| ORD | optical rotatory dispersion; oral radiation death |
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| OROS | oral osmotic |
| ORT | object relations technique; operating room technician; oral rehydration therapy |
| OS | left eye [Lat. oculus sinister]; occipitosacral; occupational safety; office surgery; Omenn syndrome... |
| OSCC | oral squamous cell carcinoma |
| 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) |
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| 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) |
| sigmoid sinus | The S-shaped dural venous sinus lying deep to the mastoid process of the temporal bone and immediately posterior to the petrous temporal bone; it is continuous with the transverse sinus and empties into the internal jugular vein as it passes through the jugular foramen. Synonym: sinus sigmoideus. (05 Mar 2000) |
| sinus | <anatomy> A notch, depression or cavity on the surface of an organ. (09 Oct 1997) |
| sinus alae parvae | A paired dural venous sinus beginning on the parietal bone, running along the sphenoidal ridges and emptying into the cavernous sinus. Synonym: sinus sphenoparietalis, Breschet's sinus, sinus alae parvae. (05 Mar 2000) |
| sinus anales | 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) |
| sinus aortae | The space between the superior aspect of each cusp of the aortic valve and the dilated portion of the wall of the ascending aorta, immediately above each cusp. Synonym: sinus aortae, Petit's sinus, Valsalva's sinus. Arlt's sinus, an inconstant depression on the lower portion of the internal surface of the lacrimal sac. Barber's pilonidal sinus, pilonidal sinus occurring in barbers, usually in the web between the fingers, due to the burying of exogenous hairs by the alternate loosening and tightening of tissues of the hand by the manipulation of scissors. (05 Mar 2000) |
| sinus arrest | <cardiology, physiology> Cessation of sinus activity; the ventricles may continue to beat under ectopic atrial, atrioventricular junctional, or idioventricular control. See: sinus standstill, atrial standstill. (05 Mar 2000) |