| DCX | double charge exchange |
|---|---|
| e | base of natural logarithms, approximately 2.7182818285; egg transfer; ejection; electric charge; ele... |
| ET | educational therapy; effective temperature; ejection time; embryo transfer; endothelin; endotoxin; e... |
| EVFMG | exchange visitor foreign medical graduate |
| exch | exchange |
| energy coupling | <chemistry> The tranfer of energy produced in one reaction to another. (09 Oct 1997) |
|---|---|
| excitation contraction coupling | <physiology> Name given to the chain of processes coupling excitation of a muscle by the arrival of a nervous impulse at the motor end plate to the contraction of the filaments of the sarcomere. The crucial link is the release of calcium from the sarcoplasmic reticulum and the analogy is often drawn between this and stimulus secretion coupling, that also involves calcium release into the cytoplasm. (18 Nov 1997) |
| fixed coupling | Where several premature beats are seen, the interval between each of them and the preceding normal beat is constant. Synonym: constant coupling. Variable coupling, where several extrasystoles are seen, the interval between each of them and the preceding sinus beat varies. (05 Mar 2000) |
| anion exchange | The process by which an anion in a mobile (liquid) phase exchanges with another anion previously bound to a solid, positively charged phase, the latter being an anion exchanger. It takes place when Cl- is exchanged for OH- in desalting. The reaction is Cl- (in solution) + (OH- on anion exchanger+) → (Cl- on anion exchanger) + OH- (in solution); combined with cation exchange, NaCl is removed from solution. Anion exchange may also be used chromatographically, to separate anions, and medicinally, to remove an anion (e.g., Cl-) from gastric contents or bile acids in the intestine. (05 Mar 2000) |
| anion exchange resin | <chemistry> A resin with fixed cationic groups which is used in chromatography to separate anionic molecules. A High molecular weight, insoluble polymers that contain functional anionic groups capable of undergoing exchange reactions. These resins are used for ion exchange chromatography, as gastric antacids, hypocholesteraemics, etc. (14 Aug 2000) |
| maternal-foetal exchange | Exchange of substances between the maternal blood and the foetal blood through the placental barrier. It excludes microbial or viral transmission. (12 Dec 1998) |
| cation exchange | The process by which a cation in a liquid phase exchanges with another cation present as the counter-ion of a negatively charged solid polymer (cation exchanger). A cation-exchange reaction in removal of the Na+ of a sodium chloride solution is RSO3-H+ + Na+ → RSO3-Na+ + H+ (R is the polymer, RSO3- is the cation exchanger); if this is combined with the anion-exchange reaction, NaCl is removed from the solution (desalting). Cation exchange may also be used chromatographically, to separate cations, and medicinally, to remove a cation; e.g., H+, from gastric contents, or Na+ and K+ in the intestine. See: anion exchange. (05 Mar 2000) |
| cation-exchange resin | See: cation exchange, cation exchanger. (05 Mar 2000) |
| cation exchange resins | High molecular weight insoluble polymers which contain functional cationic groups that are capable of undergoing exchange reactions; used in various types of chromatography; also to treat hyperkalaemia. (12 Dec 1998) |
| respiratory exchange ratio | The ratio of the net output of carbon dioxide to the simultaneous net uptake of oxygen at a given site, both expressed as moles or STPD volumes per unit time; in the steady state, respiratory exchange ratio is equal to the respiratory quotient of metabolic processes. (05 Mar 2000) |
| charge exchange | <radiobiology> Phenomenon in which an ion colliding with a molecule (or an atom) neutralises itself by capturing an electron from the molecule or atom, and transforming the molecule or atom into a positive radical or ion. (13 Nov 1997) |
| chromatography, ion exchange | Separation technique in which the stationary phase consists of ion exchange resins. The resins contain loosely held small ions that easily exchange places with other small ions of like charge present in solutions washed over the resins. (12 Dec 1998) |
| plasma exchange | Removal of plasma and replacement with various fluids, e.g., fresh frozen plasma, plasma protein fractions (ppf), albumin preparations, dextran solutions, saline. Used in treatment of autoimmune diseases, immune complex diseases, diseases of excess plasma factors, and other conditions. (12 Dec 1998) |
| pulmonary gas exchange | The exchange of oxygen and carbon dioxide between alveolar air and pulmonary capillary blood. (12 Dec 1998) |
| sister chromatid exchange | An aberrant crossing-over event in which there is an exchange of segments between the sister chromatids of a chromosome, either between the sister chromatids of a meiotic tetrad or between the sister chromatids of a duplicated somatic chromosome. It can be induced by ultraviolet and ionizing radiation or by mutagenic agents and is observed by autoradiography. (12 Dec 1998) |