| C2a | activated second component of complement |
|---|---|
| C3 | third cervical nerve; third cervical vertebra; third component of complement |
| C3a | activated third component of complement |
| C4 | fourth cervical nerve; fourth cervical vertebra; fourth component of complement |
| C4a | activated fourth component of complement |
| complement system | A group of more than 20 serum proteins, some of which can be serially activated and participate in a cascade resulting in cell lysis. (05 Mar 2000) |
|---|---|
| complement unit | The smallest amount (highest dilution) of complement that will cause haemolysis of a unit of red blood cells in the presence of a haemolysin unit. Synonym: alexin unit. (05 Mar 2000) |
| component of complement | Any one of the nine distinct protein units (designated C1 through C9 and distributed in the a, b, and g electrophoretic partitions of normal serum) that effect the immunological activities long associated with complement. C1 is a complex of three subunits: C1q, C1r, and C1s. C1q (overbar indicates "active form") activates proenzyme C1r to C1r which activates C1s to C1s (also known as C1 esterase), which converts proenzyme C2 to C2b and produces C4b from C4. C2b combines with C4b to form "classical-complement-pathway C3/C5 convertase" (also known as C3 convertase, C5 convertase, and C42). This enzyme cleaves C3 to C3a and C3b, and C5 to yield C5a and C5b, as does "alternative-complement-pathway C3/C5 convertase" (also known as proenzyme factor B, properdin factor B, C3 proactivator, and heat-labile factor). Complement factor I (also known as C3b or C3b/C4b inactivator) inactivates C3b and C4b by a different proteolytic cleavage. Several autosomal recessive disorders have been identified in which one or more of the complement components have been deficient or completely absent. (05 Mar 2000) |
| heparin complement | The protein component of heparin in blood. (05 Mar 2000) |
| thyrotoxic complement-fixation factor | A form of thyrotoxin; an antigen found most readily in thyroid tissue from thyrotoxic individuals; known to be chemically and immunologically distinct from thyroglobulin, and fixes complement when combined with antibody related to the gamma-globulin fraction of serum. With the exception of extremely small concentrations, the antigen is rarely found in normal glands or in diseased glands that are not associated with thyrotoxicosis; it is probably an intracellular substance (possibly a constituent of the "microsomal fraction"), and does not contain iodine in significant quantity. Not related to the complement-fixation reaction occurring with serum in Hashimoto's disease, in which the antigen is thyroglobulin. (05 Mar 2000) |
| adrenergic receptors | Reactive components of effector tissues, most of which are innervated by adrenergic postganglionic fibres of the sympathetic nervous system. Such receptor's can be activated by norepinephrine and/or epinephrine and by various adrenergic drugs; receptor activation results in a change in effector tissue function, such as contraction of arteriolar muscles or relaxation of bronchial muscles; adrenergic receptor's are divided into alpha-receptor's and beta-receptor's, on the basis of their response to various adrenergic activating and blocking agents. Synonym: adrenoceptor, adrenoreceptors. (05 Mar 2000) |
| alpha-adrenergic receptors | Adrenergic receptor's in effector tissues capable of selective activation and blockade by drugs; conceptually derived from the ability of certain agents, such as phenoxybenzamine, to block only some adrenergic receptor's and of other agents, such as methoxamine, to activate only the same adrenergic receptor's. Such receptor's are designated as alpha-receptors. Their activation results in physiological responses such as increased peripheral vascular resistance, mydriasis, and contraction of pilomotor muscles. (05 Mar 2000) |
| ANP clearance receptors | Cell surface proteins that bind atrial natriuretic peptide and ANP fragments without initiating biological action. (05 Mar 2000) |
| ANP receptors | Cell surface receptors for atrial natriuretic peptide that have a single transmembrane spanning element; these have integral kinase and guanylate cyclase domains. (05 Mar 2000) |
| B-cell antigen receptors | In the primary immune response immunoglobulin D and monomeric immunoglobulin M are the B-cell antigen receptors. On memory B-cells, other immunoglobulin molecules can serve as antigen receptors. (05 Mar 2000) |
| beta-adrenergic receptors | Adrenergic receptor's in effector tissues capable of selective activation and blockade by drugs; conceptually derived from the ability of certain agents, such as propranolol, to block only some adrenergic receptor's and of other agents, such as isoproterenol, to activate only the same adrenergic receptor's. Such receptor's are designated as beta-receptors. Their activation results in physiological responses such as increases in cardiac rate and force of contraction (b1), and relaxation of bronchial and vascular smooth muscle (b2). (05 Mar 2000) |
| mannose-6-phosphate receptors | Receptors in Golgi apparatus to which newly synthesised proteins that are destined to enter lysosomes bind. (05 Mar 2000) |
| receptors, adrenergic | Cell-surface proteins that bind epinephrine and/or norepinephrine with high affinity and trigger intracellular changes. The two major classes of adrenergic receptors, alpha and beta, were originally discriminated based on their cellular actions but now are distinguished by their relative affinity for characteristic synthetic ligands. Adrenergic receptors may also be classified according to the subtypes of g-proteins with which they bind; this scheme does not respect the alpha-beta distinction. (12 Dec 1998) |
| receptors, adrenergic, alpha | One of the two major pharmacological subdivisions of adrenergic receptors. The alpha-beta distinction was originally based on cellular effects of receptor activation but now relies on the relative affinities for certain synthetic ligands. Alpha-adrenergic receptors are further subdivided into several subclasses based on studies of endogenous and cloned receptors. (12 Dec 1998) |
| receptors, adrenergic, alpha-1 | A subclass of alpha-adrenergic receptors (receptors, adrenergic, alpha). Alpha-1 adrenergic receptors can be pharmacologically discriminated, e.g., by their high affinity for the agonist phenylephrine and the antagonist prazosin. They are widespread, with clinically important concentrations in the liver, the heart, vascular, intestinal, and genitourinary smooth muscle, and the central and peripheral nervous systems. (12 Dec 1998) |