| progress zone | An undifferentiated population of mesenchyme cells beneath the apical ectodermal ridge of the chick limb bud from which the sucessive parts of the limb are laid down in a proximo distal sequence. (18 Nov 1997) |
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| 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) |
| 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) |
| 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) |