- A segment; any encircling or beltlike structure, either external or internal, longitudinal or transverse. SEE ALSO: area, band, region, space, spot. SYN: zona (1) [TA]. [L. zona]- anal transitional z. [TA] region of anal canal in which the epithelium changes from the simple columnar epithelium of a mucosa to the stratified squamous epithelium of the anoderm (skin); this region is susceptible to a variety of carcinomas. SYN: zona transitionalis analis [TA].- androgenic z. 1. SYN: X z. (1). 2. SYN: fetal reticularis (2). SYN: fetal adrenal cortex. [Named in the belief (as yet unsubstantiated) that the cells within this z. secrete androgens.]- arcuate z. the inner third of the basilar membrane of the cochlear duct extending from the tympanic lip of the osseous spiral lamina to the outer pillar cell of the spiral organ (of Corti). SYN: zona arcuata, zona tecta.- Barnes z. the lower fourth of the pregnant uterus, attachment of the placenta to any part of which may cause dangerous hemorrhage. SYN: cervical z..- ciliary z. the outer, wider z. of the anterior surface of the iris, separated from the pupillary z. by the collarette. SYN: zona ciliaris.- comfort z. the temperature range between 28°C and 30°C at which the naked body is able to maintain the heat balance without either shivering or sweating; in the clothed body the range is from 13°C to 21°C.- zones of discontinuity concentric zones of varying optical density in the lens of the eye, as seen in slitlamp biomicroscopy.- dolorogenic z. SYN: trigger point.- entry z. the area of the dorsal funiculus of the spinal cord, medial to the tip of the posterior horn, in which the entering fibers of the posterior nerve root divide into ascending and descending branches.- epileptogenic z. a cortical region that on stimulation reproduces the patient's spontaneous seizure or aura.- equivalence z. in a precipitin reaction, the z. in which neither antibody nor antigen is in excess. SEE ALSO: precipitation. SYN: equivalence point.- erogenous z., erotogenic z. areas of the body, such as genitals and nipples, which elicit sexual arousal when stimulated.- gingival z. that portion of the oral mucosa which surrounds the teeth and is firmly attached to the underlying alveolar bone.- Golgi z. 1. part of the cytoplasm occupied by the Golgi apparatus; 2. in secretory cells of exocrine glands, a z. between the nucleus and the luminal surface.- grenz z. (grents) in histopathology, a narrow layer beneath the epidermis that is not infiltrated or involved in the same way as are the lower layers of the dermis. [Ger. Grenze, borderline, boundary]- hemorrhoidal z. the part of the anal canal that contains the rectal venous plexus. SYN: anulus hemorrhoidalis, zona hemorrhoidalis.- zones of hypothalamus [TA] rostrocaudally oriented regions of the hypothalamus characterized by their position and cell groups. The periventricular z. [TA] (zona periventricularis [TA]) is a thin sheet of small neurons located in the wall of the third ventricle. The medial z. [TA] (zona medialis [TA]) lies between the periventricular z. and a rostrocaudal line drawn between the mammillothalamic tract and the postcommissural fornix, and consists of supraoptic, tuberal, and mammillary regions. The lateral z. [TA] (zona lateralis [TA]) is lateral to the medial zones, and contains the tuberal nuclei and the fibers of the medial forebrain bundle. SYN: zonae hypothalamicae [TA].- inner z. of renal medulla [TA] apical portion of renal pyramids, including renal papilla. SYN: zona interna medullae renalis [TA].- intermediate z. of iliac crest [TA] the line on the crest of the ilium between the outer and inner lips, for origin of internal oblique muscle. SYN: linea intermedia cristae iliacae [TA], intermediate line of iliac crest.- intertubular z. the dentinal matrix that lies between zones of peritubular dentin; it is less calcified and contains larger collagen fibers than does peritubular dentin.- isoelectric z. the range of H+ ion concentration (pH) over which isoelectric precipitation occurs.- isopycnic z. the region in density gradient centrifugation having the same density as the buoyant density of the macromolecule.