| 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) |
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| 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) |
| neuroectodermal tumour, primitive | A malignant brain tumour sharing common features and biologic properties with medulloblastoma. Some pathologists and clinicians use the terms interchangeably: they both can disseminate throughout the nervous system and, in some cases, systemically. most lesions arise from the posterior fossa in children under five years of age. The tumour often produces hydrocephalus and symptoms of increased intracranial pressure. Papilledema is often present. (12 Dec 1998) |
| adenoid tissue | A structure found within the lymphatic system that consists of lymphocytes within a network of fibres. (09 Oct 1997) |
| adipose tissue | <anatomy> Connective tissue that has been specialised to store fat. See: adipocyte. (25 Jun 1999) |
| aerenchymous tissue | A type of plant tissue in which cells are unusually large, resulting in large air spaces in the plant organ, such tissues are often referred to as spongy and usually provide increased buoyancy. (09 Oct 1997) |
| areolar tissue | Loose, irregularly arranged connective tissue that consists of collagenous and elastic fibres, a protein polysaccharide ground substance, and connective tissue cells (fibroblasts, macrophages, mast cells, and sometimes fat cells, plasma cells, leukocytes, and pigment cells). (05 Mar 2000) |
| bone tissue | A connective tissue, the matrix of which consists of collagen fibres and ground substance and in which are deposited calcium salts (phosphate, carbonate, and some fluoride) in the form of an apatite. Synonym: bone tissue. (05 Mar 2000) |
| border tissue movements | The action of the muscles and other tissues adjacent to the borders of a denture. (05 Mar 2000) |
| brain tissue transplantation | Transference of brain tissue, either from a foetus or from a born individual, between individuals of the same species or between individuals of different species. (12 Dec 1998) |
| brown adipose tissue | A thermogenic type of adipose tissue containing a dark pigment, and arising during embryonic life in certain specific areas in many mammals, including man. It is prominent in the newborn of all species in which it occurs and remains a distinct and conspicuous tissue in the adults of certain species, especially those that hibernate. It is also called brown adipose tissue. (12 Dec 1998) |
| cancellous tissue | Latticelike or spongy osseous tissue. (05 Mar 2000) |
| cardiac muscle tissue | See: cardiac muscle. (05 Mar 2000) |