| 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) |
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| 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) |
| primary methemoglobinaemia | Methemoglobinaemia due to formation of any one of a group of abnormal a chain or b chain haemoglobins collectively known as haemoglobin M. Slate-gray cyanosis occurs in early infancy, without pulmonary or cardiac disease, and is resistant to ascorbic acid or methylene blue therapy; autosomal dominant inheritance, methemoglobinaemia due to deficiency of cytochrome b5 reductaseor methemoglobin reductase, the enzyme responsible for reduction of intraerythrocyte methemoglobin; cyanosis is improved by ascorbic acid or methylene blue; autosomal recessive inheritance, one case of methemoglobinaemia has been reported that apparently is due to a deficiency of cytochrome b5. Synonym: hereditary methemoglobinaemia, hereditary methemoglobinaemic cyanosis, primary methemoglobinaemia. (05 Mar 2000) |
| primary myeloid metaplasia | Myeloid metaplasia occurring as the primary condition, often in association with myelofibrosis. Synonym: agnogenic myeloid metaplasia. (05 Mar 2000) |
| primary narcissism | In psychoanalysis, the original psychic energy embodied or invested in the ego. (05 Mar 2000) |
| primary neurasthenia | A form of nervous exhaustion appearing in the adolescent period. Synonym: primary neurasthenia. (05 Mar 2000) |
| primary neuroendocrine carcinoma of the skin | A rare malignant cutaneous tumour seen in sun-exposed skin of elderly patients composed of dermal nodules of small round cells with scanty cytoplasm in a trabecular pattern; the tumour cells contain cytoplasmic dense core granules resembling neurosecretory granules seen in Merkel cells. Synonym: primary neuroendocrine carcinoma of the skin, trabecular carcinoma. (05 Mar 2000) |
| primary neuronal degeneration | <disease> A progressive, neurodegenerative disease characterised by loss of function and death of nerve cells in several areas of the brain leading to loss of cognitive function such as memory and language. The cause of nerve cell death is unknown but the cells are recognised by the appearance of unusual helical protein filaments in the nerve cells (neurofibrillary tangles) and by degeneration in cortical regions of brain, especially frontal and temporal lobes. Alzheimer's disease is the most common cause of dementia. (22 May 1997) |
| primary nodule | A lymphatic nodule having small lymphocytes and lacking a germinal centre. (05 Mar 2000) |
| primary nondisjunction | Nondisjunction occurring in a previously normal cell. (05 Mar 2000) |
| primary oocyte | <cell biology, gynaecology> The enlarging ovum before maturity is reached, as opposed to the secondary oocyte or polar body. (18 Nov 1997) |
| primary organiser | The organiser situated on the dorsal lip of the blastopore. (05 Mar 2000) |