| countercurrent exchanger | A system in which heat or chemicals passively diffuse across a membrane separating two countercurrent exchanger streams so that at each end the fluid leaving along one side of the membrane nearly resembles, in temperature or composition, the fluid entering the other; e.g., the venae comites in the arms serve as a countercurrent exchanger exchanger, the arterial blood serving to rewarm the cooler venous blood. (05 Mar 2000) |
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| anion exchanger | Family of Integral membrane proteins that perform the exchange of chloride and bicarbonate across the plasma membrane. Best known is Band III protein of the red blood cell. (18 Nov 1997) |
| cation exchanger | An insoluble solid (usually a polystyrene or a polysaccharide) that has negatively charged radicals attached to it (e.g., -COO-, -SO3-), which can attract and hold cations that pass by in a moving solution if these are more attracted to the acid groups than the counter ion present. (05 Mar 2000) |
| countercurrent | 1. Flowing in an opposite direction. 2. A current flowing in a direction opposite to another current. (05 Mar 2000) |
| countercurrent distribution | A method of separation of two or more substances by repeated distribution between two immiscible liquid phases that move past each other in opposite directions. It is a form of liquid-liquid chromatography. (12 Dec 1998) |
| countercurrent mechanism | A system in the renal medulla that facilitates concentration of the urine as it passes through the renal tubules. See: countercurrent exchanger, countercurrent multiplier. (05 Mar 2000) |
| countercurrent multiplier | A system in which energy is used to transport material across a membrane separating two countercurrent multiplier tubes connected at one end to form a hairpin shape; by this means a concentration can be achieved in the fluid in the hairpin bend, relative to the inflow and outflow fluids, that is much greater than the transport mechanism could produce between the two sides of the membrane at any point; e.g., the nephronic loops in the renal medulla act as countercurrent multipliers. (05 Mar 2000) |
| sodium-calcium exchanger | An electrogenic ion exchange protein that maintains a steady level of calcium by removing an amount of calcium equal to that which enters the cells. It is widely distributed in most excitable membranes, including the brain and heart. (12 Dec 1998) |
| ion exchanger | See: anion exchanger, cation exchanger. (05 Mar 2000) |
| absolute system of units | A system based on absolute units accepted as being fundamental (length, mass, time) and from which other units (force, energy or work, power) are derived; such system's in common use are the foot-pound-second, centimeter-gram-second, and meter-kilogram-second system's. (05 Mar 2000) |
| absorbent system | <anatomy> The tissues and organs (including the bone marrow, spleen, thymus and lymph nodes) that produce and store cells that fight infection and the network of vessels that carry lymph. (12 May 1997) |
| alimentary system | The organs that are responsible for getting food into and out of the body and for making use of food to keep the body healthy. These include the mouth, oesophagus, stomach, liver, gallbladder, pancreas, small intestine, colon, and rectum. (12 Dec 1998) |
| anterolateral system | A composite bundle of fibres, located in the ventrolateral part of the lateral funiculus, containing spinothalamic, spinohypothalamic, spinoreticular, and spinomesencephalic (spinotectal, spinal to periaqueductal grey, etc.) fibres; occupies the combined areas of the spinal white matter historically divided into anterior and lateral spinothalamic tracts; located in white matter ventral to the denticulate ligament, hence the anatomical basis for the anterolateral cordotomy; concerned with the transmission of nociceptive and thermal information and with crude (nondiscriminative) touch. (05 Mar 2000) |
| anti-allergic and respiratory system agents | A collective term for drugs used to treat allergic reactions as well as those drugs that produce an effect on the respiratory system. (12 Dec 1998) |
| arch-loop-whorl system | See: Galton's system of classification of fingerprints. (05 Mar 2000) |