| reticular activating system | <physiology> A physiological term denoting that part of the brainstem reticular formation that plays a central role in the organism's bodily and behavorial alertness. It extends as a diffusely organised neural apparatus through the central region of the brainstem into the subthalamus and the intralaminar nuclei of the thalamus; by its ascending connections it affects the function of the cerebral cortex in the sense of behavioural responsiveness; its descending (reticulospinal) connections transmit its activating influence upon bodily posture and reflex mechanisms (e.g., muscle tonus), in part by way of the gamma motor neurons. See: reticular formation. Synonym: non-specific system. (05 Mar 2000) |
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| reticuloendothelial system | The phagocytic system of the body, including the fixed macrophages of tissues, liver and spleen. Rather old fashioned term that is coming back into use, mononuclear phagocyte system is probably better when only phagocytes are meant. (18 Nov 1997) |
| cerebrospinal system | The combined central nervous system and peripheral nervous system. (05 Mar 2000) |
| charge transfer system | A complex between two organic molecules in which an electron from one (the donor) is transferred to the other (the acceptor), becoming generally distributed throughout the latter; subsequent transfer of a hydrogen atom completes the reduction of the acceptor; such complex's are generally highly coloured and may be so observed, a network of hydrogen bridges at the catalytic centre of certain proteases. Synonym: charge transfer system. (05 Mar 2000) |
| rh-hr blood-group system | Erythrocyte isoantigens of the rh (rhesus) blood group system, the most complex of all human blood groups, because the genes differ by determining a different number of the over thirty antigens thus far described and do so with remarkably different quality. The major antigen rh or d is the most common cause of erythroblastosis foetalis. (12 Dec 1998) |
| periodic system | The arrangement of the chemical elements in a definite order as indicated by their respective atomic numbers in such a way that groups of elements with similar chemical properties (similar valence shell electron number) are grouped together. See: Mendeleeff's law. (05 Mar 2000) |
| meter-kilogram-second system | An absolute system based on the meter, kilogram, and second; the basis of the International System of Units. (05 Mar 2000) |
| cholinergic system | <physiology> The system of nerve cells that uses acetylcholine as its neurotransmitter, nerve cells in the cholinergic system are damaged in the brains of Alzheimer patients. (15 Jan 1998) |
| metric system | A system of weights and measures, universal for scientific use, based upon the meter, which was originally intended to be one ten-millionth of a quadrant of the earth's meridian and now is based on the length that light travels in a vacuum in a given period of time (see meter). Prefixes of the meter (and other standards) reflect either fractions or multiples of the meter and are identical to the International System of Units (see International System of Units). The unit of weight is the gram, which is the weight of one cubic centimeter of water, equivalent to 15.432358 grains. The unit of volume is the liter or one cubic decimeter, equal to 1.056688 U.S. Liquid quarts; a cubic centimeter is about 16.23073 U.S. Minims. (05 Mar 2000) |
| chromaffin system | The cells of the body which stain with chromium salts. They occur along the sympathetic nerves, in the adrenal gland, and in various other organs. (12 Dec 1998) |
| rootlet system | <plant biology> Microtubules associated with the base of the flagellum in ciliates and flagellates. Also associated with this region is the rhizoplast. (18 Nov 1997) |
| circulatory system | The circulatory system is a composed of the heart, arteries, capillaries and veins. It serves to transport blood low in oxygen from the body to the lungs and heart (veins) and oxygenated blood from the lungs and heart throughout the body (arteries). (see heart, blood). (12 Dec 1998) |
| phosphoenolpyruvate sugar phosphotransferase system | <enzyme> The bacterial sugar phosphotransferase system (pts) that catalyses the transfer of the phosphoryl group from phosphoenolpyruvate to its sugar substrates (the pts sugars) concomitant with the translocation of these sugars across the bacterial membrane. The phosphorylation of a given sugar requires four proteins, two general proteins, enzyme I and hpr and a pair of sugar-specific proteins designated as the enzyme II complex. The pts has also been implicated in the induction of synthesis of some catabolic enzyme systems required for the utilization of sugars that are not substrates of the pts as well as the regulation of the activity of adenylate cyclase. Registry number: EC 2.7.1.- (12 Dec 1998) |
| closed system | <biology, ecology> A chemical or biological system that exchanges no matter or energy with the ouside environment. (12 Mar 1998) |
| mnss blood-group system | A system of universal human blood group isoantigens with many associated subgroups. The m and n traits are codominant and the s and s traits are probably very closely linked alleles, including the u antigen. This system is most frequently used in paternity studies. (12 Dec 1998) |