| primary cell | <cell biology> A cell or cell line taken directly from a living organism, which is not immortalised. (06 Mar 1998) |
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| primary cell culture | <cell culture> Of animal cells, the cells taken from a tissue source and their progeny grown in culture before subdivision and transfer to a sub culture. (18 Nov 1997) |
| primary cell wall | <plant biology> A plant cell wall that is still able to expand, permitting cell growth. Growth is normally prevented when a secondary wall has formed. Primary cell walls contain more pectin than secondary walls and no lignin is present until a secondary wall has formed on top of them. (06 Mar 1998) |
| primary cementum | Cementum that has no cementocytes; may cover the entire root of the tooth, but often is missing on the apical third of the root. (05 Mar 2000) |
| primary centre 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 choana | Primitive choana, initial opening of the nasal pits and olfactory sac of the embryo into the rostral part of the primordial oronasal cavity, before the formation of the secondary palate. (05 Mar 2000) |
| primary coccidioidomycosis | A disease common in the San Joaquin Valley of California and certain additional areas in the southwestern U.S. As well as the Chaco region of Argentina, caused by inhalation of the arthroconidia of Coccidioides immitis; acute onset of symptoms resemble pneumonia or pulmonary tuberculosis, productive of sputum usually containing spores of the fungus, and accompanied by aches, malaise, severe headache, and occasionally an early erythematous or papular eruption; erythema multiforme or erythema nodosum may appear; the coccidioidin test is positive. Synonym: desert fever, San Joaquin fever, San Joaquin Valley disease, San Joaquin Valley fever, valley fever. (05 Mar 2000) |
| primary colour | The three colour's of the retinal cone pigments (red, green, blue) that may be combined to match any hue. Synonym: simple colour. (05 Mar 2000) |
| primary complex | The typical lesions of primary pulmonary tuberculosis, consisting of a small peripheral focus of infection, with hilar or paratracheal lymph node involvement. (05 Mar 2000) |
| primary constriction | The narrowing between the two arms of the chromosome represented by the centromere. (05 Mar 2000) |
| primary dental lamina | dental ledge |
| primary dentin | Dentin which forms until the root is completed. (05 Mar 2000) |
| primary dentition | The set of 20 first (deciduous) teeth. The primary dentition is as opposed to the secondary (permanent) dentition. at birth, both sets of dentition are evident by X-ray. (12 Dec 1998) |
| primary deviation | The ocular deviation seen in paralysis of an ocular muscle when the nonparalysed eye is used for fixation. (05 Mar 2000) |
| primary digestion | Digestion in the alimentary tract. (05 Mar 2000) |