| paroral membrane | <biology> In ciliates the cilia in the region of the mouth may be fused into a paroral membrane. (18 Nov 1997) |
|---|---|
| vestibular membrane | The membrane separating the cochlear duct from the vestibular canal; it consists of squamous epithelial cells with microvilli toward the ductus, a basement membrane, and a thin layer of connective tissue toward the scala. Synonym: membrana vestibularis, paries vestibularis ductus cochlearis, Reissner's membrane, vestibular wall of cochlear duct. (05 Mar 2000) |
| glassy membrane | The basement membrane present between the stratum granulosum and the theca interna of a vesicular ovarian follicle; it becomes very prominent in large atretic follicles, the basement membrane and associated connective tissue of the hair follicle. Synonym: hyaline membrane. (05 Mar 2000) |
| virginal membrane | An obsolete term for hymen. (05 Mar 2000) |
| glial limiting membrane | A dense, resilient membrane forming the true capsule of the brain and spinal cord, composed of the processes of astrocytes (macroglia cells) and covered throughout by the pia mater, which firmly adheres to it; the two membranes are collectively called the pial-glial membrane. Synonym: membrana limitans gliae. (05 Mar 2000) |
| reissner's membrane | <anatomy> The thin membrane which separates the canal of the cochlea from the vestibular scala in the internal ear. Origin: Named from E. Reissner, A German anatomist. Source: Websters Dictionary (01 Mar 1998) |
| Payr's membrane | A fold of peritoneum that crosses over the left flexure of the colon. (05 Mar 2000) |
| cell membrane | <cell biology> The structure enveloping a cell, enclosing the cytoplasm and forming a selective permeability barrier. It consists of lipids, proteins and some carbohydrates, the lipids thought to form a bilayer in which integral proteins are embedded to varying degrees. Synonym: plasma membrane. (26 Mar 1998) |
| cell membrane permeability | A quality of cell membranes which permits the passage of solvents and solutes into and out of cells. (12 Dec 1998) |
| vitelline membrane | <cell biology> The plasma membrane of the egg. (12 Dec 1998) |
| 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) |