| protective zone | The time in the cardiac cycle, immediately following the vulnerable period, during which a second stimulus will prevent the initiation of ventricular fibrillation by a previous stimulus applied during the vulnerable period, probably by blocking a reentrant pathway. (05 Mar 2000) |
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| X zone | A transient adrenocortical zone present in some rodents at birth, most notably in mice, situated between the zona reticularis and the adrenal medulla; it degenerates in males with the secretion at puberty and in females during their first pregnancy; it slowly enlarges in unmated females after puberty and does not degenerate until middle age; the X zone appears to secrete no hormone. Synonym: androgenic zone. Misnomer for the foetal adrenal cortex of primates. Synonym: foetal reticularis. (05 Mar 2000) |
| secondary X zone | An adrenocortical zone, situated in the inner zona fasciculata, that appears upon postpubertal gonadectomy in some male rodents, most notably the mouse; the development of this zone is believed to be stimulated by pituitary gonadotropins. (05 Mar 2000) |
| segmental zone | In a young embryo, the thickened dorsal portion of the undifferentiated paraxial mesoderm which becomes metamerically divided to form the mesodermal somites. Synonym: segmental plate. (05 Mar 2000) |
| pupillary zone | The central region of the anterior surface of the iris located between the collarette and the pupillary margin. Synonym: zona pupillaris. (05 Mar 2000) |
| Spitzka'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) |
| neutral zone | In dentistry, the potential space between the lips and cheeks on one side and the tongue on the other; natural or artificial teeth in this zone are subject to equal and opposite forces from the surrounding musculature. (05 Mar 2000) |
| subplasmalemmal dense zone | An electron-dense, 10-15 nm thick layer of highly cross-linked protein on the cytoplasmic surface of the cell membrane of epidermal corneocytes; it is highly resistant to proteolytic agents. Synonym: subplasmalemmal dense zone. (05 Mar 2000) |
| sudanophobic zone | A zone of cells, at the periphery of the zona fasciculata in the adrenal cortex of the rat, that is not stained by Sudan dyes. (05 Mar 2000) |
| nucleolar zone | <molecular biology> Loop of DNA that has multiple copies of rRNA genes. See: nucleolus. (18 Nov 1997) |
| dolorogenic zone | A specific point or area where, if stimulated by touch, pain, or pressure, a painful response will be induced. Synonym: dolorogenic zone, trigger area, trigger zone. (05 Mar 2000) |
| interpalpebral zone | The exposed area of the cornea and sclera between the lids of the open eye. (05 Mar 2000) |
| intertubular zone | The dentinal matrix which lies between zone's of peritubular dentin; it is less calcified and contains larger collagen fibres than does peritubular dentin. (05 Mar 2000) |
| isoelectric zone | The range of H-ion concentration (pH) over which isoelectric precipitation occurs. (05 Mar 2000) |
| isopycnic zone | <chemistry> The region in density gradient centrifugation having the same density as the buoyant density of the macromolecule. (05 Mar 2000) |