and ovaries through the vagina.
Laxative:  Something that loosens the bowels. Used to combat constipation (and sometimes overused, producing diarrhea). The word "laxative" comes from the Latin "laxare" meaning "to open, widen, extend, release."
Lay midwife:  A midwife who has entered the profession as an apprentice to a practicing midwife rather than attending a formal school program.
Laying on of hands:  In alternative medicine, an ancient method of healing by touching a person with the hands or palms, usually on the head, shoulders, or waist. Also called contact healing and therapeutic touch.
Lazy eye:  An eye that diverges in gaze. A lazy eye is formally called strabismus. A lazy eye can be due to esotropia (cross-eyed) or to exotropia (wall-eyed). The danger of the condition is that the brain comes in time to rely more on one eye than the other and that part of the brain circuitry connected to the less-favored eye fails to develop properly, leading to amblyopia (blindness) in that eye.
LCHAD deficiency:  Acute fatty liver of pregnancy (AFLP) has been found to be associated in some cases with an abnormality of fatty-acid metabolism. This abnormality is a deficiency of the enzyme long-chain-3-hydroxyacyl-CoA dehydrogenease (LCHAD).
LCL (lateral collateral ligament) of the knee:  The lateral collateral ligament of the knee is on the outside of the joint. 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.
LDH:  Lactate dehydrogenase - an enzyme used to help assess liver health.
LDL (low-density lipoprotein):  A molecule that is a combination of lipid (fat) and protein. Lipoproteins are the form in which lipids are transported in the blood. LDL transports cholesterol from the liver to the tissues of the body. LDL cholesterol is therefore considered the "bad" cholesterol.
Lead poisoning:  An environmental hazard capable of causing brain damage. In the US lead poisoning is formally defined as having at least 10 micrograms of lead per deciliter of blood. (The average level of lead, for people ages 1 to 70, is 2.3 micrograms.) The problem with the toxic heavy metals, of which lead is one, is that 2-3 days after exposure the metals are stored in the lipid storage areas of the body and not accessible to measurement without the use of a "challenging" dose of a chelating agent followed by a urine collection analysis.
Lean body mass:  The mass of the body minus the fat (storage lipid). There are a number of methods for determining the lean body mass. Some of these methods require specialized equipment such as underwater weighing (hydrostatic weighing), BOD POD (a computerized chamber), and DEXA (dual-energy X-ray absorptiometry). Other methods for determining the lean body mass are simple such as skin calipers and bioelectric impedance analysis (BIA).
Learning disability:  A childhood disorder characterized by difficulty with certain skills such as reading or writing in individuals with normal intelligence. Learning disorders affect the ability to interpret what one sees and hears or the ability to link information from different parts of the brain. These limitations can show up in many ways -- as specific difficulties with spoken and written language, coordination, self-control, or attention. Such difficulties extend to schoolwork and can impede learning to read or write, or to do math.
Lecithin:  A generic term to designate any group of yellow-brownish fatty substances occurring in animal and plant tissues, and in egg yolk, composed of phosphoric acid, choline, fatty acids, glycerol, glycolipids, triglycerides, and phospholipids (e.g., phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol).
Lectin:  A complex molecule that contains both protein and sugar. Lectins are made by both animals and plants and are able to bind to the outside of a cell and cause biochemical changes in it.
Leech:  An aquatic parasite that sucks blood from animals. Leeches play a role in medicine today.
Leech therapy:  The use of leeches in medical treatment. Once used as an almost universal cure, leeches were largely abandoned by medicine but in the second half of the 20th century regained some popularity of use. Its role is largely in plastic and reconstructive surgery. Leeches can assist, for example, in the reattachment of severed body parts such as a finger, hand, toe, leg, ear, nose or the scalp. It is believed that the death of President George Washington was caused by the inappropriate use of leeches to treat pneumonia, a common practice in that era.
Left atrium:  The upper left chamber of the heart. The left atrium receives oxygenated blood from the lungs and pumps it down into the left ventricle which delivers it to the body.
Left heart:  The heart is composed functionally of two hearts - the right heart and the left heart. The left heart consists 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.
Left heart hypoplasia syndrome:  A form of congenital heart disease in which the whole left half of the heart (including the aorta, aortic valve, left ventricle and mitral valve) is underdeveloped (hypoplastic). Blood returning from the lungs has to flow through an opening in the wall between the upper chambers of the heart (an atrial septal defect). The right ventricle pumps blood into the pulmonary artery, and blood reaches the aorta through a shunt (the ductus arteriosus) connecting the pulmonary artery with the aorta. The child may seem normal at birth but have trouble within a few days of birth (when the ductus closes), become ashen, have rapid and difficult breathing and have problems feeding. This heart defect is usually fatal within the first days or months of life without treatment, namely a sequence of surgical operations or a heart transplant.
Left hepatic duct:  The duct that drains bile from the left half of the liver and joins the right hepatic duct to form the common hepatic duct.
Left ventricle:  The left lower chamber of the heart that receives blood from the left atrium and pumps it out under high pressure through the aorta to the body
Left ventricular assist device:  A mechanical pump that takes over the function of the damaged ventricle of the heart and restores normal blood flow.
Left ventricular assist devices (LVADs):  These pumps were originally developed for patients with heart disease from which they were not expected to recover and who needed mechanical support as a bridge to a heart transplant. LVADs were then used in patients with heart failure who needed ventricular assistance to allow the heart to rest and recover its function. This permitted a meaningfully longer survival and an improved quality of life. LVADs also provide an alternative treatment for patients with advanced heart failure who are not candidates for cardiac transplantation. The devises cost about $60,000 each in 2003 with an additional $150,000 in hospitalization charges.
Left-handed:  The preferential use of the left hand for most fine manual tasks. Approximately 10% of the population is left-handed. In French, the word for left is gauche meaning clumsy or awkward and the word for right is droit. In Latin the word for left is sinister and that for right is dexter (as in dexterity).
Leg:  In popular usage, the leg extends from the top of the thigh down to the foot. However, in medical terminology, the leg refers to the portion of the lower extremity from the knee to the ankle.
Leg pain with cramping:  An aching, crampy, tired, and sometimes burning pain in the legs that comes and goes -- it typically occurs with walking and goes away with rest -- due to poor circulation of blood in the arteries of the legs. Known medically as intermittent claudication.
Legal blindness:  The criteria used to determine eligibility for government disability benefits and which do not necessarily indicate a person's ability to function. In the US, the criteria for legal blindness are: Visual acuity of 20/200 or worse in the better eye with corrective lenses (20/200 means that a person at 20 feet from an eye chart can see what a person with normal vision can see at 200 feet); or Visual field restriction to 20 degrees diameter or less (tunnel vision) in the better eye. Note that the definition of legal blindness differs from country to country and that the criteria listed above are for the US.
Legal medicine:  The branch of medicine that deals with the application of medical knowledge to legal problems and legal proceedings. Legal medicine is also called forensic medicine.
Legg-Calvé-Perthes disease:  A hip disorder in children due to interruption of the blood supply to the head of the femur (the ball in the ball-and-socket hip joint), causing it to deteriorate. The disease is most common at age 6 to 9, tends to affect boys, but is more severe in girls. It can be familial.
Legionella:  The bacterium that causes Legionnaires' disease. This disease is due specifically to the bacterium Legionella pneumophila found in plumbing, shower heads and water-storage tanks. Outbreaks of Legionella pneumonia have been attributed to evaporative condensers and cooling towers. The bacterium thrives in the mist sprayed from air-conditioning ducts and so it can infest an entire building or airplane. Travelers are especially vulnerable in the closed space within a plane.
Leigh's disease:  A rare genetic disorder characterized by progressive damage to the central nervous system. Leigh's disease is caused by a defect in the function of mitochondria within the cells of the body. Symptoms begin in infancy and include poor sucking ability, the loss of head control and motor skills, loss of appetite, vomiting, irritability, continuous crying, and seizures. As the disorder progresses, symptoms may also include generalized weakness, lack of muscle tone, and episodes of lactic acidosis, which can lead to impairment of respiratory and kidney function. There are different forms of Leigh's disease, but all forms have a poor prognosis. Most cases are fatal during childhood, although some individuals have survived to adolescence. Also known as Leigh's syndrome.