- language z. a large area of the cerebral cortex on the left side (in right-handed persons) considered by some to embrace all the centers of memories and associations connected with language.- latent z. 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.- mantle z. 1. SYN: mantle layer. 2. a layer of small B lymphocytes surrounding the paler-staining germinal centers of lymphoid follicles.- Marchant z. the area on the sphenoid and occipital bones at the base of the skull from which the dura mater is readily detached.- marginal z. 1. A z. between the red and white pulp of the spleen containing numerous macrophages and a rich plexus of sinusoids supplied by white pulp arterioles carrying blood-borne antigens. 2. SYN: marginal layer.- motor z. that portion of the cerebral cortex, primarily the posterior region of the frontal lobe, near the central sulcus, which when stimulated produces a movement and when injured produces spasticity or paralysis.- neutral z. 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 z. are subject to equal and opposite forces from the surrounding musculature.- Obersteiner-Redlich z. the narrow line along the course of a nerve (or nerve root) where the Schwann cells and connective tissue that support its axons are replaced by glia cells. The z. marks the true boundary between the central and the peripheral nervous system. Usually located at or near the surface of the spinal cord or brainstem, it can extend ( e.g., in the eighth nerve) several millimeters out along the nerve. SYN: Obersteiner-Redlich line.- outer z. of renal medulla [TA] basal portion of renal pyramid. SYN: zona externa medullae renalis [TA].- pectinate z. the outer two-thirds of the basilar membrane of the cochlear duct. SYN: zona pectinata.- peritubular z. the dentinal matrix surrounding the odontoblastic process; it is more highly calcified and contains finer collagen fibers than does the rest of the dentinal matrix.- periventricular z. [TA] See zones of hypothalamus. SYN: zona periventricularis [TA].- protective z. 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.- pupillary z. the central region of the anterior surface of the iris located between the collarette and the pupillary margin. SYN: zona pupillaris.- secondary X z. an adrenocortical z., situated in the inner zona fasciculata, that appears upon postpubertal gonadectomy in some male rodents, most notably the mouse; the development of this z. is believed to be stimulated by pituitary gonadotropins.- segmental z. in a young embryo, the thickened dorsal portion of the undifferentiated paraxial mesoderm that becomes metamerically divided to form the mesodermal somites. SYN: segmental plate.- subplasmalemmal dense z. SYN: corneocyte envelope.- sudanophobic z. a z. of cells, at the periphery of the zona fasciculata in the adrenal cortex of the rat, that is not stained by Sudan dyes.- thymus-dependent z. SYN: paracortex.- transformation z. z. on the cervix at which squamous epithelium and columnar epithelium meet; changes location in response to a woman's hormonal status.- transitional z. 1. the equatorial region of the lens of the eye where the anterior epithelial cells become transformed into lens fibers; 2. that portion of a scleral contact lens between the corneal and scleral sections.- transitional z. of lips [TA] hairless thin skin beginning at the vermillion border of the lips; appears red because of underlying capillary bed.- vascular z. an area in the external acoustic meatus where a number of minute blood vessel s enter from the mastoid bone. SYN: spongy spot, zona vasculosa.- z. 1, 2, 3, 4 of West in pulmonary physiology, defines the levels in a vertical lung according to the relationships of alveolar gas pressure, capillary blood pressure, and pulmonary venous pressure.- X z. 1. a transient adrenocortical z. 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 z. appears to secrete no hormone; SYN: androgenic z. (1). 2. misnomer for the fetal adrenal cortex of primates. SYN: fetal reticularis (3).
* * *zone 'zōn n1) an encircling anatomical structure2) a region or area set off as distinct
* * *(zōn) [Gr. zōnē a belt, girdle] a region or area, especially one with specific characteristics or boundary; called also zona. zonal adj
Medical dictionary. 2011.