| zone centrifugation | <technique> High-speed centrifugation inwhich molecules float at a point wheretheir density equals that in a gradient of cesium chloride or sucrose. (12 Jan 1998) |
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| zone electrophoresis | <chemistry, procedure> A type of electrophoresis used by physical chemists. In it, the components of a mixture are separated into distinct zones by moving the solution through a porous medium such as filter paper. (06 May 1997) |
| zone of inhibition | <microbiology> The area of no bacterial browth around an antimicrobial agent in the disk-diffusion test. (09 Oct 1997) |
| zone of optimal proportion | <chemistry> A zone in a solution of mixed antigen in which the two biomolecules are totally combined. (11 May 1997) |
| zone of polarizing activity | <cell biology> The small group of mesenchyme cells in avian limb buds that is located at the posterior margin of the developing bud and that produces a substance, possibly retinoic acid, that provides positional information to the developing limb bud. (18 Nov 1997) |
| foetal zone | An extensive area of the adrenal gland present in primates during foetal life and for a short period after birth; located between the definitive cortex and the medulla, it contains large steroid-secreting cells arranged in a reticular pattern; involution of this zone in humans is largely completed by three months after birth. Synonym: androgenic zone, foetal reticularis, foetal zone, provisional cortex. (05 Mar 2000) |
| language zone | A large area of the cerebral cortex on the left side (in right-handed persons) considered by some to embrace all the centres of memories and associations connected with language. (05 Mar 2000) |
| latent zone | That portion of the cerebral cortex, the stimulation of which produces no movement and a lesion of which produces no symptoms; mainly the more anterior areas of the frontal lobes. (05 Mar 2000) |
| frontal zone contraction theory | Model proposed to account for the movement of giant amoebae in which cytoplasmic contraction at the front of the leading pseudopod (fountain zone) pulls viscoelastic cytoplasm forward in the centre of the cell and forms a tube of more rigid cytoplasm immediately below the plasma membrane behind the active region. The peripheral contracted cytoplasm relaxes into a weaker gel at the rear and is pulled forward in its turn. Contrasts with the ectoplasmic tube contraction model. (18 Nov 1997) |
| Lissauer's marginal zone | A longitudinal bundle of thin, unmyelinated and poorly myelinated fibres capping the apex of the posterior horn of the spinal gray matter, composed of posterior root fibres and short association fibres that interconnect neighboring segments of the posterior horn. Synonym: fasciculus dorsolateralis, tractus dorsolateralis, dorsolateral tract, fasciculus marginalis, Lissauer's bundle, Lissauer's column, Lissauer's fasciculus, Lissauer's marginal zone, Lissauer's tract, marginal fasciculus, Spitzka's marginal tract, Spitzka's marginal zone, Waldeyer's tract, Waldeyer's zonal layer. (05 Mar 2000) |
| abdominal pregnancy | The implantation and development of the ovum in the peritoneal cavity, usually secondary to an early rupture of a tubal pregnancy; very rarely, primary implantation may occur in the peritoneal cavity. Synonym: abdominocyesis, intraperitoneal pregnancy. (05 Mar 2000) |
| aborted ectopic pregnancy | The rupture of an oviduct, the seat of ectopic pregnancy, or extrusion of the product of conception through the fimbriated end of the oviduct; aborted ectopic pregnancy, the pregnancy having originated in the fallopian tubes. Synonym: aborted ectopic pregnancy. (05 Mar 2000) |
| alcohol, pregnancy | The consumption of alcohol during pregnancy carries the danger of damaging the foetus. (12 Dec 1998) |
| ampullar pregnancy | Tubal pregnancy situated near the midportion of the oviduct. (05 Mar 2000) |
| bigeminal pregnancy | A pregnancy that may result from the fertilization of two separate ova or of a single ovum. See: twin. Synonym: bigeminal pregnancy. (05 Mar 2000) |