Leiomyoma:  A benign tumor of smooth muscle, the type of muscle that is found in the heart and uterus. A leiomyoma of the uterus is commonly called a uterine fibroid.
Leiomyosarcoma:  A malignant tumor of smooth muscle origin. Smooth muscle is the major structural component of most hollow internal organs and the walls of blood vessels. Can occur almost anywhere in the body but is most frequent in the uterus and gastrointestinal tract. Complete surgical excision, if possible, is the treatment of choice.
Leishmaniasis:  Diseases due to the parasite called Leishmania involving the organs (visceral leishmania aka kala-azar) or the skin plus mucous membranes (espundia), or the skin alone (usually named for the place plus boil, button or sore as, for example, Jericho boil, Bagdad button, Delhi sore). The offending organism is Leishmania donovani which is transmitted by sandfly bites in parts of Asia (primarily India), Africa (primarily Sudan) and South America (primarily Brazil) where all together there are an estimated half million cases per year. There are also several hundred cases yearly in Europe (primarily in the Mediterranean region) and a few in North America.
Lemierre syndrome:  A potentially lethal form of sore throat caused by the bacterium Fusobacterium necrophorum, a common inhabitant of the mouth. This disease vanished with the advent of antibiotics but then returned decades later. It has been called the "forgotten disease."
Lennox syndrome:  A severe form of epilepsy that is characterized by the onset in early childhood of frequent seizures of multiple types, developmental delay, a particular brain wave pattern (a slow spike-and-wave pattern), and behavioral disturbances with poor social skills and attention-seeking behavior.
Lens:  The transparent structure inside the eye that focuses light rays onto the retina (the nerve layer that lines the back of the eye, senses light and creates impulses that go through the optic nerve to the brain). The lens was named after the lentil bean because it resembled it in shape and size.
Lentigo:  A type of freckle that is a small tan, brown, or black spot which tends to be darker than the usual (ephelis-type) freckle and which do not fade in the winter. This kind of spot is referred to as lentigo simplex. Although lentigines may be part of a genetic disorder, for the most part they are just isolated and unimportant spots. (The genetic disorder in which lentigines occur is called Lentiginosis profusa syndrome or Leopard syndrome.) Lentigo is the Latin word for lentil. A lentigo looks like a lentil bean. The plural is lentigines.
Lentigo maligna melanoma:  One of the four clinical types of malignant melanoma and the slowest growing one. It typically begins as a patch of mottled pigmentation that is dark brown, tan, or black on sun-exposed skin, such as on the face.
Lentigo senilis:  A benign pigmented flat spot on sun-exposed skin in older adults, especially on the back of the hands and on the forehead. Also called a liver spot.
Lenz microphthalmia syndrome:  A genetic disorder characterized by microphthalmia (small eye) or anopthalmia (no eye) associated with malformation of the ears, teeth, fingers, skeleton, and genitourinary system. About half of patients have microcephaly (small head) and mental retardation.
LEOPARD syndrome:  A genetic syndrome transmitted in an autosomal dominant manner that is named for its characteristic features: L -- lentigines (dark freckles) on the head and neck E -- electrocardiogram (EKG) abnormalities O -- ocular hyperteleorism (wide-spacing of the eyes) P -- pulmonary stenosis A -- abnormal genitalia R -- retardation of growth D -- deafness (sensorineural type)
Leper:  1. Someone with leprosy (Hansen disease). The term leper is now politically incorrect. 2. By extension, a pariah. A person who is avoided or shunned by society. From the the Greek lepros meaning scaly, referring to the scales that form on the skin in some cases of leprosy.
Leprosy (Hansen's disease):  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. M. leprae is an obligate parasite that has to live within cells. There it is able to withstand the onslaught of enzymes and other forces by virtue of possessing a peculiarly resistant waxy coat and thanks also to its association with lowered cellular immunity. For thousands of years, leprosy was one of the world's most feared communicable diseases, because the skin and nerve damage often led to terrible disfigurement and disability. (In ancient sources such as the Bible, the term "leprosy" was used to describe a number of cutaneous diseases, especially those of a contagious and chronic nature, probably including psoriasis.) The classic clinical form of leprosy is called anesthetic leprosy. It chiefly affects nerves. The condition is marked initially by hyperesthesia (excess sensation) succeeded by anesthesia (lack of feeling) and by paralysis, ulceration, and various other problems, ending horribly in gangrene and self-mutilation. Today leprosy can be cured, particularly if treatment is begun early. The treatment of choice is a multidrug therapy (MDT) using diaphenylsulfone (Dapsone), rifampicin (Rifadin), and clofazimine (Lamprene). Surgery can reconstruct damaged faces and limbs.
Leptin:  A hormone that has a central role in fat metabolism. Leptin was originally thought to be a signal to lose weight but it may, instead, be a signal to the brain that there is fat on the body.
Leptomeninges:  The two innermost layers of tissues that cover the brain and spinal cord. The two layers are called the arachnoid and pia mater (closest to the brain, actually adherent).
Leptospirosis:  An infectious disease caused by a particular type of bacteria called a spirochete transmitted by rats as well as by skunks, opossums, raccoons, foxes, and other vermin. Leptospirosis occurs worldwide but is most commonly acquired in the tropics. About 100 cases of leptospirosis are reported each year in the US. The disease is becoming a greater risk as more people travel to undeveloped areas of the world.
Lesbian:  Female homosexual. The name "lesbian" comes from the Greek island of Lesbos in the Aegian Sea where in antiquity the women were said to be homosexual.
Lesbianism:  Female homosexuality. Also called sapphism (after the lesbian poet Sappho).
Lesion:  Pronounced "lee-sion" with the emphasis on the "lee," a lesion can be almost any abnormality involving any tissue or organ due to any disease or any injury.
Let down reflex:  An involuntary reflex during breastfeeding which causes the milk to flow freely.
Lethal:  Deadly, fatal, capable of causing death, death-dealing. The word "lethal" comes from the Latin "letum" meaning "death or destruction."
Lethal gene, zygotic:  A gene that is lethal (fatal) for the zygote, the cell formed by the union of a sperm (male sex cell) and an ovum (female sex cell). The zygote would normally develop into an embryo, as instructed by the genetic material within the unified cell. However, a zygotic lethal gene scotches prenatal development at its earliest point. A zygotic lethal gene is a mutated (changed) version of a normal gene essential to the survival of the zygote. The extent of the mutation can range from a change in a single base in the DNA to deletion (loss) of the entire gene.
Lethargy:  1. Abnormal drowsiness, stupor. 2. A state of indifference. From the Greek lethargia, drowsiness.
Letrozole:  An oral antiestrogen. Letrozole inhibits the enzyme aromatase in the adrenal glands that produces the estrogens (estradiol and estrone) and thereby lowers their levels. The brand name of letrozole is Femara.
Leucemia:  A different spelling of leukemia, cancer of the blood cells.
Leucine:  An amino acid, one of the 20 building blocks of protein. A dietary essential amino acid, leucine is needed for optimal growth in childhood. It is one of the three branched-chain amino acids. Symbol: Leu.
Leukemoid reaction:  A benign condition in which the high number of white blood cells found in a blood test resembles the numbers seen in leukemia. For example, infectious mononucleosis can return blood-test results with a leukemoid reaction.
Leuko-:   Prefix meaning white, as in leukocyte (white blood cell). Leuko- comes from the Greek "leukos" meaning white.
Leukocoria:  A white pupillary reflex. When one shines a bright light on the pupil, it normally appears red. In leukocoria, the light makes the pupil look white. This occurs with a number of eye diseases including congenital cataract and retinoblastoma (a malignancy of the retina).
Leukocyte count:  A white blood cell (WBC) count.
Leukocytes:  Cells that help the body fight infections and other diseases. Also called white blood cells (WBCs).
