| primary immune response | <immunology> The immune response to the first challenge by a particular antigen. Usually less extensive than the secondary immune response, being slower and shorter lived with smaller amounts of lower affinity antibody being produced. (18 Nov 1997) |
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| primary interatrial foramen | In the embryonic heart, the temporary opening between right and left atria situated between the lower margin of the septum primum and the atrioventricular canal cushions, in an adult heart, the abnormal persistence of the so-named communication which is normal in young embryos. Synonym: foramen subseptale, ostium primum, primary interatrial foramen. (05 Mar 2000) |
| primary labial groove | A furrow between the developing lip and gum. Synonym: labiodental sulcus, lip sulcus, primary labial groove. (05 Mar 2000) |
| primary lateral sclerosis | Considered by many to be a subgroup of motor neuron disease; a slowly progressive degenerative disorder of the motor neurons of the cerebral cortex, resulting in widespread weakness on an upper motor neuron basis; spasticity, hyperreflexia, and Babinski signs are present, but not fasciculation potentials, nor any electrodiagnostic evidence of a lower motor neuron lesion. Synonym: lateral spinal sclerosis. (05 Mar 2000) |
| primary lymphedema | A form of lymphedema observed chiefly in young women and girls, characterised by diffuse swelling of the lower extremities. Synonym: lymphedema praecox. (05 Mar 2000) |
| primary lymphoid tissue | <anatomy> Tissue that is particularly rich in lymphocytes (and accessory cells such as macrophages and reticular cells), particularly the lymph nodes, spleen, thymus, Peyer's patches, pharyngeal tonsils, adenoids and (in birds) the Bursa of Fabricius. Central lymphoid tissue: A term occasionally used as synonym for primary lymphoid tissue but should be avoided to prevent confusion between anatomical location, which is irrelevant and centrality in the system. Peripheral lymphoid tissue: Secondary lymphoid tissue, not necessarily located peripherally. Primary lymphoid tissue: Lymphoid tissues in which immune cells develop as opposed to the secondary or peripheral lymphoid tissues in which antigen independent or antigen dependent stages of maturation take place and in which responsive lymphocytes are found. Primary lymphoid tissues are foetal liver, adult bone marrow and thymus (and Bursa of Fabricius in birds). Secondary tissues are lymph nodes, spleen, tonsils and mucosa associated lymphoid tissue. (20 Mar 1998) |
| primary lysosome | <cell biology> A lysosome before it has fused with a vesicle or vacuole. Origin: Gr. Soma = body (18 Nov 1997) |
| primary lysosomes | Lysosome's produced at the Golgi apparatus where hydrolytic enzymes are incorporated; they fuse with phagosomes or pinosomes to become secondary lysosome's. (05 Mar 2000) |
| primary macular atrophy of skin | Atrophoderma in which the skin becomes bag like and wrinkled. Synonym: atrophia maculosa varioliformis cutis, atrophoderma maculatum, macular atrophy, primary idiopathic macular atrophy, primary macular atrophy of skin. Origin: G. Anetos, relaxed, + derma, skin (05 Mar 2000) |
| primary medical care | Care of a patient by a member of the health care system who has initial contact with the patient. (05 Mar 2000) |
| primary megaureter | A peristaltic segment of distal ureter, that has no anatomical obstruction, but become dilated. It may be nonobstructive or related to congenital distal ureteral obstruction, UPJ obstruction or reflux. Occurs predominantly in males (80%), left more than right, 20% of cases are bilateral, and is really a diagnosis by exclusion. (21 Jun 2000) |
| primary meristem | <plant biology> The meristem at the tips of stems and roots. Composed of undifferentiated cells, many of which divide to add to the plant body but the central mass (the quiescent centre) remains inert and only becomes active if the meristem is damaged. Synonym: eumeristem. (18 Nov 1997) |
| primary mesoderm | Extraembryonic ectoderm cells or tissues which, though derived from the zygote, are not part of the embryo proper and along with the extraembryonic mesoderm form the foetal membranes (e.g., amnion). Synonym: primary mesoderm. (05 Mar 2000) |
| primary metabolism | Metabolic processes central to most cells; e.g., biosynthesis of macromolecules, energy production, turnover, etc. (05 Mar 2000) |
| primary metabolite | A metabolite excreted during the growth phase. (09 Oct 1997) |