| primary refractory anaemia | Any of a group of anaemic conditions in which there is persistent, frequently advanced anaemia that is not successfully treated by any means except blood transfusions, and that is not associated with another primary disease. (05 Mar 2000) |
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| secondary refractory anaemia | Any persistent anaemia that is successfully treated only by blood transfusions, and that is associated with another condition. (05 Mar 2000) |
| effective refractory period | The period during which impulses may appear but are too weak to be conducted; the longest interval between adequate stimuli, falling just short of the time necessary to allow a propagated response to be evoked in a tissue by the second stimulus; it differs from the functional refractory period in that it is a measure of stimulus interval rather than response interval of time. (05 Mar 2000) |
| total refractory period | The absolute refractory period plus the relative refractory period. (05 Mar 2000) |
| functional refractory period | The minimum interval possible between successive responses to stimulation of a tissue. (05 Mar 2000) |
| blood relative | A relative of a person sharing some of the sources from which genes are derived. These will include many of the genes that operate in the blood and its constituents but no special importance attaches to the blood as a vehicle of inheritance. Spouses are not ordinarily blood relatives and when they are, the marriage is consanguineous and carries a higher risk than average of progeny homozygous by descent from ancestors in common. Such marriages are discouraged and within certain degrees of kindred may be illegal. Origin: a folk metaphor of breeding (05 Mar 2000) |
| relative | One who, or that which, relates to, or is considered in its relation to, something else; a relative object or term; one of two object or term; one of two objects directly connected by any relation. Specifically: A person connected by blood or affinity; strictly, one allied by blood; a relation; a kinsman or kinswoman. "Confining our care . . . To ourselves and relatives." . A relative prnoun; a word which relates to, or represents, another word or phrase, called its antecedent; as, the relatives " who", "which", "that". Source: Websters Dictionary (01 Mar 1998) |
| relative accommodation | Quantity of accommodation required for single binocular vision for any specified distance, or for any particular degree of convergence. (05 Mar 2000) |
| relative afferent pupillary defect | An asymmetry of the pupillomotor input between the two eyes; tested by alternating the light from one eye to the other and comparing the direct light reactions. (05 Mar 2000) |
| relative aperture | <microscopy> The ratio of the focal length of a lens to the diameter of its entrance pupil. This gives a number known as the f-number, usually written f:8, f:16, etc. Thus, if the focal length is divided by the number 8, 16, etc., the result will be the diameter of the entrance pupil of the lens, or if the diaphragm of the lens is wide open it will be very nearly the diameter of the free aperture of the lens. See: F-number. (05 Aug 1998) |
| relative basal area | An estimate of basal area for trees, such as produced by the Bitterlich sampling technique. (09 Oct 1997) |
| relative biological effectiveness | The ratio of radiation dosages required to produce identical change based on a formula comparing other types of radiation with that of gamma or roentgen rays. (12 Dec 1998) |
| relative dehydration | Water deficit relative to content of solutes contributing effective osmotic pressure; a state of increased effective osmotic pressure of body fluids. (05 Mar 2000) |
| relative immunity | A modified, not completely effective resistance that results when there is a sort of "fluctuating equilibrium" between the defense mechanisms of the host and the infective agent. (05 Mar 2000) |
| relative incompetence | Imperfect closure of a cardiac valve, in consequence of excessive dilation of the corresponding cavity of the heart. (05 Mar 2000) |