Leukocytosis:  Increase in the number of white blood cells.
Leukodystrophy:  A disorder of the white matter of the brain, the part of the brain that contains myelinated nerve fibers. The white matter is white because it is the color of myelin, the insulation covering the nerve fibers. (The white matter is as opposed to the gray matter, the cortex of the brain which contains the nerve cell bodies). The white matter is involved in the conduction of nerve impulses in the brain.
Leukoencephalopathy with vanishing white matter:  An inherited brain disease that occurs mainly in children. and follows a chronic progressive course with additional episodes of rapid deterioration following stress from febrile infection or minor head trauma. Leukoencephalopathy with vanishing white matter (VWM) is due to mutations in either of two genes.
Leukomalacia, cystic periventricular:  Softening of the white matter near the ventricles of the brain resulting in abnormal cysts. Cystic periventricular leukomalacia is a major problem in very premature infants.
Leukopenia:  Lower than the normal amount of white blood cells.
Leukoplakia:  A white spot or patch on the mucous membranes in the mouth (for instance, inside the cheeks, on the gums or the tongue) that may become cancerous.
Leukoreduction:  A process used to filter and remove white blood cells from whole blood before transfusion. The reason why white blood cells (leukocytes) are removed from blood is because they provide no benefit to the recipient but can carry bacteria and viruses to the recipient.
Leukotriene:  One of a group of hormones that cause the symptoms of hay fever and asthma. Derived from arachidonic acid, the leukotrienes act by mediating immediate hypersensitivity. Leukotriene modifiers that prevent the production or action of leukotrienes are used to treat hay fever and asthma.
Levocardia:  Reversal of all of the abdominal and thoracic organs (situs inversus) except the heart, which is still in its usual location on the left. Levocardia virtually always reflects the presence of congenital heart disease (malformation of the heart or great vessels).
Levothyroxine:  A synthetic thyroid hormone used as a thyroid hormone replacement drug (brand names include Eltroxin, Levothroid, Levoxine, Levoxyl, Synthroid) used to treat an underactive thyroid gland (hypothyroidism).
Lhermitte sign:  Sudden transient electric-like shocks extending down the spine triggered by flexing the head forward. Due to a disorder such as compression of the cervical spine (the portion of the spinal cord within the neck). The causes of Lhermitte sign include multiple sclerosis (MS), radiation damage to the spinal cord), cervical spondylosis (degeneration of the disc spaces between the vertebrae), herniation of a cervical disc, a cervical spinal cord tumor, and subacute combined degeneration (caused by vitamin B12 deficiency). Shocks radiating up the spine are sometimes referred to a reverse Lhermitte sign.
LHRH agonist:  A compound that is similar to LHRH (luteinizing hormone-releasing hormone) in structure and is able to act like it. Luteinizing hormone-releasing hormone is a naturally occurring hormone that controls sex hormones in both men and women. Thus, an LHRH agonist serves in a manner similar to LHRH to control the same sex hormones.
Li-Fraumeni syndrome (LFS):  This is an extraordinary cancer family syndrome. People with LFS have a tendency to develop a great diversity of tumors.
Libido:  1. Sexual drive. 2. In psychoanalysis, the psychic energy from all instinctive biological drives. Freud invented the term in 1913.
Lichen planus:  A common skin disease with small itchy pink or purple spots on the arms or legs. The lesions (abnormal areas) on the skin in lichen planus are typically polygonal, flat (hence, the term planus), and pruritic (itchy). Occurs characteristically on the wrists, shins, lower back and genitalia. Involvement of the scalp may lead to hair loss. The cause(s) of lichen planus are unknown. However, it can be triggered by the use of certain drugs (thiazide diuretics, phenothiazines, antimalarials). Treatment is with topical corticosteroids. In most cases, the disease spontaneously regresses 6 months to 2 years after onset.
Lichenification:  Thick, leathery skin, usually the result of constant scratching and rubbing. With prolonged rubbing or scratching, the outer layer of the skin (the epidermis) becomes hypertrophied (overgrown) and this results in thickening of the skin and exaggeration of the normal skin markings, giving the skin a leathery bark-like appearance.
Lichtenberg figures:  A fern-leaf pattern of reddish, painless marks on the skin that are a result of a skin reaction to a lightening strike. The pattern typically vanishes in a few hours or days.
Life support:  A therapy or device designed to preserve someone's life when an essential bodily system is not doing so. Life support may, for example, involve enteric feeding (by a tube), total parenteral nutrition, mechanical ventilation, a pacemaker, defibrillator, heart/lung machine, or dialysis.
Lifestyle disease:  A disease associated with the way a person or group of people lives. Lifestyle diseases include atherosclerosis, heart disease, and stroke; obesity and type 2 diabetes; and diseases associated with smoking and alcohol and drug abuse.
Lifetime risk:  The risk of developing a disease during ones lifetime or dying of the disease. For example the estimated lifetime risk of developing diabetes for individuals born in 2000 in the US is 32.8% for males and 38.5% for females. Women who inherit mutations of the BRCA1 or BRCA2 gene are at an 82% lifetime risk of developing breast cancer. The lifetime risk of dying from prostate cancer is 3.4% for American men. Pop Quiz: What is the lifetime risk of death for the entire population? Answer: 100%.
Ligament:  A tough band of connective tissue that connects various structures such as two bones. From the Latin "ligare" meaning "to bind or tie."
Ligand:  A molecule that binds to another. Often, a soluble molecule such as a hormone or neurotransmitter that binds to a receptor.
Ligate:  To tie or to tie off, as in to ligate an artery.
Ligature:  In surgery, a filament or thread used to tie something, such a blood vessel to prevent it from bleeding or the pedicle of a tumor to constrict it. Ligatures may be of silk, gut, wire, and other materials.
Lightening:  (Not to be confused with a discharge of atmospheric electricity which is spelled lightning), lightening refers to the sensation that a pregnant woman feels when the baby drops. This is the time when the presenting (lowermost) part of the fetus descends into the maternal pelvis. Lightening classically occurs 2 to 3 weeks before labor begins. However, it may not occur in women who have had two or more prior viable pregnancies (i.e. multiparas) until labor actually begins. Lightening is also called "engagement" because the presenting part of the fetus is then engaged in the mother's pelvis.
Lightning injuries:  A major source of injury and death from the environment, lightning is one of the top three causes of death from the environment. The other top environmental killers are floods and extreme temperatures. Lightning is neither a direct current nor an alternating current. It is a unidirectional, massive, current impulse with several return strokes back to the cloud. Once connection from the cloud is made, a tremendously large current flows for an incredibly short time. The most important difference between lightning and high-voltage electrical injuries is the duration of exposure to the current. Lightning has only brief contact with the skin, not enough time to cause skin burns. Internal burns and renal failure play a small part in the injury pattern from lightning. Cardiac and respiratory arrest, vascular spasm, and neurologic damage play a much greater role.
Lilliputian hallucination:  An hallucination in which things, people, or animals seem smaller than they would be in real life. Lilliputian refers to the "little people" who lived (fictionally) on the island of Lilliput in Jonathan Swift's 1726 masterpiece Gulliver's Travels.
Limb-girdle muscular dystrophy:  One of a group of diseases that may begin in childhood or later with slowly progressive weakness and wasting of the muscles restricted to the limb musculature, especially to the hips and shoulders. Muscle biopsies of the limb-girdle muscular dystrophies typically show degeneration and regeneration of muscle. There is usually an elevated CPK (creatine phosphokinase) in the blood. Most patients show relative sparing of the heart and bulbar muscles. The limb-girdle muscular dystrophies are caused a number of genetic defects and can affect both males and females. Inheritance is usually autosomal recessive.
Liminal:  In neurolgy, at the threshold of perception to a sensory stimulus. In other words, just barely perceptible to the senses.
