- organ
- Any part of the body exercising a specific function, as of respiration, secretion, or digestion. SYN: organum [TA], organon. [L. organum, fr. G. organon, a tool, instrument]- annulospiral o. SYN: annulospiral ending.- Chievitz o. a normal epithelial structure, possibly a neurotransmitter, found at the angle of the mandible with branches of the buccal nerve.- circumventricular organs four small areas in or near the base of the brain that have fenestrated capillaries and are outside the blood-brain barrier. They are neurohypophysis, area postrema [TA], organum vasculosum of lamina terminalis [TA], and subfornical o. [TA] (SFO). The neurohypophysis is a neurohemal o.. The other three are chemoreceptors: area postrema triggers vomiting in response to chemical changes in plasma, organum vasculosum of the lamina terminalis senses osmolality and alters vasopressin secretion, and SFO initiates drinking in response to angiotensin II.- critical o. the o. or physiologic system that for a given source of radiation would first reach its legally defined maximum permissible radiation exposure as the dose of radiation is increased; e.g., the kidney is the critical o., receiving the most radiation, when Tc-99m dimethylsuccinic acid is given.- enamel o. a circumscribed mass of ectodermal cells budded off from the dental lamina; it becomes cup shaped and develops on its internal face the ameloblast layer of cells that produce the enamel cap of a developing tooth.- end o. the special structure containing the terminal of a nerve fiber in peripheral tissue such as muscle, tissue, skin, mucous membrane, or glands. SEE ALSO: ending.- Golgi tendon o. a proprioceptive sensory nerve ending embedded among the fibers of a tendon, often near the musculotendinous junction; it is compressed and activated by any increase of the tendon's tension, caused either by active contraction or passive stretch of the corresponding muscle. SYN: neurotendinous o., neurotendinous spindle.- gustatory o. [TA] located in the papillae of the mucous membrane of the tongue, chiefly in the vallate papillae. SYN: organum gustatorium [TA], organum gustus [TA], o. of taste.- intromittent o. SYN: penis.- Jacobson o. SYN: vomeronasal o..- neurohemal organs brain areas from which substances enter blood e.g., the neurohypophysis from which oxytocin and vasopressin enter blood.- olfactory o. [TA] the olfactory region in the superior portion of the nasal cavity. SYN: organum olfactus [TA], o. of smell.- otolithic organs the utricle and saccule of the inner ear that possess otoliths and respond to linear acceleration and deceleration, including gravity.- o. of Rosenmüller SYN: epoophoron.- sense organs [TA] the organs of special sense, including the eye, ear, olfactory o., taste organs, and the accessory structures associated with these organs. SYN: organa sensuum.- spiral o. [TA] a prominent ridge of highly specialized epithelium in the floor of the cochlear duct overlying the basilar membrane of cochlea, containing one inner row and three outer rows of hair cells, or cells of Corti (the auditory receptor cells innervated by the cochlear nerve) supported by various columnar cells: the pillars of Corti, cells of Hensen, and cells of Claudius; the spiral o. is partly overhung by an awninglike shelf, the tectorial membrane, the free marginal zone of which is covered by a gelatinous substance in which the stereocilia of the outer hair cells are embedded. SYN: organum spirale [TA], acoustic papilla, Corti o..- subcommissural o. [TA] a microscopic o., made up of columnar ciliated ependymal cells, located in the cerebral aqueduct beneath the posterior commissure of the brain; it is believed to have a neurosecretory function. SYN: organum subcommissurale.- subfornical o. (SFO) the intercolumnar tubercle. One of the circumventricular organs. SFO has fenestrated capillaries and is outside the blood-brain barrier. It is thought to be a chemoreceptor zone involved in cardiovascular regulation. SYN: organum subformicale [TA].- supernumerary organs organs exceeding the normal number, which may develop from multiple foci of organization in an o.-formative field larger (originally) than that of the definitive main o.; such organs are aberrant but frequently not a cause of disease; illness may persist if they are left in the body after therapeutic removal of the main o., e.g., accessory spleen. SYN: accessory organs (2).- target o. a tissue or o. upon which a hormone exerts its action; generally, a tissue or o. with appropriate receptors for a hormone. SYN: target (3).- urinary organs organs involved with the formation, storage, and excretion of urine. SEE ALSO: urinary system. SYN: organa urinaria.- vascular o. of lamina terminalis [TA] See circumventricular organs. SYN: organum vasculosum laminae terminalis [TA].- vestibular o. SYN: vestibular labyrinth.- vestibulocochlear o. [TA] the external, middle, and internal ear. SYN: organum vestibulocochleare [TA].- vestigial o. a rudimentary structure in humans corresponding to a functional structure or o. in the lower animals.- vomeronasal o. [TA] a fine vestigal horizontal canal, ending in a blind pouch, in the mucous membrane of the nasal septum, beginning just behind and above the incisive duct; a structure that usually regresses after the 6th month of gestation. In many lower animals, it functions as an accessory olfactory o.. SYN: organum vomeronasale [TA], Jacobson o..- wandering o. an o. with loose attachments, permitting its displacement. SYN: floating o., ptotic o..- organs of Zuckerkandl SYN: paraaortic bodies, under body.
* * *
or·gan 'ȯr-gən n a differentiated structure (as a heart or kidney) consisting of cells and tissues and performing some specific function in an organism* * *
n.a part of the body, composed of more than one tissue, that forms a structural unit responsible for a particular function (or functions). Examples are the heart, lungs, and liver.* * *
or·gan (orґgən) [L. organum (q.v.)] organum.
Medical dictionary. 2011.
