Dictionary

melena Stool or vomit that is stained black by blood pigment or dark blood products.

melorheostosis A rare bone condition that usually begins in childhood and is characterized by thickening of the bones (sclerosis) of a limb. Pain is frequent in the involved limb, and the affected bone can have the appearance of dripping candle wax on an X-ray.

membrane A very thin layer of tissue that covers a surface.

membrane attack complex An abnormal activation of the complement (protein) portion of the blood that forms a cascade reaction and brings blood proteins together, binds them to the cell wall, and then inserts them through the cell membrane. Abbreviated MAC. MAC allows water, ions, and other small molecules to move freely into and out of…

membranous glomerulonephritis A disease affecting the glomerulus, the tiny structure in the kidney composed of capillary blood vessels that is actively involved in the filtration of the blood to form urine. The main sign of the disease is marked proteinuria. The majority of cases are primary, meaning the cause is not known. The remaining cases…

memory The ability to recollect information about past events or knowledge, and/or the process of doing so. Memory is often divided into short-term (also known as working, or recent, memory) and long-term memory: Short-term memory recovers memories of recent events, and long-term memory is concerned with the more distant past. Some medical disorders, such as…

memory, anterograde Memory for things following an event or brain injury. The opposite of retrograde memory.

memory, long-term The ability to permanently store, manage, and retrieve information for later use. Items of information stored as long-term memory may be available for a lifetime.

MEDLARS Medical Literature Analysis and Retrieval System, a computer system of the US National Library of Medicine (NLM) that allows rapid access to NLM’s store of biomedical information. MEDLARS search services are available around the world without charge. See also MEDLINE.

MEDLINE The best-known bibliographic database of the US National Library of Medicine (NLM), which lets anyone with computer access query the NLM’s store of journal references on specific topics. The MEDLINE database covers the fields of medicine, nursing, dentistry, veterinary medicine, the health care system, and the preclinical sciences. MEDLINE is part of the MEDLARS…

medulla The innermost part. For example, the adrenal medulla is the innermost part of the adrenal gland, the renal medulla is the inner part of the kidney, and the spinal medulla is the part of the spinal cord that is lodged deep within the vertebral canal.

medulla, adrenal The innermost portion of the adrenal gland, which makes epinephrine (adrenaline) and norepinephrine (noradrenaline). These hormones cause the breakdown of the storage product glycogen to the sugar glucose in the liver, facilitate the release of fatty acids from adipose (fat) tissue, cause narrowing (constriction) of most blood vessels in the body, and increase…