Lindane:  An organochlorine pesticide and nerve poison. Also a suspected carcinogen (cancer-causing agent). Although many countries have banned lindane, it is still used in the US for treating head lice and scabies. Also known as gamma-hexachlorocyclohexane (HCH). The US Food and Drug Administration in 2003 announced stronger warnings and a medication guide to be distributed directly to patients purchasing Lindane Lotion and Lindane Shampoo for the treatment of scabies and lice.
Lingelsheimia:  A group of bacteria named after W. von Lingelsheim. Now known as Acinetobacter.
Lingual:  1. Having to do with the tongue. 2. Next to the tongue. In dentistry, the tooth surface next to the tongue. 3. Toward the tongue. 4. Produced by the tongue as, for example, lingual speech.
Lingual gyrus:  An area in the occipital lobe, the visual processing center in the brain. The lingual gyrus extends to the temporal lobe of the brain. A stroke damaging the lingual gyrus reportedly can cause a loss of dreaming, suggesting that the lingual gyrus plays a key role in generating or recalling dreams. The lingual gyrus is so-named because it resembles the tongue in shape.
Linkage:  The tendency for genes and other genetic markers to be inherited together because of their location near one another on the same chromosome.
Linkage analysis:  Study aimed at establishing linkage between genes. Today linkage analysis serves as a way of gene-hunting and genetic testing.
Linkage map:  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).
Linus Pauling:   (1901-1994) American chemist who won the 1954 Nobel Prize in Chemistry "for his research into the nature of the chemical bond and its application to the elucidation of the structure of complex substances." He also won the 1962 Nobel Peace Prize, making him the only person to win two unshared Nobel prizes.
Lipectomy, suction-assisted:  Another name for liposuction, the surgical removal of fat deposits from specific parts of the body, the most common being the abdomen (the "tummy"), buttocks ("behind"), hips, thighs and knees, chin, upper arms, back, and calves. The technique breaks up and "sucks" fat out of the body through a canula (a hollow instrument) inserted subdermally (under the skin) thanks to a strong high-pressure vacuum that is applied to the cannula.
Lipid:  A substance such as a fat, oil or wax that dissolves in alcohol but not in water. Lipids contain carbon, hydrogen and oxygen but have far less oxygen proportionally than carbohydrates. Lipids are an important part of living cells. Together with carbohydrates and proteins, lipids are the main constituents of plant and animal cells.
Lipid profile:  Pattern of lipids in the blood. (A lipid profile usually includes the total cholesterol, high density lipoprotein (HDL) cholesterol, triglycerides, and the calculated low density lipoprotein (LDL) cholesterol.
Lipodystrophy:  A disorder of adipose (fatty) tissue characterized by a selective loss of body fat. Patients with lipodystrophy have a tendency to develop insulin resistance, diabetes, a high triglyceride level (hypertriglyceridemia), and fatty liver. There are numerous forms of lipodystrophy that are genetic (inherited) or acquired (not inherited).
Lipodystrophy syndrome:  A disturbance of lipid (fat) metabolism that involves the partial or total absence of fat and often the abnormal deposition and distribution of fat in the body. There are a number of different lipodystrophy syndromes. Some of them are present at birth (congenital) while others are acquired later. Some are genetic (inherited), others are not.
Lipodystrophy, cephalothoracic:  A disorder characterized by painless symmetrical diffuse deposits of fat beneath the skin of the neck, upper trunk, arms and legs.
Lipoid nephrosis:  The earliest stage of nephrosis (the nephrotic syndrome of childhood).
Lipoidosis, sphingomyelin:  Also called Niemann-Pick disease, this is a disorder of the metabolism of a lipid (fat) called sphingomyelin that usually causes the progressive development of enlargement of the liver and spleen (hepatosplenomegaly), "swollen glands" (lymphadenopathy), anemia and mental and physical deterioration. Niemann-Pick disease is hereditary and follows an autosomal recessive pattern. The onset of the classical form is in very early infancy and death is usually before age 3. The lipid accumulates in cells (called reticuloendothelial cells) in the liver and spleen and other cell types throughout the body including the nerve ganglion cells of the central nervous system. The neurological features of Niemann-Pick disease include mental retardation, spasticity, seizures, jerks, eye paralysis (ophthalmoplegia) and ataxia (wobbliness). Physical growth is retarded.
Lipoma:  A benign fatty tumor.
Lipomatosis, multiple symmetric:  A disorder characterized by painless symmetrical diffuse deposits of fat beneath the skin of the neck, upper trunk, arms and legs. The condition is thought to be genetic although its exact mode of inheritance is uncertain.
Lipoprotein:  A complex of lipid and protein, the fomr in which lipids travel in the blood. Cholesterol, a building block of the outer layer of cells (cell membranes), is transported through the blood in the form of water- soluble carrier molecules known as lipoproteins. The lipoprotein particle is composed of an outer shell of phospholipid, which renders the particle soluble in water; a core of fats called lipid, including cholesterol and a surface apoprotein molecule that allows tissues to recognize and take up the particle. These lipoproteins are characterized by their density: high density lipoprotein (HDL), low density lipoprotein (LDL), very low density lipoprotein (VLDL).
Liposarcoma:  A malignant tumor that arises in fat cells in deep soft tissue, such as that inside the thigh. Most frequent in middle-aged and older adults (age 40 and above), liposarcomas are the most common of all soft-tissue sarcomas.
Liposuction:  The most common cosmetic operation in the U. S. with over 400,000 such surgical operations done annually, liposuction involves the surgical suctioning of fat deposits from specific parts of the body, the most common being the abdomen , buttocks, hips, thighs and knees, chin, upper arms, back, and calves. Liposuction breaks up and "sucks" fat out of the body. This is done through a canula (a hollow instrument) inserted under the skin. A high-pressure vacuum is applied to the cannula.
Liquid diet:  The Liquid diet is the restriction of solid food intake, and replacement of solid food with liquids. In hospitals, liquid diets are prescribed by doctors for a number of reasons for patients who are unable to consume solid foods. Liquid diets may be prescribed following surgery or as a preparation for certain medical procedures. Additionally, some people have injuries or medical conditions that limit their ability to eat solid foods. Most prescribed liquid diets allow sports drinks, broth, tea, and coffee. Strained juices may also be permitted. In terms of weight loss, various diet plans have been developed that may be termed "liquid diets," since these involve replacing all or part of one's food consumption with liquids. These diets may include specifically formulated diet drinks or may be based upon consumption of teas and juices. Many liquid diets may not be nutritionally sound and safe for long-term weight loss.
Liquid nitrogen:  Nitrogen in a liquid state. Liquid nitrogen is supercool -- about 200 degrees Celsius (320 degrees Fahrenheit) below zero -- and is used for cryopreservation, cryosurgery, and cryomedicine. Liquid nitrogen is invaluable for preserving blood and bone marrow cells, sperm, ova, early embryos, and, in the microbiology laboratory, a variety of microorganisms (bacteria, fungi, etc). In cryosurgery, a super-chilled scalpel may be used to remove cancer tissue. In dermatology, liquid nitrogen is commonly used to freeze benign growths, precancers, and skin cancers. The liquid nitrogen is usually applied by a spray bottle (canister) or a cotton swab. It is the thawing process that damages the cells. Liquid nitrogen is also known as LN2.
Liquor cerebrospinalis:  The latin term for cerebrospinal fluid.
Lisfranc fracture:  A dislocation of the midfoot most commonly caused by stepping into a hole and falling forward or similar forces on the foot. The injury is named for the French doctor who first described this type of injury. The area of the midfoot that is dislocated contains a cluster of small bones that forms an arch on top of the foot between the ankle and the toes. From these bones, the long bones known as metatarsals extend down the foot toward the toes. Lisfranc injuries are often mistakenly diagnosed as sprains and are difficult to identify on X-rays. In some cases, CT or MRI scans can help establish the diagnosis of a Lisfranc fracture. Treatment can involve casting or surgical repair for more severe cases.
