| isotope clearance | The rate at which an isotope is removed (usually by blood flow) from a tissue or organ such as the brain. (05 Mar 2000) |
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| occlusal clearance | A condition in which the opposing occlusal surfaces may glide over one another without any interfering projection. (05 Mar 2000) |
| osmolal clearance | The volume of urine that would be excreted per minute if the urinary solutes were accompanied by just enough water to make the urine isosmotic with plasma, i.e., so that the solute excretion did not change the osmolality of body fluids. To calculate it, the volume of urine excreted per minute is multiplied by the urinary osmolality (usually measured by freezing point depression) and divided by the plasma osmolality. Osmolal clearance is less than actual urine flow when urine is hyposmotic and exceeds it when urine is hyperosmotic. (05 Mar 2000) |
| endogenous creatinine clearance | A term distinguishing measurements based on the creatinine normally present in plasma; since no infusion is necessary, an average value may be obtained by collecting urine for a long period, e.g., 24 hours. (05 Mar 2000) |
| exogenous creatinine clearance | A term distinguishing measurements based on infusing creatinine intravenously to raise its plasma concentration and facilitate its accurate chemical determination. (05 Mar 2000) |
| urea clearance | The volume of plasma (or blood) that would be completely cleared of urea by one minute's excretion of urine; originally calculated as urine flow multiplied by urine urea concentration divided by concentration of urea in whole blood rather than plasma, representing blood urea clearance rather than plasma urea clearance. (05 Mar 2000) |
| urea clearance test | A test of renal function based on urea clearance. (05 Mar 2000) |
| free water clearance | The amount of water excreted in the urine beyond that which would accompany the excreted solutes if the urine were isosmotic with plasma; it represents the loss of body water in excess of solute tending to raise body osmolality and making urine hyposmotic. Unlike other clearance's, it is calculated by subtracting the osmolal clearance from the actual volume of urine excreted per minute. A negative value for free water clearance represents the amount of water that the body has reclaimed from isosmotic tubule fluid to make the urine hyperosmotic and to lower body osmolality. (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) |
| 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) |