| OC | obstetrical conjugate; occlusocervical; office call; on call; only child; optic chiasma; oral contra... |
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| OPO | Organ Procurement Organization |
| OS | left eye [Lat. oculus sinister]; occipitosacral; occupational safety; office surgery; Omenn syndrome... |
| OSF | organ system failure; osteoclast-stimulating factor; outer spiral fiber; overgrowth stimulating fact... |
| OTD | oculotrichodysplasia; oral temperature device; organ tolerance dose |
| electric organ | In about 250 species of electric fishes, modified muscle fibres forming disklike multinucleate plates arranged in stacks like batteries in series and embedded in a gelatinous matrix. A large torpedo ray may have half a million plates. Muscles in different parts of the body may be modified, i.e., the trunk and tail in the electric eel, the hyobranchial apparatus in the electric ray, and extrinsic eye muscles in the stargazers. Powerful electric organs emit pulses in brief bursts several times a second. They serve to stun prey and ward off predators. A large torpedo ray can produce of shock of more than 200 volts, capable of stunning a human. (storer et al., general zoology, 6th ed, p672) (12 Dec 1998) |
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| enamel organ | Epithelial cells surrounding the dental papilla and differentiated into three layers: the inner enamel epithelium, consisting of ameloblasts which eventually form the enamel, and the enamel pulp and external enamel epithelium, both of which atrophy and disappear before and upon eruption of the tooth, respectively. (12 Dec 1998) |
| end organ | The special structure containing the terminal of a nerve fibre in peripheral tissue such as muscle, tissue, skin, mucous membrane, or glands. See: ending. (05 Mar 2000) |
| Jacobson's organ | A specialised part of the olfactory system located anteriorly in the nasal cavity within the nasal septum. Chemosensitive cells of the vomeronasal organ project via the vomeronasal nerve to the accessory olfactory bulb. The primary function of this organ appears to be in sensing pheromones which regulate reproductive and other social behaviours. While the structure has been thought absent in higher primate adults, data now suggests it may be present in adult humans. (12 Dec 1998) |
| floating organ | An organ with loose attachments, permitting its displacement. Synonym: floating organ, ptotic organ. (05 Mar 2000) |
| flower-spray organ of Ruffini | One of the two types of sensory nerve ending associated with the neuromuscular spindle (the other being the annulospiral ending); in this type, the fibre branches spread out upon the surface of the intrafusal fibres like a spray of flowers. Synonym: flower-spray organ of Ruffini. (05 Mar 2000) |
| foetal organ maturity | <embryology> Functional competence of specific foetal organs or body systems. In humans, it is usually assessed by analysis of amniotic fluid, as in the assessment of foetal lung maturity by analysis for components of pulmonary surfactant. (08 Mar 2000) |
| lateral line sense organ | A structure in fish consisting of a long groove or canal extending along each side of the trunk and tail and branching in the head region; the groove or tube is lined with neuroepithelial cells, some of which are in groups known as neuromasts; its function appears to be the detection of vibrations of low frequency. Synonym: neuromast organ. (05 Mar 2000) |