Lissencephaly:  A brain malformation characterized by microcephaly and the lack of normal convolutions (folds) in the brain. Lissencephaly literally means "smooth brain." It is caused by defective neuronal migration, a defect in the process in which nerve cells move from their place of origin to their permanent location. The surface of a normal brain is formed by a complex series of folds and grooves. The folds are called gyri or convolutions, and the grooves are called sulci. In children with lissencephaly, the normal convolutions are absent or only partly formed, making the surface of the brain smooth. The prognosis for children with lissencephaly varies depending on the degree of brain malformation. Many individuals show no significant development beyond a 3- to 5-month-old level. Some may have near-normal development and intelligence. Many will die before the age of 2. Respiratory problems are the most common causes of death.
Listeria:  A group of bacteria capable of causing illness (termed listeriosis) including potentially fatal infections in the elderly, newborns, pregnant women, and persons with a weakened immune system. Listeria monocytogenes is the form of Listeria most commonly responsible for infections. Symptoms of listeriosis include fever, muscle aches, nausea and diarrhea. If infection spreads to the nervous system, symptoms such as headache, stiff neck, confusion, loss of balance, or convulsions can occur. Infection during pregnancy may appear mild but can lead to stillbirth, premature delivery and infection of the newborn. Listeria contamination has been responsible for numerous recalls of food.
Liter:  A metric measure of capacity that, by definition, is equal to the volume of a kilogram of water at 4 degrees centigrade and at standard atmospheric pressure of 760 millimeters of mercury. Metric equivalents -- There are 1000 cubic centimeters or 1 cubic decimeter in 1 liter. U.S. equivalent -- A liter is a little more than a quart (1.057 U.S. liquid quarts). The abbreviation for liter is L or l. The word "liter" derives from the French "litre" and that, in turn, is derived from the Latin "litra", a pound.
Lithium:  Lithium carbonate (brand names: Eskalith; Lithobid), a drug used as a mood stabilizer for the treatment of manic/depressive (bipolar) disorder. It prevents or diminishes the intensity of episodes of mania in bipolar patients. Typical symptoms of mania include pressure of speech, motor hyperactivity, reduced need for sleep, flight of ideas, grandiosity, elation, poor judgment, aggressiveness and possibly hostility. Lithium is a positively charged element or particle similar to sodium and potassium and interferes within the cell and on the cell surface with other positively charged atoms such as sodium and potassium. It interferes at several places inside cells and on the cell surface with other positively charged atoms such as sodium, potassium, calcium, and magnesium which are important in many cellular functions.
Lithotomy:  Surgical removal of a stone, especially a kidney or bladder stone.
Lithotomy position:  Position in which the patient is on their back with the hips and knees flexed and the thighs apart. The position is often used for vaginal examinations and childbirth.
Lithotripsy:  A procedure using ultrsound to break a stone into small particles that can be passed in the urine. An "extracorporeal shock wave is delivered from outside the body. There are several methods available for producing an acoustical or ultrasonic "big bang" which can be focused from outside the body onto the kidney and the kidney stone. The stone breaks up after 800 to 2000 shocks. Lithotripsy results are generally good with kidney stones that are less than 1.5 cm (5/8th of an inch) in diameter. The lithotriptor (the stone crushing machine) used to crush kidney stones is operated by a urologist. Anesthesia may be necessary to control the pain.
Lithotripsy, percutaneous nephro- (PNL):  A technique for removing large and/or dense stones and staghorn stones. PNL is done via a port created by puncturing the kidney through the skin. There is no surgical incision. PNL is done under anesthesia and real-time live x-ray control (fluoroscopy). Because x-rays are involved, a sub-specialist in radiology (an interventional radiologist) may perform this part of the procedure. The urologist (an endourologist, another sub-specialist) then inserts instruments via this port into the kidney to break up the stone and remove most of the debris from the stone.
Litmus:  A pigment used as a test for acidity and alkalinity. Litmus paper turns red in acid and blue in an alkaline solution. Litmus is prepared from lichens like Roccella tinctoria.
Livedo reticularis:  A mottled purplish discoloration of the skin. Livedo reticularis can be a normal condition that is simply more obvious when a person is exposed to the cold. Livedo reticularis can also be an indicator of impaired circulation.
Liver:  An organ in the upper abdomen that aids in digestion and removes waste products and worn-out cells from the blood. The liver is the largest solid organ in the body. It is said there is 90% redundancy in the liver, i.e. one can survive with only 10% of the liver functioning. It is also now possible to transplant a liver. Because of redundancy, one can donate a portion ("lobe") of one's liver to another person in what is a life-saving operation.
Liver biopsy:  A procedure in which a small sample of the liver is removed for the diagnosis of abnormal liver conditions. The most common method is percutaneous ("through the skin"). A percutaneous biopsy involves numbing a small area of skin over the lower right side of the chest (directly over the liver). A local anesthetic is injected with a needle. The needle is introduced further with additional injections of anesthetic all the way through the chest wall and into the liver. This numbs the tract that the biopsy needle will take and reduces discomfort. Next a special biopsy needle is inserted into the same area and the biopsy needle is inserted quickly into the liver and withdrawn. Suction through the needle, applied via an attached syringe, causes a small piece of liver (the biopsy) to be pulled into the needle and cut off from the rest of the liver.
Liver cancer, adult primary:   A tumor in which the cancer starts during adulthood in cells in the liver. Also called hepatocellular carcinoma. The signs and symptoms may include a hard lump just below the rib cage on the right side (from swelling of the liver), discomfort in the upper abdomen on the right side, pain around the right shoulder blade, or yellowing of the skin (jaundice). There is often an increase in the blood levels of alpha-fetoprotein (AFP) and alkaline phosphatase. A rapid deterioration of liver function may be the only clue to the presence of the tumor.
Liver cancer, childhood primary:  A cancer that starts in the liver in children, a relatively rare malignancy in children. There are 2 main types of primary liver cancer in children -- hepatoblastoma and hepatocellular carcinoma. Hepatoblastomas usually occur before 3 years of age, whereas the incidence of hepatocellular carcinoma varies little with age between 0 and 19 years. The overall survival rate for children with hepatoblastoma is 70% but is only 25% for hepatocellular carcinoma. Most children with hepatoblastoma or hepatocellular carcinoma have a tumor marker in the blood called alpha-fetoprotein (AFP), that parallels the activity of their disease.
Liver disease:  Liver disease refers to any disorder of the liver.
Liver fluke (Fasciola hepatica):  A parasite which causes Fascioliasis or "liver rot" in ruminants and many other mammals, including people. Eating contaminated vegetation such as watercress is a common mode of infection. Fasciola hepatica is found throughout all regions of the world, both temperate and tropical.
Liver of pregnancy, acute fatty:  Liver failure in late pregnancy, usually from unknown cause. Acute fatty liver of pregnancy (AFLP) typically occurs in first-time pregnancies in the last trimester. AFLP causes nausea and vomiting, abdominal pain especially in the upper abdomen (epigastrium), jaundice (yellowing), frequent thirst (polydipsia) and increased urination (polyuria), fatigue, headache, and altered mental state. Laboratory features of AFLP include profoundly low blood sugar (hypoglycemia), Elevated liver enzymes (e.g., serum transaminase activity) and low levels of platelets (cell fragments in blood needed for clotting). The liver is infiltrated with fat. If untreated, AFLP can cause complete liver failure, bleeding (because of impaired blood clotting) and death of the mother and child. AFLP is treated by delivering the baby as soon as possible. Early diagnosis of AFLP and prompt delivery dramatically improve the outcome and the once-bleak outlook. Women with AFLP generally improve soon after delivery, unless the liver damage is severe. As a general rule, AFLP does not usually recur during a subsequent pregnancy.
Liver pain:  Pain coming from the liver. The liver does not contain nerve fibers that sense pain. Therefore, liver tissue can be cut, burned, or compressed without causing pain. There are pain fibers, however, in the liver's capsule, a thin layer of tissue that surrounds the liver tissue itself. The pain fibers of the capsule are stimulated when the capsule is stretched. Thus anything that stretches the capsule can cause liver pain. The common liver diseases that stretch the capsule are tumors that grow within the liver and inflammation of the liver that occurs, for example, with hepatitis of any cause.
