| RET | reticular; reticulocyte; retina; retention; retained; right esotropia |
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| RF | radial fiber; radio frequency; receptive field; regurgitant fraction; Reitland-Franklin [unit]; rela... |
| RL | radial line; radiation laboratory; reduction level; renal dysplasia-limb defects [syndrome]; resisti... |
| RMC | reticular magnocellular [nucleus]; right middle cerebral [artery] |
| RN | radionuclide; red nucleus; Registered Nurse; registry number; residual nitrogen; reticular nucleus |
| descending part of facial canal | Second portion of the facial canal, after the horizontal parts, beginning at the posterior end of the lateral crus where the canal begins to descend. It runs vertically downward, ending at the stylomastoid foramen. Anteriorly, the descending part of the facial canal communicates with the tympanic cavity via the canaliculus for the nerve to the stapedius muscle and the posterior canaliculus of the chorda tympani. (05 Mar 2000) |
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| descending posterior branch | The descending posterior branch of the superior lobar branch of the right pulmonary artery. Synonym: ramus posterior descendens. (05 Mar 2000) |
| descending scapular artery | <anatomy, artery> Origin, subclavian or as the deep branch of the transverse cervical; distribution, passes deep to the rhomboid muscles, supplying them and other muscles and skin along the vertebral border of the scapula; anastomoses, suprascapular and scapular circumflex. Synonym: arteria dorsalis scapulae, rami profundi arteriae transversae cervicis, ramus profundus arteriae transversae colli, arteria scapularis dorsalis, arteria scapularis descendens, deep branch of the transverse cervical artery, descending scapular artery, ramus profundus arteria scapularis descendens. (05 Mar 2000) |
| descending tract of trigeminal nerve | <anatomy, nerve> A compact fibre bundle, comma-shaped on transverse section, composed of primary sensory fibres of the portio major of the trigeminal nerve, descending from the level of the entrance of the trigeminus in the upper pons down through the dorsolateral region of the rhombencephalic tegmentum along the lateral side of the descending or spinal nucleus of the trigeminus, emerging on the dorsolateral surface of the lower medulla oblongata as the tuberculum cinereum, and continuing as far as the second cervical segment of the spinal cord. Its fibres are distributed to the descending or spinal nucleus of the trigeminus. Synonym: tractus spinalis nervi trigemini, descending tract of trigeminal nerve, tractus descendens nervi trigemini. (05 Mar 2000) |
| absolute system of units | A system based on absolute units accepted as being fundamental (length, mass, time) and from which other units (force, energy or work, power) are derived; such system's in common use are the foot-pound-second, centimeter-gram-second, and meter-kilogram-second system's. (05 Mar 2000) |
| absorbent system | <anatomy> The tissues and organs (including the bone marrow, spleen, thymus and lymph nodes) that produce and store cells that fight infection and the network of vessels that carry lymph. (12 May 1997) |
| alimentary system | The organs that are responsible for getting food into and out of the body and for making use of food to keep the body healthy. These include the mouth, oesophagus, stomach, liver, gallbladder, pancreas, small intestine, colon, and rectum. (12 Dec 1998) |
| anterolateral system | A composite bundle of fibres, located in the ventrolateral part of the lateral funiculus, containing spinothalamic, spinohypothalamic, spinoreticular, and spinomesencephalic (spinotectal, spinal to periaqueductal grey, etc.) fibres; occupies the combined areas of the spinal white matter historically divided into anterior and lateral spinothalamic tracts; located in white matter ventral to the denticulate ligament, hence the anatomical basis for the anterolateral cordotomy; concerned with the transmission of nociceptive and thermal information and with crude (nondiscriminative) touch. (05 Mar 2000) |
| anti-allergic and respiratory system agents | A collective term for drugs used to treat allergic reactions as well as those drugs that produce an effect on the respiratory system. (12 Dec 1998) |
| arch-loop-whorl system | See: Galton's system of classification of fingerprints. (05 Mar 2000) |
| association system | Groups or tracts of nerve fibres interconnecting different regions of one and the same major subdivision of the central nervous system, such as the various areas of the cerebral cortex or the various segments of the spinal cord. (05 Mar 2000) |
| autonomic nervous system | <anatomy> Neurons that are not under conscious control, comprising two antagonistic components, the sympathetic and parasympathetic nervous systems. The autonomic nervous system regulates key functions including the activity of the cardiac (heart) muscle, smooth muscles (e.g., of the gut), and glands. The autonomic nervous system has two divisions: 1. The sympathetic nervous system that accelerates the heart rate, constricts blood vessels, and raises blood pressure. 2. The parasympathetic nervous system slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles. (03 Jul 1999) |
| autonomic nervous system diseases | Diseases that have their major effects on the autonomic nervous system. The autonomic nervous system may be seriously affected in many other disorders including other peripheral nervous system diseases, infectious diseases (e.g., tetanus, diphtheria), immunologic diseases (e.g., acquired immunodeficiency syndrome), and systemic disorders (e.g., diabetic neuropathy, amyloid neuropathy, thyroid diseases). Disorders of central autonomic control also contribute substantially to a wide variety of problems (e.g., eating disorders, panic disorder, water-electrolyte imbalance, cardiovascular diseases). (12 Dec 1998) |
| balanced lethal system | <genetics> A population with non-linked, recessive alleles of a gene, where an individual who has two copies of the recessive allele and is therefore homozygous is dead, while an individual who has only one copy of it, and one copy of a different allele (and is heterozygous) survives. (09 Oct 1997) |
| Bethesda system | Recent classification for categorizing cervical Papanicolaou smears. Origin: Bethesda, Maryland, site of NIH (05 Mar 2000) |