| digestive tract | The passage leading from the mouth to the anus through the pharynx, oesophagus, stomach, and intestine. Synonym: alimentary canal, alimentary tract, digestive tube, tubus digestorius. (05 Mar 2000) |
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| direct pyramidal tract | Uncrossed fibres forming a small bundle in the pyramidal tract. See: pyramidal tract. Synonym: tractus corticospinalis anterior, tractus pyramidalis anterior, anterior corticospinal tract, anterior pyramidal fasciculus, direct pyramidal tract, fasciculus corticospinalis anterior, fasciculus pyramidalis anterior, Turck's bundle, Turck's column, Turck's tract. (05 Mar 2000) |
| dorsolateral 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) |
| iliopubic tract | Thickened inferior margin of the transversalis fascia seen as a fibrous band running parallel and posterior (deep) to the inguinal ligament, contributing to the posterior wall of the inguinal canal as it bridges the external iliac-femoral vessels from the iliopectineal arch to the superior pubic ramus. It marks the inferior edge of the deep inguinal ring and the medial margin of the femoral canal. Seen only when the inguinal region is viewed from its internal aspect, it is a useful landmark in laparoscopy of this region, as for repair of inguinal herniae. Synonym: deep crural arch, Thompson's ligament. (05 Mar 2000) |
| iliotibial tract | A fibrous reinforcement of the fascia lata on the lateral surface of the thigh, extending from the crest of the ilium to the lateral condyle of the tibia. Synonym: tractus iliotibialis, iliotibial band, Maissiat's band. (05 Mar 2000) |
| infection, urinary tract | An infection in the urinary system that begins when microorganisms cling to the opening of the urethra (the canal from the bladder) and begin to multiply. most utis are due to one type of bacteria, e. (escherichia) coli, a normal denisen of the colon. An infection in the urethra leads to inflammation called urethritis. From there bacteria may move up, causing a bladder infection (cystitis) and if the infection is not treated promptly, bacteria may go up the ureters to infect the kidneys (pyelonephritis). Factors leading to uti include any abnormality of the urinary tract (such as a urinary tract malformation or a kidney stone) that obstructs the flow of urine, an enlarged prostate gland that slows the flow of urine, catheters (tubes) in the bladder, diabetes (due to changes of the immune system), and any disorder that suppresses the immune system. Women have more uti than men, probably because a woman's urethra is shorter (allowing bacteria quick access to the bladder) and nearer sources of bacteria from the anus and vagina. For many women, sexual intercourse seems to trigger an infection, as may the use of a diaphragm. Not everyone with a uti has symptoms but symptoms commonly include a frequent urge to urinate and a painful, burning when urinating (dysuria). The urine may look milky or cloudy, even reddish if blood is present. Kidney infection can cause pain in the back or side below the ribs. In children, symptoms may be easily missed or misunderstood. A child with a uti may be irritable, not eat normally, have an unexplained fever, have incontinence or loose bowels, or just not thrive. (12 Dec 1998) |
| occipitocollicular tract | The system of nerve fibres by which the occipital cortex projects to the superior colliculus. Synonym: occipitocollicular tract. (05 Mar 2000) |
| occipitopontine tract | A group of fibres originating in the occipital lobe of the cerebral hemisphere and descending in the internal capsule and lateral part of the crus cerebri to the pontine nuclei or ventral part of the pons. Synonym: tractus occipitopontinus. (05 Mar 2000) |
| occipitotectal tract | The system of nerve fibres by which the occipital cortex projects to the superior colliculus. Synonym: occipitocollicular tract. (05 Mar 2000) |
| olfactory tract | A nervelike, white band composed primarily of nerve fibres originating from the mitral cells and tufted cells of the olfactory bulb but also containing the scattered cells of the anterior olfactory nucleus. The tract is closely applied to the ventral surface of the frontal lobe, and attaches itself to the base of the cerebral hemisphere at the olfactory trigone, beyond which it extends in the form of the olfactory striae which distribute their fibres to the olfactory tubercle and, in largest number, to the olfactory cortex on and around the uncus of the parahippocampal gyrus. See: olfactory nerves. Synonym: tractus olfactorius, olfactory peduncle. (05 Mar 2000) |
| olivocerebellar tract | A large group of loosely arranged fibre fascicles emerging from the hilus of the olivary nucleus, crossing to the opposite side of the medulla oblongata through the stratum interolivare lemnisci and the contralateral olive, and joining the restiform body, the larger part of the contralateral inferior cerebellar peduncle; its fibres terminate in all parts of the cerebellar cortex as climbing fibres. Synonym: tractus olivocerebellaris. (05 Mar 2000) |
| olivocochlear tract | See: olivocochlear bundle. (05 Mar 2000) |
| olivospinal tract | A slender bundle of nerve fibres in the peripheral zone of the lateral funiculus of the spinal cord, composed of spino-olivary fibres more likely than olivospinal fibres. Synonym: Helweg's bundle. (05 Mar 2000) |
| optic tract | The continuation of the optic nerve fibres beyond (behind) the latter's hemidecussation in the optic chiasm; each of the two symmetrical optic tracts is composed of fibres originating from the temporal half of the retina of the ipsilateral eye and a nearly equal number of fibres from the nasal half of the contralateral retina; it forms a compact, somewhat flattened fibre band passing caudolaterally alongside the base of the hypothalamus and over the basal surface of the crus cerebri; most of its fibres terminate in the lateral geniculate body; a smaller number of fibres enter the brachium of the superior colliculus, to terminate in the superior colliculus and the pretectal region. Synonym: tractus opticus. (05 Mar 2000) |
| tectobulbar tract | Fibres originating in the deep layers of the superior colliculus and accompanying the tectospinal tract but, unlike the latter, terminating in medial regions of the pontine and medullary tegmentum. Synonym: tractus tectobulbaris. (05 Mar 2000) |