| segmental sphincter | A sphincter of a segment of an organ, a tube, or a canal, and longer than an annular sphincter. (05 Mar 2000) |
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| segmental tubule | An excretory tubule of the mesonephros. Synonym: segmental tubule. (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) |
| segmentation | <biology> Organisation of the body into repeating units called segments is a common feature of several phyla, for example arthropods and annelids, although the segments arise by very different mechanisms. Segmentation also occurs during embryonic development in vertebrates, for example partition of the mesoderm into somites and is a feature of early CNS development. See: rhombomeres, neuromeres. (18 Nov 1997) |
| segmentation cavity | The cavity in the blastula of a developing embryo. Synonym: blastocoele, cleavage cavity, segmentation cavity. Origin: blasto-+ G. Koilos, hollow (05 Mar 2000) |
| segmentation gene | <molecular biology> Genes required for the establishment of segmentation in the embryo. In Drosophila about 20 such genes are required. A development pattern of the embryo of the fruit fly Drosophila where the embryo looks like a stack of discs. Each disc is a segment, and each segment consists of two compartments (an anterior and posterior). Various parts of the adult fruit fly (wings, legs, eyes, etc.) arise from specific segments. (09 Oct 1997) |
| segmentation nucleus | The compound nucleus in the impregnated ovum, formed by conjugation of the nuclei of the ovum and spermatozoon (female and male pronuclei), the zygote nucleus after it commences the first cleavage division. (05 Mar 2000) |
| segmentectomy | Excision of a segment of any organ or gland. (05 Mar 2000) |
| segmented cell | A polymorphonuclear leukocyte matured beyond the band cell so that two or more lobes of the nucleus occur. (05 Mar 2000) |
| segmented leukocyte | Any mature polymorphonuclear leukocyte, especially a neutrophilic leukocyte. (05 Mar 2000) |
| segmented neutrophil | A fully matured neutrophil that has at least 2 (and as many as 5) distinct lobes in the nucleus and manifests active ameboid motion. Synonym: mature neutrophil. (05 Mar 2000) |
| segmenter | A schizont; usually applied to the malaria parasite developing in a red blood cell after having undergone nuclear and cytoplasmic division, just before cell rupture and release of the merozoites. (05 Mar 2000) |
| Segmentina | A genus of freshwater pulmonate snails (family Planorbidae, subfamily Segmentininae); includes the species Segmentina hemisphaerula, an important intermediate host of Fasciolopsis buski. Origin: L. Segmentum, fr. Seco, to cut (05 Mar 2000) |
| segmenting body | A sporozoan trophozoite (vegetative form) that reproduces by schizogony, producing a varied number of daughter trophozoites or merozoites. See: meront, segmenter. Synonym: agamont, segmenting body. Origin: schizo-+ G. On (ont-), a being (05 Mar 2000) |
| segments of liver | Territories of the liver with independent portobilioarterial distribution or independent venous drainage. The naming of segments in the NA is based upon the portobilioarterial distribution. See: anterior segment, lateral segment, medial segment, posterior segment. Synonym: segmenta hepatis, segments of liver. (05 Mar 2000) |