| RST | radiosensitivity test; reagin screen test; right sacrotransverse [fetal position]; rubrospinal tract... |
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| RTF | resistance transfer factor; respiratory tract fluid |
| RTI | respiratory tract infection; reverse transcriptase inhibition |
| RVIT | right ventricular inflow tract |
| RVOT | right ventricular outflow tract |
| lateral root of optic tract | The larger division of the posterior end of the optic tract that terminates in the lateral geniculate body. Synonym: radix lateralis tractus optici. (05 Mar 2000) |
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| lateral spinothalamic tract | The dorsal part of the spinothalamic tract, which conveys impulses associated with pain and temperature sensation. See: spinothalamic tract. Synonym: tractus spinothalamicus lateralis. (05 Mar 2000) |
| frontopontine tract | A large group of fibres arising from the frontal lobe of the cerebral hemisphere, especially the precentral gyrus, descending in the capsula interna, farther caudally composing the medial part of the crus cerebri in which they extend caudalward to end in the gray matter (pontine nuclei) of the ventral part of the pons. Synonym: tractus frontopontinus. (05 Mar 2000) |
| frontotemporal tract | A band of long association fibres reciprocally connecting the frontal and temporal lobes of the cerebrum, running caudally through the white matter of the frontal lobe, sharply curving ventrally under the stem of the sylvian fissure, and then fanning out to the cortex of the anterior half of the superior and middle temporal gyri. Synonym: fasciculus uncinatus, arcuate fasciculus, frontotemporal tract, hooked fasciculus, temporofrontal tract. (05 Mar 2000) |
| Lissauer's tract | A longitudinal bundle of thin, unmyelinated and poorly myelinated fibres capping the apex of the posterior horn of the spinal gray matter, composed of posterior root fibres and short association fibres that interconnect neighboring segments of the posterior horn. Synonym: fasciculus dorsolateralis, tractus dorsolateralis, dorsolateral tract, fasciculus marginalis, Lissauer's bundle, Lissauer's column, Lissauer's fasciculus, Lissauer's marginal zone, Lissauer's tract, marginal fasciculus, Spitzka's marginal tract, Spitzka's marginal zone, Waldeyer's tract, Waldeyer's zonal layer. (05 Mar 2000) |
| Loewenthal's tract | A bundle of thick, heavily myelinated fibres originating in the deep layers of the superior colliculus, crossing to the opposite side in the dorsal tegmental decussation, descending along the median plane, between the medial longitudinal fasciculus dorsally, the medial lemniscus ventrally, into the anterior funiculus of the spinal cord. The tract ends in the medial region of the anterior horn of the cervical spinal cord, and appears to be involved in head movements during visual and auditory tracking. Throughout its course in the brainstem it is accompanied by fibres of the tectobulbar tract. Synonym: tractus tectospinalis, Held's bundle, Loewenthal's bundle, Loewenthal's tract, Marchi's tract, predorsal bundle. (05 Mar 2000) |
| lower respiratory tract | <anatomy> The trachea, bronchi, and lungs. (09 Oct 1997) |
| lower respiratory tract smear | A group of cytologic specimens containing material from the lower respiratory tract and consisting mainly of sputum (spontaneous, induced) and material obtained at bronchoscopy (aspirated, lavaged, brushed); used for cytologic study of cancer and other diseases of the lungs. Synonym: bronchoscopic smear, sputum smear. (05 Mar 2000) |