| occipital sinus | An unpaired dural venous sinus commencing at the confluence of the sinuses and passing downward in the base of the falx cerebelli to the foramen magnum. Synonym: sinus occipitalis. (05 Mar 2000) |
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| opening of the sphenoidal sinus | One of the pair of openings in the body of the sphenoid bone through which the sphenoid sinuses communicate with the sphenoethmoidal recess of the nasal cavity. Synonym: apertura sinus sphenoidalis, sphenoidal sinus aperture. (05 Mar 2000) |
| tachycardia, sinus | Fast heartbeat (tachycardia) occurring because of rapid firing by the sa node, the natural pacemaker of the heart. Electrical signals initiated in the sa node are transmitted to the atria and the ventricles to stimulate heart muscle contractions heartbeats. Sinus tachycardia is usually a rapid contraction of a normal heart in response to a condition, drug, or disease. For examples, pain, fever, excessive thyroid hormone, exertion, excitement, low blood oxygen level (hypoxia), or stimulant drugs such as caffeine, cocaine, and amphetamines can cause tachycardia. However, in some cases, it can be a sign of heart failure or heart valve disease or other illness. (12 Dec 1998) |
| tentorial sinus | straight sinus |
| terminal sinus | Sinus terminalis, the vein bounding the area vasculosa in the blastoderm. (05 Mar 2000) |
| Tourtual's sinus | The interval between the palatoglossal and palatopharyngeal arches above the tonsil, most obvious after the tonsil has regressed in the adult. Synonym: fossa supratonsillaris, supratonsillar recess, Tourtual's sinus. (05 Mar 2000) |
| endocervical sinus tumour | Malignant germ cell tumour commonly found in the ovary. The tumour arises from primitive germ cells and develops into extra-embryonic tissue resembling the yolk sac. Synonym: yolk sac carcinoma. (05 Mar 2000) |
| endodermal sinus tumour | An unusual and aggressive tumour of germ-cell origin that reproduces the extraembryonic structures of the early embryo. It is the most common malignant germ cell tumour found in children. It is characterised by a labyrinthine glandular pattern of flat epithelial cells and rounded papillary processes with a central capillary (schiller-duval body). The tumour is rarely bilateral. Before the use of combination chemotherapy, the tumour was almost invariably fatal. (12 Dec 1998) |
| Englisch's sinus | A paired dural venous sinus running in the groove on the petrooccipital fissure connecting the cavernous sinus with the superior bulb of the internal jugular vein. Synonym: sinus petrosus inferior, Englisch's sinus. (05 Mar 2000) |
| transverse sinus | A paired dural venous sinus that drains the confluence of sinuses, running along the occipital attachment of the tentorium cerebelli and terminating in the sigmoid sinus. Synonym: sinus transversus, lateral sinus. Transverse pericardial sinus, a passage in the pericardial sac between the origins of the great vessels, i.e., posterior to the intrapericardial portions of the pulmonary trunk and ascending aorta and anterior to the superior vena cava and superior to the atria; it is formed as a result of the flexure of the heart tube, partially approximating the great venous and arterial vessels. Synonym: sinus transversus pericardii, Theile's canal, transverse sinus of pericardium. (05 Mar 2000) |
| transverse sinus of pericardium | transverse pericardial sinus |
| ethmoid sinus | Numerous small thin-walled spaces or air cells in the ethmoid bone, where they form an ethmoidal labyrinth. (12 Dec 1998) |
| tympanic sinus | A depression in the tympanic cavity posterior to the tympanic promontory. Synonym: sinus tympani. Sinus unguis, the deep cleft housing the root of the nail. Synonym: sinus of nail. (05 Mar 2000) |
| unroofed coronary sinus syndrome | <syndrome> A spectrum of cardiac anomalies in which part or all of the common wall between the coronary sinus and the left atrium is absent. (05 Mar 2000) |
| urogenital sinus | The ventral part of the cloaca after its separation from the rectum by the growth of the urorectal septum; from it develops the lower part of the bladder in both sexes, the prostatic portion of the male urethra, and the urethra and vestibule in the female. Synonym: persistent cloaca. (05 Mar 2000) |