Liver shunt:  Normal blood flow in the abdomen proceeds from the intestines through the portal vein into the liver and then out from the liver through the hepatic vein and on to the heart. A liver shunt is a tube connecting the portal vein and the hepatic vein, thus by[passsing the liver. The technical term for this tube is a Transjugular Intrahepatic Portosystemic Shunt (TIPS). A TIPS is used primarily (but not exclusively) in patients with cirrhosis in which the scar tissue within the liver has blocked the flow of blood from the intestine through the liver via the portal vein. Left untreated this blockage increases the pressure in the portal vein (portal hypertension). As a result of the increase in pressure, blood finds other (small) otherwide unimportant veins around the liver that connect the portal vein with other larger veins within the abdomen. These small veins enlarge and are referred to as varices. Unfortunately, one of the places varices form is in the stomach and lower esophagus, and these varices have a tendency to bleed massively, frequently causing death from exsanguination (bleeding out). By providing an artificial path (shunt) for blood traveling from the intestines - around rather than through the liver - and back to the heart, TIPS reduces the pressure in the varices and prevents them from rupturing and bleeding.
Liver spots:  Pigmented flat spots on sun-exposed skin in older adults, especially on the back of the hands and on the forehead. Liver spots are benign. Medically called a senile lentigo. Despite the name, they have nothing to do with the liver.
Liver transplant:  Surgery to remove a diseased liver and replace it with a healthy liver (or part of one) from a donor. The most common reasons for liver transplantation in children is biliary atresia (a disease in which the ducts that carry bile out of the liver are missing or damaged) while in adults the most common reason for a liver transplant is cirrhosis (a disease in which healthy liver cells are killed and replaced with scar tissue). There is no effective treatment for end-stage liver disease other than a transplant.
Livid:  Black and blue. Also ashen. Also pallid. Also reddish. (Too many meanings cheapen all meanings.)
Living donor liver transplantation:  An option for patients who need a liver transplant. In this procedure, a healthy person (usually a family member, friend or co-worker) donates a portion of their liver to the transplant patient. One of the two lobes of the donor's liver is removed. The recipient's damaged liver is also removed. The healthy liver lobe is then attached in the place from which the recipient's liver was removed. There it begins rapidly to regenerate healthy liver tissue. The donor's liver also quickly regenerates and continues to function normally.
Lizard bite:  Only two types of lizards are poisonous: the Gila monster that lives in Arizona and Mexico and the beaded lizard of Mexico. Symptoms from their bites of these include pain, swelling, and discoloration in the area around the bite and swollen lymph nodes.
Lobar::  Having to do with a lobe. For example, lobar pneumonia.
Lobe:  Part of an organ that appears to be separate in some way from the rest. A lobe may be demarcated from the rest of the organ by a fissure (crack), sulcus (groove), connective tissue or simply by its shape. For example, there are the frontal, parietal, temporal, and occipital lobes of the brain.
Lobectomy::  An operation done to remove a lobe of an organ such as the lobe of a lung or a lobe of the thyroid gland.
Lobstein's disease:  Osteogenesis imperfecta type I. An inherited, generalized connective tissue disorder featuring bone fragility and blue sclerae (blue whites of the eyes). The classic mild form of "brittle bone disease." It is a dominant trait with males and females affected.
Lobule:  A small lobe.
Local seizure:  A seizure that affects only one part of the brain. Symptoms depend on which part is affected.
Local therapy:  Treatment that affects only a tumor and the area close to it.
Lochia:  The fluid that weeps from the vagina for a week or so after delivery of a baby. At first the lochia is primarily blood, followed by a more mucousy fluid containing dried blood, and finally a clear-to-yellow discharge.
Locked-in syndrome:  A neurological disorder characterized by complete paralysis of voluntary muscles in all parts of the body except for those that control eye movement. The locked-in syndrome is usually a complication of a cerebrovascular accident (a stroke) in the base of the pons in the brainstem. The patient is alert and fully conscious but cannot move. Only vertical movements of the eyes and blinking are possible. Locked-in syndrome can also be due to traumatic brain injury, demyelinating diseases (disorders in which the insulating material around brain cells is lost), and medication overdose. There is no cure for locked-in syndrome, nor is there a standard course of treatment. Functional neuromuscular stimulation may help activate some paralyzed muscles. Several devices to help communication are available. Other treatment is symptomatic and supportive. The prognosis for those with locked-in syndrome is poor. The majority of patients do not regain function. There is a temporary form of locked-in syndrome which occurs with anesthesia preceding or during surgery.
Lockjaw:  See tetanus.
Locoregional:  Limited to a local region.
Locoregional anesthesia:  Anesthesia that produces loss of pain only in the region of the surgery. This may be done by a "spinal" in which an anesthetic agent is administered by lumbar injection. Locoregional anesthesia is in contrast to general anesthesia on the one hand and local anesthesia on the other.
Locoregional metastasis:  Spread of a cancer only within the region in which it arose. In contrast to systemic metastasis.
Locus:  In genetics, the place a gene occupies on a chromosome. The plural is loci. (Latin for "place.")
Locus minoris resistentiae:  Latin meaning a place of less resistance. A locus minoris resistentiae offers little resistance to microorganisms. For example, a damaged heart valve acts as a locus minoris resistentiae, a place where any bacteria in the bloodstream tend to settle. The concept of a locus minoris resistentiae is an old one but still a valid, useful way of thinking.
Loeys-Dietz syndrome:  An inherited syndrome characterized by aortic aneurysms and other blood vessel abnormalities in children. The condition is often associated with other birth defects. The aortic aneurysms of Loeys-Dietz syndrome are prone to rupture at a smaller size than garden variety aneurysms.
Loiasis:  The disease caused by the eye worm known as loa loa, a parasite that lives in humans and other primates. People contract the parasite when bitten by infected deer flies. The larvae of the worm enter the bloodstream and later develop into adult worms. Symptoms may not appear for months or years after the bite of the fly.
Loin:  The portion of the lower back from just below the ribs to the pelvis.
Long QT syndrome:  A disorder of the heart's electrical system that predisposes individuals to irregular heartbeats, fainting spells, and sudden death. The irregular heartbeats are typically brought on by stress or vigorous activity. Abbreviated LQTS. LQTS is often symptomatic.
Long-chain-3-hydroxyacyl-CoA dehydrogenase deficiency (LCHAD):   Acute fatty liver of pregnancy (AFLP) has been found to be associated in some cases with an abnormality of fatty-acid metabolism. This abnormality is a deficiency of this enzyme.
Longevity:  Lifespan. Increased longevity means a longer life.
Lordosis:  Inward curvature of the spine giving a posture that reminds one of a duck. The spine is not supposed to be absolutely straight, so some degree of curvature is normal. When the curve exceeds the usual range, it may be due to musculoskeletal disease or simply to poor posture.
Lou Gehrig disease:  Amyotrophic lateral sclerosis (ALS), a classic motor neuron disease. Motor neuron diseases are progressive chronic diseases of the nerves that come from the spinal cord responsible for supplying electrical stimulation to the muscles. This stimulation is necessary for the movement of body parts. In North America ALS is often called "Lou Gehrig's disease" after the stalwart baseball player who died from it. In 14 seasons playing for the New York Yankees, ALS strikes in mid-life, most often in the fifth through seventh decades of life. Men are about one-and-a-half times more likely to have the disease as women. It affects about 20,000 Americans with 5,000 new cases occurring in the United States each year. Death typically ensues within three years of diagnosis, although there are notable exceptions. For example the famous physicist Stephen Hawking has suffered from ALS for over 40 years.
Love pearls:  Street name for alpha-ethyltryptamine, a hallucinogenic street drug.
Low back pain:  Pain in the lower back area that can relate to problems with the lumbar spine, the discs between the vertebrae, the ligaments around the spine and discs, the spinal cord and nerves, muscles of the low back, internal organs of the pelvis and abdomen, or the skin covering the lumbar area. Low back pain is the most common complaint which brings patients to doctors.
