| ORT | object relations technique; operating room technician; oral rehydration therapy |
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| OS | left eye [Lat. oculus sinister]; occipitosacral; occupational safety; office surgery; Omenn syndrome... |
| OSCC | oral squamous cell carcinoma |
| OTD | oculotrichodysplasia; oral temperature device; organ tolerance dose |
| OTF | octamer-binding transcription factor; oral transfer factor |
| coccygeal sinus | A fistula opening in the region of the coccyx, being the result of incomplete closure of the caudal end of the neurenteric canal. See: pilonidal sinus. (05 Mar 2000) |
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| pilonidal sinus | A dimple in the crease between the buttocks. (12 Dec 1998) |
| piriform sinus | A recess in the anterolateral wall of the nasopharynx on each side of the vestible of the larynx separated from it by the aryepiglottic folds. Synonym: recessus piriformis, piriform recess, piriform sinus. (05 Mar 2000) |
| Morgagni's sinus | The grooves between the anal columns. Synonym: Morgagni's sinus. Pockets or crypts in the columnar zone of the anal canal between the anocutaneous line and the anorectal line; the sinuses give the mucosa a scalloped appearance. Synonym: sinus anales, anal crypts, Morgagni's crypts, rectal sinuses. (05 Mar 2000) |
| congenital sinus tumour | <radiology> Midline depression or tract, lined with stratified squamous epithelium, most common sites: lumbosacral area, occiput, epidermoid or dermoid cyst anywhere along tract (12 Dec 1998) |
| coronary sinus | A short trunk receiving most of the cardiac veins, beginning at the junction of the great cardiac vein and the oblique vein of the left atrium, running in the posterior part of the coronary sulcus and emptying into the right atrium between the inferior vena cava and the atrioventricular orifice. Synonym: sinus coronarius. (05 Mar 2000) |
| coronary sinus rhythm | An ectopic atrial rhythm supposedly originating from a pacemaker at the mouth of the coronary sinus; recognised in the electrocardiogram by P-waves that are inverted in leads II, III, and a VI with a normal or prolonged P-R interval; an ectopic ("lower") atrial rhythm. (05 Mar 2000) |
| costomediastinal sinus | The recess of the pleural cavity between the costal cartilages and the mediastinum. Synonym: recessus costomediastinalis, costomediastinal sinus. (05 Mar 2000) |
| precervical sinus | In young mammalian embryos a depression in the nuchal region caudal to the hyoid arch, with the third and fourth branchial arches and ectodermal grooves in its floor; normally it is obliterated after the second month, but occasionally cervical fistulae persist as vestiges of it. Synonym: precervical sinus. (05 Mar 2000) |
| prominence of venous valvular sinus | A slight eminence on the external wall of a vein correlating with the valvular sinus immediately proximal to the leaflets of the venous valve. Synonym: agger valvae venae. (05 Mar 2000) |
| prostatic sinus | The groove on either side of the urethral crest in the prostatic part of the urethra into which the prostatic ducts open. Synonym: sinus prostaticus. (05 Mar 2000) |
| Hering's sinus nerve | <anatomy, nerve> A branch of the glossopharyngeal nerve that innervates the baroreceptors in the wall of the carotid sinus and the chemoreceptors in the carotid body. Synonym: ramus sinus carotici, carotid sinus branch, Hering's sinus nerve, intercarotid nerve, nerve to carotid sinus, sinus nerve of Hering. (05 Mar 2000) |
| histiocytosis, sinus | Benign, non-langerhans-cell, histiocytic proliferative disorder that primarily affects the lymph nodes. It is often referred to as sinus histiocytosis with massive lymphadenopathy. (12 Dec 1998) |
| Huguier's sinus | A depression on the medial wall of the middle ear which has the fenestra vestibulae (oval window) in its lower portion. Synonym: Huguier's sinus, little fossa of the vestibular window, little fossa of the vestibular round window. (05 Mar 2000) |
| sick sinus syndrome | <syndrome> A disorder consisting of abnormalities of supraventricular impulse generation and conduction which produce a wide variety of intermittent rapid and slow supraventricular arrhythmias. Common symptoms include palpitations, faintness and fainting. Diagnosis is generally by 24 hour cardiac monitoring. A permanent pacemaker is indicated for those who are unresponsive to drug therapy. (27 Sep 1997) |