| RI | radiation intensity; radioactive isotope; radioimmunology; recession index; recombinant inbred [stra... |
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| RIHSA | radioactive iodinated human serum albumin |
| RISA | radioactive iodinated serum albumin; radioimmunosorbent assay |
| RIU | radioactive iodine uptake |
| MIS | Meiosis-Inducing Substance |
| blood group substance | Blood group-specific substances A and B, solution of complexes of polysaccharides and amino acids that reduces the titre of anti-A and anti-B isoagglutinins in serum from group O persons; used to render group O blood reasonably safe for transfusion into persons of group A, B, or AB, but does not affect any incompatibility that results from various other factors, such as Rh. (05 Mar 2000) |
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| vasodepressor substance | An incompletely characterised chemical, apparently produced during liver damage, that tends to decrease vascular pressures and relax arterial walls. (05 Mar 2000) |
| gelatinous substance | The apical part of the posterior horn (dorsal horn; posterior gray column) of the spinal cord's gray matter, composed largely of very small nerve cells; its gelatinous appearance is due to its very low content of myelinated nerve fibres. Synonym: substantia gelatinosa, Rolando's gelatinous substance, Rolando's substance. (05 Mar 2000) |
| glandular substance of prostate | The glandular tissue of the prostate as distinct from the stroma and capsule. Synonym: substantia glandularis prostatae. (05 Mar 2000) |
| Reichstein's substance | One of several steroids; e.g., Reichstein's substance F (cortisone), Reichstein's substance H (corticosterone), Reichstein's substance M (cortisol), Reichstein's substance Q (cortexone), and Reichstein's substance S (cortexolone). Synonym: Reichstein's compound. (05 Mar 2000) |
| released substance | <haematology> A polysaccharide precursor molecule which is used to make the antigens on the surface of human blood cells that are classified in the ABO blood group system. (09 Oct 1997) |
| central and lateral intermediate substance | The central gray matter of the spinal cord surrounding the central canal. Synonym: substantia intermedia centralis et lateralis, anterior gray column, Stilling's gelatinous substance, substantia gelatinosa centralis. (05 Mar 2000) |
| central gray substance | In general: the predominantly small-celled gray matter adjoining or surrounding the central canal of the spinal cord and the third and fourth ventricles of the brainstem, in particular: the thick sleeve of gray matter surrounding the cerebral sylvian aqueduct in the midbrain, rostrally continuous with the posterior nucleus of the hypothalamus; in sections stained for myelin it stands out from the adjoining tectum and tegmentum by the poverty of its myelinated fibres. Synonym: substantia grisea centralis. (05 Mar 2000) |
| medullary substance | The lipid material present in the myelin sheath of nerve fibres. Synonym: Schwann's white substance. (05 Mar 2000) |
| reticular substance | A filamentous plasmatic material, beaded with granules, demonstrable by means of vital staining in the immature red blood cells. Synonym: alpha substance, filar mass, filar substance, substantia reticularis, substantia reticulofilamentosa. Synonym: reticular formation. (05 Mar 2000) |
| gray substance | The cortex of the brain which contains nerve cell bodies. The gray matter is in contrast to the white matter, the part of the brain that contains myelinated nerve fibres. The gray matter is so named because it in fact appears gray. The white matter is white because that is the colour of myelin, the insulation covering the nerve fibres. In the mysterious affair at styles (1920), agatha christie first quoted the fictional belgian detective hercule poirot in regard to his gray matter: 'this affair must be unravelled from within.' he tapped his forehead. 'these little grey cells. It is up to them as you say over here.' (12 Dec 1998) |
| ground substance | The amorphous material in which structural elements occur; in connective tissue, it is composed of proteoglycans, plasma constituents, metabolites, water, and ions present between cells and fibres. Synonym: substantia fundamentalis. (05 Mar 2000) |
| growth substance | <biology, cell biology> Signal molecules that are involved in the control of cell growth and differentiation. (12 Dec 1998) |
| Rolando's gelatinous substance | The apical part of the posterior horn (dorsal horn; posterior gray column) of the spinal cord's gray matter, composed largely of very small nerve cells; its gelatinous appearance is due to its very low content of myelinated nerve fibres. Synonym: substantia gelatinosa, Rolando's gelatinous substance, Rolando's substance. (05 Mar 2000) |
| chromidial substance | Endoplasmic reticulum in which ribosomal granules are applied to the cytoplasmic surface of the cisternae; involved in the synthesis and secretion of protein via membrane-bound vesicles to the extracellular space. Synonym: chromidial substance, ergastoplasm, rough-surfaced endoplasmic reticulum. (05 Mar 2000) |