Low blood pressure:  Any blood pressure that is below the normal expected for an individual in a given environment. Low blood pressure is also referred to as hypotension.
Low blood sugar:  A low blood level of the sugar glucose. Also called hypoglycemia. Hypoglycemia is only significant when it is associated with symptoms. It has many causes including drugs such as insulin, liver disease, surgical absence of the stomach, pre-diabetes, and rare tumors that release excess insulin.
Lower GI series:  Short for lower gastrointestinal series. A series of x-rays of the rectum, colon and lower section of the small intestine taken after the patient has a barium enema. Barium is a white, chalky substance that coats the organs so they will show up on the x-ray. Also called a barium enema or a barium enema x-ray.
Lower motor neuron:   A nerve cell that goes from the spinal cord to a muscle. The cell body of a lower motor neuron is in the spinal cord and its termination is in a skeletal muscle. The loss of lower motor neurons leads to weakness, twitching of muscle (fasciculation), and loss of muscle mass (muscle atrophy). Abbreviated LMN.
Lower segment Cesarian section (LSCS):  A Cesarian section in which the surgical incision (cut) is made in the lower segment of the uterus.
Lucid dreaming:  The process of being aware that one is dreaming. Some researchers believe that in lucid dreaming, the individual may be able to change the outcome of the dream or control their degree of participation in the imaginary (dream) environment. Lucid dreams have been described as arising from either the sleeping or waking state. A number of ongoing studies are examining brain activity during sleep and dreaming to better characterize the phenomenon of lucid dreaming.
Lues:  Pronounced lou-ease. An old name for syphilis, a sexually transmitted disease (STD) that has been around for centuries and is caused by Treponema pallidum, a microscopic organism called a spirochete, a worm-like spiral-shaped organism.
Luetic:  1. Relating to syphilis, caused by it, or suffering from it. 2. A person with syphilis. From lues, an old name for syphilis.
Lumbar:  Referring to the five lumbar vertebrae, the disks below them, and the corresponding area of the lower back. The lumbar vertebrae and their disks are situated below the thoracic vertebrae and above the sacral vertebrae in the spinal column.
Lumbar puncture:  A procedure in which cerebrospinal fluid is removed from the spinal canal for diagnostic testing or treatment. Abbreviated LP.
Lumbar radiculopathy:  Nerve irritation caused by damage to the discs between the vertebrae. Damage to the disc occurs because of degeneration ("wear and tear") of the outer ring of the disc, traumatic injury, or both. As a result, the central softer portion of the disc can rupture (herniate) through the outer ring of the disc and press against the spinal cord or its nerves as they exit the bony spinal column. This rupture is what causes the commonly recognized pain of "sciatica" that shoots down the leg.
Lumbar spinal stenosis:  A condition whereby either the spinal canal (central stenosis) or vertebral foramen (foraminal stenosis) becomes narrowed, leading to compression of the spinal nerves. Symptoms are pain in the lower back and weakness, numbness, pain, and loss of sensation in the legs. The most common cause of lumbar spinal stenosis is degenerative arthritis (osteoarthritis),
Lumbar strain:  A stretching injury to the ligaments, tendons, and/or muscles of the low back. The stretching incident results in microscopic tears of varying degrees in these tissues. Lumbar strain is one of the most common causes of low back pain. The injury can occur because of overuse, improper use, or trauma. It is classified as "acute" if it has been present for days to weeks. If the strain lasts longer than 3 months, it is referred to as "chronic."
Lumbar vertebrae:  The five vertebrae situated between the thoracic vertebrae and the sacral vertebrae in the spinal column. The lumbar vertebrae are represented by the symbols L1 through L5.
Lumen:  Refers to to the channel within a tube such as a blood vessel or to the cavity within a hollow organ such as the intestine.
Lumpectomy:  The surgical removal of a small tumor, which may be benign or cancerous. In common use, lumpectomy refers especially to removal of a lump from the breast.
Lung cancer:  Cancer of the major organ of respiration - the lung. Lung cancer kills more men and women than any other form of cancer. Since the majority of lung cancer is diagnosed at a relatively late stage, only 10% of all lung cancer patients are ultimately cured. Eight out of 10 lung cancers are due to tobacco smoke. Lung cancers are classified as either small cell or non-small cell cancers.
Lung cancer, familial:  Lung cancer that recurs in families. A specific gene has been identified in some of these people.
Lung cancer, non-small cell:  Cancer of the lung which is not of the small cell carcinoma (oat cell carcinoma) type. The term "non-small cell lung cancer" is generally applied to the various types of bronchogenic carcinomas (those arising from the lining of the bronchi) which include adenocarcinoma, squamous cell carcinoma, and large cell undifferentiated carcinoma.
Lung cancer, small cell:  A type of lung cancer in which the cells are small and round. Also called oat cell lung cancer.
Lung reduction surgery:  A surgical treatment for patients with advanced emphysema in which 20-35% of the emphysematous lung is removed to allow the remaining tissue to expand more fully and restore some of the patient's breathing capacity. Also called lung-volume reduction surgery, or LVRS. When this surgery is successful, there is improvement in lung function, exercise capacity, and the quality of life. However, the surgical mortality rate is appreciable (4 to 15%, according to one study) and it is counter-productive in people with the most severe forms of emphysema.
Lung transplant:  The first lung transplant was performed by the American surgeon James Hardy (1918-2003) in 1964.
Lunula (aka Lunule):  1. The crescent-shaped area at the base of a fingernail or toenail. 2. Any small crescent or moon-shaped area or structure. Lunula is the diminuitive of the Latin luna, the moon.
Lupus:  A chronic inflammatory disease that is caused by autoimmunity. Patients with lupus have in their blood unusual antibodies that are targeted against their own body tissues. Lupus can cause disease of the skin, heart, lungs, kidneys, joints, and nervous system.
Lupus in pregnancy:  Systemic lupus erythematosus (SLE) during pregnancy, a high-risk situation. The high risks are to both the mother and child. Women with SLE can have flares of SLE during pregnancy. There is also a markedly increased risk of a miscarriage (spontaneous abortion).
LUQ:  Anatomical abbreviation for left upper quadrant of the abdomen. For example, the LUQ of the abdomen contains the spleen and stomach.
Luteinizing hormone (LH):  A gonadotropin (a hormone that affects the function of the sex organs) that is released by the pituitary gland in response to luteinizing hormone-releasing hormone (LHRH). Abbrevi'ated LH. In females, LH controls the length and sequence of the female menstrual cycle.
Luteinizing hormone-releasing hormone (LHRH):  A hormone that controls sex hormones in men and women.
Luxation:  Complete dislocation of a joint. A partial dislocation is a subluxation.
LVAD:  Left ventricular assist device.
LVF:  1. Left ventricular failure, failure of the left side of the heart. Also 2. Left ventricular function, the function of the left ventricle.
Lycanthropy:  The delusion that one has become a wolf or the werewolf transformation. The word "lycanthropy" is from the Greek "lykos," meaning "wolf" + "anthropos" meaning "human being."
Lycopene:  A red pigment found predominantly in tomatoes (and also in some other fruits) that gives them their color. Lycopene has antioxidant properties and has been claimed to "promote a healthy heart" and to reduce the risk of cancer. Lycopene has not, however, been proven to contribute to the anticancer properties of tomatoes. In fact, there is evidence that it is not lycopene but something else in tomatoes that is responsible. Numerous other potentially beneficial compounds are present in tomatoes. The lower risk of cancer associated with higher consumption of tomatoes and tomato-based products supports current dietary recommendations to increase fruit and vegetable consumption.
Lyme disease:  An inflammatory disease that is caused by the bacterium Borrelia burgdorferi, which is transmitted to humans by the deer tick. The first sign of Lyme disease is a red, circular, expanding rash, usually radiating from the tick bite, followed by flu-like symptoms. The acute phase (first few weeks) is usually cured with antibiotics. If allowed to progress to a chronic stage, treatment becomes much more difficult.
Lymph:  The almost colorless fluid that travels through the lymphatic system, carrying cells that help fight infection and disease.
