| yolk cell | <cell biology> In those eggs in which the yolk is not distributed evenly (telolecithal eggs) the cells formed when cleavage reaches the yolk region can be termed yolk cells. (18 Nov 1997) |
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| yolk cells | Primitive embryonic cell's lying between the endoderm and mesoderm; they probably give rise to the endothelium of vitelline vessels. (05 Mar 2000) |
| white yolk | Yolk consisting of much finer particles than those of yellow yolk; thin layers of it lie between the zones of yellow yolk and form the latebra. (05 Mar 2000) |
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| egg yolk | The stored nutrient of the egg and the yellow portion of the egg of a bird. (12 Dec 1998) |
| yellow yolk | The chief constituent of the yolk in a bird's egg; it consists of relatively coarse particles of stored food materials and is laid down in concentric zones with interposed thin layers of white yolk. (05 Mar 2000) |
| yolk | 1. The yellow part of an egg; the vitellus. 2. <zoology> An oily secretion which naturally covers the wool of sheep. <anatomy> Yolk cord, the umbilical vesicle. See Unbilical. Origin: OE. Yolke, yelke, yolke, yelke, AS. Geoloca, geoleca, fr. Geolu yellow. See Yellow Alternative forms: yelk. Source: Websters Dictionary (01 Mar 1998) |
| yolk cleavage | Segmentation of the vitellus. (05 Mar 2000) |
| yolk membrane | The membrane enveloping the yolk; specifically, the thickened cell membrane of large-yolked ova. Synonym: ovular membrane, vitelline membrane. Sometimes used to designate the zona pellucida of a mammalian ovum. Synonym: yolk membrane. (05 Mar 2000) |
| yolk sac | <embryology, ornithology> One of the set of extra embryonic membranes, growing out from the gut over the yolk surface, in birds formed from the splanchnopleure, an outer layer of splanchnic mesoderm and an inner layer of endoderm. (18 Nov 1997) |
| yolk sac carcinoma | Malignant germ cell tumour commonly found in the ovary. The tumour arises from primitive germ cells and develops into extra-embryonic tissue resembling the yolk sac. Synonym: yolk sac carcinoma. (05 Mar 2000) |
| yolk sac tumour | An unusual and aggressive tumour of germ-cell origin that reproduces the extraembryonic structures of the early embryo. It is the most common malignant germ cell tumour found in children. It is characterised by a labyrinthine glandular pattern of flat epithelial cells and rounded papillary processes with a central capillary (schiller-duval body). The tumour is rarely bilateral. Before the use of combination chemotherapy, the tumour was almost invariably fatal. (12 Dec 1998) |
| yolk stalk | A narrow tube present in the early embryo that connects the midgut of the embryo (through the umbilical opening) to the yolk sac outside the embryo. Later in development, the yolk stalk is usually obliterated but a remnants of it may persist, most commonly as a finger-like protrusion from the small intestine known as meckel's diverticulum. Found in 2-4% of people, meckel's diverticulum may become inflamed much like the appendix and require surgical removal. The yolk stalk is also called the umbilical duct, vitelline duct, or oomphalomesenteric duct. (12 Dec 1998) |
| T-cell-rich, B-cell lymphoma | <tumour> A B-cell lymphoma in which more than 90% of the cells are of T-cell origin, masking the large cells that form the neoplastic B-cell component. See: adult T-cell lymphoma. (05 Mar 2000) |
| absorption cell | A small glass chamber with parallel sides, in which absorption spectra of solutions can be obtained. (05 Mar 2000) |
| acid cell | One of the cell's of the gastric glands; it lies upon the basement membrane, covered by the chief cell's, and secretes hydrochloric acid that reaches the lumen of the gland through fine intracellular and intercellular canals (canaliculi). Synonym: acid cell, oxyntic cell. (05 Mar 2000) |
| acidophil cell | A cell whose cytoplasm or its granules stain with acid dyes. (05 Mar 2000) |
| acinar cell | Any secreting cell lining an acinus, especially applied to the cell's of the pancreas that furnish pancreatic juice and enzymes to distinguish them from the cell's of ducts and the islets of Langerhans. Synonym: acinous cell. (05 Mar 2000) |