| DLT | dihydroepiandrosterone loading test; double lung transplantation; double-lumen endotracheal tube |
|---|---|
| dpdt | double-pole double-throw [switch] |
| DRID | double radial immunodiffusion; double radioisotope derivative |
| DS | dead air space; dead space; deep sedative; deep sleep; defined substrate; dehydroepiandrosterone sul... |
| DV | dependent variable; diagnostic variable; difference in volume; digital vibration; dilute volume; dis... |
impedence test
| re-entrant mechanism | The probable basis of most arrhythmias, requiring at least three criteria in the heart: 1. A loop circuit, 2. Unidirectional block, 3. Slowed conduction. Impulses enter the loop circuit and divide in both directions (blocked in one direction only), negotiate the loop circuit to the area of block where the slowed conduction has allowed the impulse to arrive at a time when the tissue proximal to the unidirectional block has recovered and will permit its passage in the opposite direction. (05 Mar 2000) |
|---|---|
| mechanism | The manner of combination of parts, processes, etc., which subserve a common function. Origin: Gr. Mechan = machine (18 Nov 1997) |
| mechanism-based inhibitor | A competitive inhibitor that is converted to an irreversible inhibitor at the active site of the enzyme. Synonym: mechanism-based inhibitor. (05 Mar 2000) |
| rolling circle mechanism | <molecular biology> A mechanism of DNA replication in many viral DNAs, in bacterial f factors during mating and of certain DNAs in gene amplification in eukaryotes. DNA synthesis starts with a cut in the + strand at the replication origin, the 5' end rolls out and replication starts at the 3' side of the cut around the intact circular DNA strand. Replication of the 5' end (tail) takes place by the formation of Okazaki fragments. (18 Nov 1997) |
| ping-pong mechanism | A special multisubstrate reaction in which, for a two-substrate, two-product (i.e., bi-bi) system, an enzyme reacts with one substrate to form a product and a modified enzyme, the latter then reacting with a second substrate to form a second, final product, and regenerating the original enzyme. An example of such a mechanism is found in the aminotransferases. More complex ping-pong mechanisms exist for enzymes having more than two substrates. Synonym: double displacement mechanism. (05 Mar 2000) |
| countercurrent mechanism | A system in the renal medulla that facilitates concentration of the urine as it passes through the renal tubules. See: countercurrent exchanger, countercurrent multiplier. (05 Mar 2000) |
| pressoreceptive mechanism | The pressoreceptor system, especially of the carotid sinuses and aortic arch. (05 Mar 2000) |
| proprioceptive mechanism | <physiology> The mechanism of sense of position and movement, by which muscular movements can be adjusted to a great degree of accuracy and equilibrium maintained. (05 Mar 2000) |
| Schultze's mechanism | Expulsion of the placenta with the foetal surface foremost. (05 Mar 2000) |
| defense mechanism | A psychological means of coping with conflict or anxiety, e.g., conversion, denial, dissociation, rationalization, repression, sublimation, the psychic structure underlying a coping strategy, immunological mechanism vs. Non-specific defense mechanism. (05 Mar 2000) |
| Douglas mechanism | Mechanism of spontaneous evolution in transverse lie; extreme lateral flexion of the vertebral column with birth of the lateral aspect of thorax before the buttocks. (05 Mar 2000) |
| Duncan's mechanism | Passage of the placenta from the uterus with the rough side foremost. (05 Mar 2000) |
| immunological mechanism | The groups of cells (chiefly lymphocytes and cells of the reticuloendothelial system) that function in establishing active acquired immunity (induced sensitivity, allergy). (05 Mar 2000) |
| ordered mechanism | A scheme for substrate binding and product release for multisubstrate enzymes; for a two-substrate two-product enzyme with an ordered mechanism, one particular substrate has to bind to the enzyme first followed by the other substrate; chemistry then occurs, products are formed and are released from the enzyme in a distinct order. More complex ordered schemes exist for enzymes having more than two substrates. Some of the dehydrogenases have such a mechanism. Synonym: ordered. (05 Mar 2000) |
| ordered on-random off mechanism | A scheme for substrate binding and product release for multisubstrate enzymes; for a two-substrate two-product enzyme with this mechanism, the individuals have to bind to the enzyme in a distinct order; however, once the products are formed they may dissociate from the enzyme in either order. It has been suggested that pyruvate kinase has such a mechanism. The random on-ordered off mechanism is simply the reverse of this mechanism. (05 Mar 2000) |