| primary ovarian follicle | An ovarian follicle before the appearance of an antrum; marked by developmental changes in the oocyte and follicular cells so that the latter form one or more layers of cuboidal or columnar cells; the follicle becomes surrounded by a sheath of stroma, the theca. Synonym: folliculus ovaricus primarius. (05 Mar 2000) |
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| primary 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) |
| primary pentosuria | essential pentosuria |
| primary pigmentary degeneration of retina | A hereditary disorder of the retina mainly affecting photoreceptors and retinal pigment epithelium; a miscellaneous category including Friedreich's ataxia, Refsum's disease, and abetalipoproteinaemia. Synonym: primary pigmentary degeneration of retina. (05 Mar 2000) |
| primary point of ossification | This is the first site where bone begins to form in the shaft of a long bone or in the body of an irregular bone. Synonym: punctum ossificationis primarium, primary point of ossification. (05 Mar 2000) |
| primary prevention | Prevention of disease or mental disorders in susceptible individuals or populations through promotion of health, including mental health, and specific protection, as in immunization, as distinguished from the prevention of complications or after-effects of existing disease. (12 Dec 1998) |
| primary process | In psychoanalysis, the mental process directly related to the functions of the primitive life forces associated with the id and characteristic of unconscious mental activity; marked by unorganised, illogical thinking and by the tendency to seek immediate discharge and gratification of instinctual demands. Compare: secondary process. (05 Mar 2000) |
| primary producer | An organism that uses light to synthesise new organic material from carbon dioxide. (09 Oct 1997) |
| primary production | Production of organic substances by photosynthesis, the quantity of material so produced per unit time. (09 Oct 1997) |
| primary progressive cerebellar degeneration | A familial ataxic condition related to cerebellar degeneration. (05 Mar 2000) |
| primary pulmonary hypertension | A condition where there is increased blood pressure in the pulmonary arteries with otherwise normal heart and lungs. The cause is unknown, but there is diffuse narrowing of the pulmonary arteries resulting in increased arteriolar pressures. Secondary heart failure ensues without correction of this problem. There is an increased incidence of this disease in females between the ages of 20 and 40 years. Treatment may include a heart and lung transplant in select cases. (27 Sep 1997) |
| primary pulmonary lobule | The part of the airway consisting of a respiratory bronchiole and all of its branches. Synonym: primary pulmonary lobule, respiratory lobule. (05 Mar 2000) |
| primary pyoderma | A pyoderma, such as impetigo, in which pus formation is an essential part of the disease. (05 Mar 2000) |
| primary radiation | An incident X-ray beam. (05 Mar 2000) |
| primary reaction | <dermatology> The cutaneous and sometimes systemic reactions associated with vaccination with smallpox vaccine. (18 Nov 1997) |