| primitive gut | A flat sheet of intraembryonic endoderm that will change into a tubular gut due to the folding of embryonic body-head, tail and lateral body folds. Synonym: archenteron, celenteron, endodermal canal, subgerminal cavity. (05 Mar 2000) |
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| primitive knot | A local thickening of the blastoderm at the cephalic end of the primitive streak of the embryo. Synonym: Hensen's knot, Hensen's node, Hubrecht's protochordal knot, primitive knot, protochordal knot. (05 Mar 2000) |
| primitive meninx | The embryonic loose mesenchymatous tissue surrounding the brain and spinal cord; from it the three definite meninges (arachnoidea, dura mater, and pia mater) are derived. Synonym: meninx primitiva. Meninx serosa, obsolete term for arachnoidea; the arachnoid is actually not a serous membrane. (05 Mar 2000) |
| primitive node | A local thickening of the blastoderm at the cephalic end of the primitive streak of the embryo. Synonym: Hensen's knot, Hensen's node, Hubrecht's protochordal knot, primitive knot, protochordal knot. (05 Mar 2000) |
| primitive palate | In the early embryo, the mesoderm-filled shelf, formed from the medial nasal process, that anteriorly separates the oral cavity below from the primitive nasal cavities above. Synonym: primitive palate. (05 Mar 2000) |
| primitive perivisceral cavity | The space between the ectoderm and endoderm in the gastrula. Synonym: primitive perivisceral cavity. (05 Mar 2000) |
| primitive pit | The depression in the primitive node that serves to connect the notochordal canal with the surface ectoderm and the yolk sac. These connections are referred to as the neurenteric canal. (05 Mar 2000) |
| primitive reticular cell | A cell with processes making contact with those of other similar cell's to form a cellular network; along with the network of reticular fibres, the reticular cell's form the stroma of bone marrow and lymphatic tissues. (05 Mar 2000) |
| primitive ridge | One of the paired ridge's on either side of the primitive groove. (05 Mar 2000) |
| primitive streak | An ectodermal ridge in the midline at the caudal end of the embryonic disk from which arises the intraembryonic mesoderm; achieved by inward and then lateral migration of cells; in human embryos, it appears on day 15 and gives a cephalocaudal axis to the developing embryo. Synonym: germinal streak. (05 Mar 2000) |
| acinar cell tumour | A solid and cystic tumour of the pancreas, occurring in young women; tumour cells contain zymogen granules. (05 Mar 2000) |
| acute splenic tumour | Acute splenitis, enlargement, and softening of the spleen, usually due to bacteraemia or severe bacterial toxaemia. (05 Mar 2000) |
| adenoid tumour | Adenoma, or neoplasm with glandlike spaces. (05 Mar 2000) |
| adenomatoid odontogenic tumour | A benign epithelial odontogenic tumour appearing radiographically as a well-circumscribed radiolucent-radiopaque lesion usually surrounding the crown of an impacted tooth in an adolescent or young adult; characterised histologically by columnar cells organised in a duct-like configuration interspersed with spindle-shaped cells and amyloid-like deposition that gradually undergoes dystrophic calcification. Synonym: adenoameloblastoma, ameloblastic adenomatoid tumour. (05 Mar 2000) |
| adenomatoid tumour | A small, circumscribed, benign tumour of the genital tract, composed of small glandlike spaces lined by flattened or cuboidal mesothelium-like cells. (12 Dec 1998) |