| orifice of inferior vena cava | The orifice through which the inferior vena cava opens into the right atrium. Synonym: ostium venae cavae inferioris, orifice of inferior vena cava. (05 Mar 2000) |
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| orifice of internal acoustic meatus | The inner opening of the internal acoustic meatus on the posterior surface of the petrous part of the temporal bone. Synonym: porus acusticus internus, internal acoustic foramen, internal acoustic pore, auditory pore, internal auditory foramen, orifice of internal acoustic meatus. (05 Mar 2000) |
| orifice of superior vena cava | The point of entry of the superior vena cava into the right atrium. Synonym: ostium venae cavae superioris, orifice of superior vena cava. (05 Mar 2000) |
| tricuspid orifice | An atrioventricular opening which leads from the right atrium into the right ventricle of the heart. Synonym: ostium atrioventriculare dextrum, ostium venosum cordis. (05 Mar 2000) |
| external urethral orifice | The slitlike opening of the urethra in the glans penis, the external orifice of the urethra (in the female) in the vestibule, usually upon a slight elevation, the papilla urethrae. Synonym: ostium urethrae externum, external opening of urethra, meatus urinarius, orificium urethrae externum. (05 Mar 2000) |
| ureteric orifice | The opening of the ureter in the bladder, situated one at each lateral angle of the trigone; wide gaping of the ostium usually indicates vesicoureteral reflux. Synonym: ostium ureteris, orificium ureteris, ureteral meatus, ureteral opening. (05 Mar 2000) |
| arrhythmias, atrial | Abnormal heart rhythm due to electrical disturbances in the atria (the upper chambers of the heart) or the AV node relay station , leading to fast heart beats. Examples of atrial arrhythmias includes atrial fibrillation, atrial flutter, and paroxysmal atrial tachycardia (PAT). (12 Dec 1998) |
| atrial | <anatomy> Pertaining to an atrium. (16 Dec 1997) |
| atrial appendage | The small projection from each atrium hanging over like a small ear, more marked on the left, with a small cavity of its own. (05 Mar 2000) |
| atrial arrhythmias | See Arrhythmias, atrial. (12 Dec 1998) |
| atrial arteries | Branches of the right and left coronary arteries distributed to the muscle of the atria. Synonym: arteriae atriales. (05 Mar 2000) |
| atrial auricle | The auricle of atrium. See: left atrium, right atrium. (05 Mar 2000) |
| atrial auricula | A small conical ("ear-shaped") pouch projecting from the upper anterior portion of each atrium of the heart, increasing slightly the atrial volume. See: auricle of left atrium, auricle of right atrium. Synonym: auricula atrialis, atrial auricle, atrial auricula, auricle, auricula, auricular appendage, auricular appendix, skin tag. (05 Mar 2000) |
| atrial bigeminy | Pairing of atrial beats, as when an atrial extrasystole is coupled to each sinus beat. (05 Mar 2000) |
| atrial branches | The atrial branches, the branches of the right coronary artery and the circumflex branch of the left coronary artery distributed to the right and left atrium, respectively. Synonym: rami atriales. (05 Mar 2000) |