| vitelline membrane | <cell biology> The plasma membrane of the egg. (12 Dec 1998) |
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| vitreous membrane | A condensation of fine collagen fibres in places in the cortex of the vitreous body; formerly thought to form a membrane or capsule at its periphery. Synonym: lamina basalis choroideae. See: posterior limiting layer of cornea (05 Mar 2000) |
| medullary membrane | <anatomy> The layer of vascular connective tissue lining the medullary cavities of bone. Origin: NL, fr. Gr. + a bone. Source: Websters Dictionary (01 Mar 1998) |
| reticular membrane | The membrane formed by cuticular plates of the cells of the spiral organ of Corti; it appears netlike when viewed from above. Synonym: membrana reticularis. (05 Mar 2000) |
| membrane | A thin layer of tissue which covers a surface, lines a cavity or divides a space or organ. (18 Nov 1997) |
| membrane attack complex | <immunology> A term originally used to refer to the heat labile factor in serum that causes immune cytolysis, the lysis of antibody coated cells and now referring to the entire functionally related system comprising at least 20 distinct serum proteins that is the effector not only of immune cytolysis but also of other biologic functions. Complement activation occurs by two different sequences, the classic and alternative pathways. The proteins of the classic pathway are termed components of complement and are designated by the symbols C1 through C9. C1 is a calcium dependent complex of three distinct proteins C1q, C1r and C1s. The proteins of the alternative pathway (collectively referred to as the properdin system) and complement regulatory proteins are known by semisystematic or trivial names. Fragments resulting from proteolytic cleavage of complement proteins are designated with lower case letter suffixes, for example, C3a. Inactivated fragments may be designated with the suffix i, for example C3bi. Activated components or complexes with biological activity are designated by a bar over the symbol for example C1 or C4b, 2a. The classic pathway is activated by the binding of C1 to classic pathway activators, primarily antigen-antibody complexes containing IgM, IgG1, IgG3, C1q binds to a single IgM molecule or two adjacent IgG molecules. The alternative pathway can be activated by IgA immune complexes and also by nonimmunologic materials including bacterial endotoxins, microbial polysaccharides and cell walls. Activation of the classic pathway triggers an enzymatic cascade involving C1, C4, C2 and C3, activation of the alternative pathway triggers a cascade involving C3 and factors B, D and P. Both result in the cleavage of C5 and the formation of the membrane attack complex. Complement activation also results in the formation of many biologically active complement fragments that act as anaphylatoxins, opsonins or chemotactic factors. (05 Jan 1998) |
| membrane bone | A bone that develops embryologically within a membrane of vascularised primitive mesenchymal tissue without prior formation of cartilage. (05 Mar 2000) |
| membrane-bound proton-translocating PPi synthase | <enzyme> From rhodospirillum rubrum; functions as an alternative coupling factor; n,n'-dicyclohexylcarbodiimide-sensitive; catalyses the phosphorylation of pi to ppi, the hydrolysis of ppi and the concomitant translocation of proton across the plasma membrane Registry number: EC 3.6.1.- Synonym: h(+)-ppi synthase (26 Jun 1999) |
| membrane capacitance | The electrical capacitance of a membrane. Plasma membranes are excellent insulators and dielectrics: capacitance is the measure of the quantity of charge that must be moved across unit area of the membrane to produce unit change in membrane potential and is measured in Farads. most plasma membranes have a capacitance around 1 microfarad cmexp 2. (18 Nov 1997) |
| membrane-coating granule | A membrane-bound granule, 100 to 500 nm in diameter, located in the upper layers of the stratum spinosum of certain stratified squamous epithelia. Synonym: lamellar granule, membrane-coating granule, Odland body. (05 Mar 2000) |
| membrane depolarisation | The process or act of neutralising polarity, depriving of polarity, or the result of such action; reduction to an unpolarised condition. <physiology> The reversal of the resting potential in excitable cell membranes when stimulated i.e., the tendency of the cell membrane potential to become positive with respect to the potential outside the cell. A positive shift in a cells resting potential (that is normally negative), thus making it numerically smaller and less polarized, for example 90mV to 50mV. <optics> Depolarisation of light, a change in the plane of polarization of rays, especially by a crystalline medium, such that the light which had been extinguished by the analyser reappears as if the polarization had been anulled. The word is inappropriate, as the ray does not return to the unpolarised condition. Origin: Cf. F. Depolarisation. (27 Oct 1998) |
| membrane dipeptidase | <enzyme> Renal dipeptidase which metabolises thienamycin and related carbapenem antibiotic Registry number: EC 3.4.13.19 Synonym: dehydropeptidase-i, dehydropeptidase I, microsomal dipeptidase (26 Jun 1999) |
| membrane enzyme | <enzyme> An enzyme present or embedded in a biomembrane. (05 Mar 2000) |
| membrane expansion theory | That adsorption of anaesthetics into membranes so alters membrane volume and/or configuration that membrane function is affected in such a way as to produce anaesthesia. (05 Mar 2000) |
| membrane fluidity | Biological membranes are viscous 2 dimensional fluids within their physiological temperature range. (18 Nov 1997) |