Lymph node or Lymph gland:  One of many small, bean-shaped organs located throughout the lymphatic system. The lymph nodes are important in the function of the immune response and also store special cells that can trap cancer cells or bacteria that are traveling through the body.
Lymph node, sentinel:  The first lymph node to receive lymphatic drainage from a tumor. The sentinel node for a given tumor is found by injecting a tracer substance around the tumor. This substance then travels through the lymphatic system to the sentinel node. The tracer substance can then be visualized and the sentinel node identified for biopsy.
Lymphadenitis:  inflamed or infected lymph nodes.
Lymphadenitis, regional:  AKA benign lymphoreticulosis and also as cat scratch disease, a mild flu-like infection, with swollen lymph nodes (lymphadenitis) and mild fever of short duration, due to cat scratches, especially from kittens.
Lymphadenopathy:  Abnormally enlarged lymph nodes. Commonly called swollen glands.
Lymphadenopathy virus:  Another name for the human immunodeficiency virus (HIV).
Lymphangiogram:   An X-ray of the lymphatic system for which a dye is injected to outline the lymphatic vessels and organs.
Lymphangioma:  An abnormal structure that consists of a collection of blood vessels and lymph vessels that are overgrown and clumped together. Depending on its nature, a lymphangioma may grow slowly or quickly. Lymphangiomas can cause problems because of their location.
Lymphangitis:  The red streaking and gland (lymph node) swelling in the area of an injury especially on the extremities. It is usually caused by a bacterial infection with Streptococcus. The bacteria enter the body through a cut, scrape, bite or wound of some sort. The bacteria can get into the lymphatic system, which is part of our immune system. The bacterial infection spreads rapidly in the lymph channels causing the red streaks and lymph nodes (hard swollen "knots" under the skin). If left untreated, the bacteria can spread in the skin around the area, causing cellulitis, and also rapidly spread to the bloodstream, causing sepsis. Before antibiotics people referred to lymphangitis as "blood poisoning" due to the infection rapidly causing severe illness and sometimes death.
Lymphatic:  Pertaining to a small, thin channel that is similar to a blood vessel and that collects and carries tissue fluid (lymph) from the body. This fluid ultimately drains back into the bloodstream. in the chest close to hte heart.
Lymphatic filariasis:  A parasitic disease caused by the African eye worm, a microscopic thread-like worm. The adult worms can only live in the human lymph system.
Lymphatic system:  The tissues and organs, including the bone marrow, spleen, thymus, and lymph nodes, that produce and store cells that fight infection and disease. The channels that carry lymph are also part of this system.
Lymphatic tissue:  A part of the body's immune system that helps protect it from bacteria and other foreign entities. Lymphatic tissue is rich in lymphocytes (and accessory cells such as macrophages and reticular cells). The lymphatic tissue includes the lymph nodes, spleen, tonsils, adenoids and the thymus (an organ in the chest that is particularly large during infancy). Also known as lyphoid tissue.
Lymphatics:  Small thin channels similar to blood vessels that do not carry blood, but collect and carry tissue fluid (lymph) from the body to ultimately drain back into the blood stream in the chest, close to the heart.
Lymphedema::  A condition in which excess fluid collects in tissue and causes swelling. Lymphedema may occur in the arm or leg after lymph vessels or lymph nodes in the underarm or groin are removed. It usually causes painless swelling. It is common after surgery which removes lymph nodes (usually surgery for cancer).
Lymphoblastic leukemia, acute (ALL):  A form of leukemia that has a sudden onset and is characterized by the presence in the blood and bone marrow of large numbers of unusually immature white blood cells destined to become lymphocytes. These cells are called lymphoblasts, Also known as acute lymphocytic leukemia (ALL).
Lymphocytes:  A small white blood cell (leukocyte) that plays a large role in defending the body against disease. Lymphocytes are responsible for immune responses. There are two main types of lymphocytes: B cells and T cells. The B cells make antibodies that attack bacteria and toxins while the T cells attack body cells themselves when they have been taken over by viruses or have become cancerous. Lymphocytes secrete products (lymphokines) that modulate the functional activities of many other types of cells and are often present at sites of chronic inflammation.
Lymphocytic:  Referring to lymphocytes, a type of white blood cell. For example, lymphocytic inflammation in the skin is skin that is infiltrated with 'lymphocytes.
Lymphocytic colitis:  A type of inflammatory disease of the large intestine (colon). The name derives from the microscopic observations of biopsies of the colon. What is seen in the microscope view of colon tissue is an increased number of inflammatory white blood cells (lymphocytes) among the lining cells of the colon. The elderly are most commonly affected by lymphocytic colitis, and symptoms of the condition typically include a chronic, watery diarrhea without the presence of blood. Abdominal pain and cramping may also occur in people with lymphocytic colitis. Since the colon appears normal under colonoscopy, this condition has been referred to as "microscopic colitis" because the characteristic abnormalities are only apparent when biopsies of the colon are examined microscopically.
Lymphocytosis:  Having too many lymphocytes. Lymphocytosis may be a marker that infection or disease is present.
Lymphogranuloma venereum (LGV):  An uncommon genital or anorectal (affecting the anus and/or rectum) infection that is caused by a specific type of Chlamydia trachomatis. Patients with LGV typically have tender lymph nodes in the groin.
Lymphoid:  Referring to lymphocytes, a type of white blood cell, or to tissue in which lymphocytes develop. Lymphoid tissue is full of lymphocytes, such as a lymph node.
Lymphoid tissue:  The part of the body's immune system that is important for the immune response and helps protect it from infection and foreign bodies. Lymphoid tissue is present throughout the body and includes the lymph nodes, spleen, tonsils, adenoids, and other struct. Also known as lymphatic tissue.
Lymphoma:  A tumor of the lymphoid tissue. The major types of lymphoma are Hodgkin's disease and non-Hodgkin's lymphoma (NHL). NHL can in turn be divided into low-grade, intermediate-grade, high-grade, and miscellaneous lymphomas. The course of NHL varies greatly.
Lymphoproliferative:  Referring to the proliferation of the bone marrow cells that give rise to lymphoid cells (such as lymphocytes and plasma cells) and reticuloendothelial cells (such as macrophages, which engulf foreign particles).
Lymphoproliferative disorders:  Malignant diseases of the lymphoid cells and of cells from the reticuloendothelial system that usually occur in people with compromised immune systems, such as patients with AIDS and recent transplant patients.
Lyonization (Lyon Hypothesis):  The inactivation of an X chromosome. One of the two X chromosomes in every cell in a female is randomly inactivated early in embryonic development. Named after geneticist Mary Lyon.
Lyophilization:  A process by which material is rapidly frozen and dehydrated under high vacuum.
Lyophilize:  To freeze-dry. The material is rapidly frozen and dehydrated under high vacuum.
Lysergic acid diethylamide:  Better known as LSD. (LSD is the abbreviation for the German name for the drug: Lysergsaure-Diathylamid.)
Lysine:  An amino acid, one of the 20 building blocks of protein. A dietary essential amino acid, lysine is present in many proteins and is necessary for optimal growth in childhood. Helps to suppress herpes virus. Symbol: Lys
Lysis:  Destruction. For example, hemolysis is the destruction of red blood cells with the release of hemoglobin; bacteriolysis is the destruction of bacteria; etc. Lysis can also refer to the subsidence of one or more symptoms of an acute disease as, for example, the lysis of fever in pneumonia.
Lysosomal enzyme:  An enzyme in an organelle (a "cell" within a cell) called the lysosom within the cell. Lysosomal enzymes break down large molecules and other materials (such as bacteria) that have been taken up by the cell during the process of endocytosis. In endocytosis, large molecules and particles from outside the cell are taken up by the cell via a progressive invagination (inpouching) and eventual pinching off of a region of the cell membrane, forming a membrane-bound vesicle (bubble) within the cytoplasm of the cell. The vesicle then fuses with the lysosome and the lysosomal enzymes destroy the foreign material by hydrolysis. The lysosomal enzymes do not normally damage the cell itself.

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