| critical organ | The organ or physiologic system that for a given source of radiation would first reach its legally defined maximum permissible radiation exposure as the dose of radiopharmaceutical is increased; e.g., the kidney is the critical organ when 197Hg-chlormerodrin is given. (05 Mar 2000) |
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| critical pathway | Schedules of medical and nursing procedures, including diagnostic tests, medications, and consultations designed to effect an efficient, coordinated program of treatment. (12 Dec 1998) |
| critical period | <psychology> A specific stage in animal and human development during which certain types of behaviour normally are shaped and molded for life. (12 Dec 1998) |
| critical pH | The pH range, about 5.5, at which saliva ceases to be saturated with respect to calcium and phosphate, and below which tooth mineral will dissolve. (05 Mar 2000) |
| critical point | A point at which two phases become identical; thus, at a given critical temperature and critical pressure, the liquid and gaseous state of a particular substance can no longer be differentiated. (05 Mar 2000) |
| critical point drying | <procedure> A method for preparing specimens for the scanning electron microscope that avoids the problems of shrinkage caused by normal drying procedures. Water in the specimen is replaced by an intermediate fluid, for example liquid carbon dioxide, avoiding setting up a liquid/gas interface and then the second fluid is allowed to vaporise by raising the temperature above the critical point, the temperature at which the liquid state no longer occurs. (18 Nov 1997) |
| critical pressure | The minimum pressure required to liquefy a gas at the critical temperature. (05 Mar 2000) |
| critical rate | A heart rate at which aberration or incomplete block will occur; a result of shortening of cycle length so that it barely includes the refractory period. (05 Mar 2000) |
| critical temperature | The temperature of a gas above which it is no longer possible by use of any pressure, however great, to convert it into a liquid. (05 Mar 2000) |
| critical velocity | <biology> The maximum speed a device or organism can sustain over a specified distance or length of time, or the maximum velocity against which device or organism can sustain a position over a specified length of time. <marine biology> Velocity through which a fish will not swim, creating a velocity barrier. (09 Oct 1997) |
| Sudeck's critical point | Region in the colon between the supply of the sigmoid arteries and that of the superior rectal artery. (05 Mar 2000) |
| illumination, critical | <microscopy> The formation of an image of the light source in the object field. The Nelsonian method in which the light source is imaged in the plane of the specimen. A ribbon filament or arc lamp is required to give uniform illumination, the lamp must be focusable, the filament position must be adjustable in all directions. The use of an achromatic condenser is advised. Synonym: Nelson illumination. (13 Jan 1998) |