| cesarian section, lower segment | A Cesarian section in which the surgical incision (cut) is made in the lower segment of the uterus. (12 Dec 1998) |
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| mesoblastic segment | 1. <zoology> One of the actual or ideal serial segments of which an animal, especially. An articulate or vertebrate, is is composed; somatome; metamere. Somitic. 2. <embryology> Segmentally arranged blocks of mesoderm lying on either side of the notochord and neural tube during development of the vertebrate embryo. Somites are formed sequentially, starting at the head. Each somite will give rise to muscle from the myotome region), spinal column (from the sclerotome) and dermis (from dermatome). (04 Mar 1998) |
| rod outer segment | <ophthalmology, physiology> Major photoreceptor cell of vertebrate retina (about 125 million in a human eye). Columnar cells (about 40m long, 1m diameter) having three distinct regions: a region adjacent to and synapsed with, the neural layer of the retina contains the nucleus and other cytoplasmic organelles, below this is the inner segment, rich in mitochondria, that is connected through a thin neck (in which is located a ciliary body) to the outer segment. The outer segment largely consists of a stack of discs membrane infoldings that are incompletely separated in cones) that are continually replenished near the inner segment and that are shed from the distal end and phagocytosed by the pigmented epithelium. The membranes of the discs are rich in rhodopsin, the pigment that absorbs light. (03 Jul 1999) |
| RST segment | The part of the electrocardiogram between the QRS complex and the T wave. Virtually never distinct in normal hearts in which it forms the initial limb of the T wave without an agreed endpoint. (05 Mar 2000) |
| posterior basal segment | Posterior basal segment of inferior lobe of right and left lungs; lies adjacent to vertebral column below superior segment. Synonym: segmentum basale posterius. (05 Mar 2000) |
| posterior segment | A delimited part or section of an organ or other structure which lies in back of or dorsal to the other similar parts or sections; 1) segmentum posterius (hepar); the posterior segment of the right lobe of the liver; 2) segmentum posterius (pulmo dexter); [S 2]; the posterior segment of the superior lobe of the right lung; 3) segmentum posterius (ren); the posterior segment of the kidney; 4) camera vitrea bulbi; vitreous camera; vitreous chamber of eye; the posterior intraocular segment of the eyeball occupied by the vitreous which lies behind the aqueous-filled anterior segment and is separated from it by the lens and zonule. Synonym: segmentum posterius. (05 Mar 2000) |
| posterior segment of eyeball | The large space between the lens and the retina; it is filled with the vitreous body. Synonym: camera vitrea bulbi, vitreous camera, vitreous chamber of eye. (05 Mar 2000) |
| P-R segment | That part of the electrocardiographic curve between the end of the P wave and the beginning of the QRS complex. (05 Mar 2000) |
| section, lower segment cesarian | A Cesarian section in which the surgical incision (cut) is made in the lower segment of the uterus. (12 Dec 1998) |
| segment | <biology> A portion of a larger body or structure, set off by natural or arbitrarily established boundaries. Origin: L. Segmentum = a piece cut off (18 Nov 1997) |
| segment long spacing | <biochemistry> Abnormal packing pattern of collagen molecules formed if ATP is added to acidic collagen solutions, in which lateral aggregates of molecules are produced. Each aggregate is 300 nm long and the molecules are all in register. If segment long spacing aggregates are overlapped with a quarter stagger, the 67 nm banding pattern of normal fibrils is reconstituted. Acronym: SLS (18 Nov 1997) |
| segment polarity gene | <molecular biology> A segmentation gene, responsible for specifying anterior posterior polarity within individual embryonic segments. In Drosophila, there are at least 10 such genes, for example gooseberry. (18 Nov 1997) |
| neural segment | Alternate swellings and constrictions seen along the neuraxis at early stages of neural tube development, thought to be evidence of intrinsic segmentation in the CNS. Neuromeres or segments in the hindbrain region are called rhombomeres and have been shown to be lineage restriction units, each constructing a defined piece of hindbrain. (18 Nov 1997) |
| S-T segment | That part of the electrocardiographic tracing immediately following the QRS complex and merging into the T wave. (05 Mar 2000) |
| subapical segment | An inconstant segment of the inferior lobe of the right and left lungs. Synonym: segmentum subapicale, segmentum subsuperius, subsuperior segment. (05 Mar 2000) |