| excision repair | <molecular biology> Mechanism for the repair of environmental damage to one strand of DNA (loss of purines due to thermal fluctuations, formation of pyrimidine dimers by UV irradiation). The site of damage is recognised, excised by an endonuclease, the correct sequence is copied from the complementary strand by a polymerase and the ends of this correct sequence are joined to the rest of the strand by a ligase. The term is sometimes restricted to bacterial systems where the polymerase also acts as endonuclease. (11 Nov 1997) |
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| abdominal aortic aneurysm | <surgery> A distended and weakened area in the wall of the abdominal aorta, more common in those who suffer from atherosclerosis. Symptoms include sudden, severe abdominal pain with radiation to the back. (27 Sep 1997) |
| ampullary aneurysm | A saclike bulging on one side of an artery. Synonym: ampullary aneurysm. (05 Mar 2000) |
| aneurysm | <anatomy, surgery> A sac formed by the dilatation of the wall of an artery, a vein or the heart. The physical signs of arterial aneurysm are the formation of a pulsating tumour and often a bruit (aneurysmal bruit) heard over the swelling. Sometimes there are symptoms from pressure on contiguous parts. Origin: Gr. Aneurysma = a widening (18 Nov 1997) |
| aneurysm by anastomosis | A mass of dilated anastomosing vessels that produce a pulsating tumour usually in a superficial position. (05 Mar 2000) |
| aneurysm, dissecting | Splitting or dissection of an arterial wall by blood entering through an intimal tear or by interstitial haemorrhage. It is most common in the aorta. (12 Dec 1998) |
| aneurysm, false | An aneurysm in which the entire wall is injured and the blood is contained by the surrounding tissues, with eventual formation of a sac communicating with the artery or heart. (12 Dec 1998) |
| aneurysm, infected | Aneurysm due to growth of microorganisms in the arterial wall, or infection arising within preexisting arteriosclerotic aneurysms. (12 Dec 1998) |
| aneurysm of sinus of Valsalva | A congenital thin-walled tubular out pouching usually in the right or non-coronary sinus with an entirely intracardiac course that may rupture into the right or rarely the left heart chambers to form an aortocardiac fistula. (05 Mar 2000) |
| aneurysm, ruptured | The tearing or herniation of the weakened wall of the aneurysmal sac. (12 Dec 1998) |
| aortic aneurysm | Dangeous ballooning of the aorta (the main artery leaving the heart) which is caused by disease in the artery's wall. (09 Oct 1997) |
| aortic aneurysm, abdominal | An aneurysm in that part of the aorta continuing from the thoracic region and giving rise to the inferior phrenic, lumbar, median sacral, mesenteric, renal, and ovarian or testicular arteries. (12 Dec 1998) |
| aortic aneurysm, thoracic | An aneurysm in the proximal portion of the descending aorta proceeding from the arch of the aorta and giving rise to the bronchial, oesophageal, pericardiac, and mediastinal branches. (12 Dec 1998) |
| aortic sinus aneurysm | Abnormal dilation of one or more of the three aortic sinuses situated behind the three aortic valve cusps. (05 Mar 2000) |
| arteriosclerotic aneurysm | The most common type of aneurysm, occurring in the abdominal aorta and other large arteries, primarily in the elderly. Synonym: atherosclerotic aneurysm. (05 Mar 2000) |