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The aorta represents a complex organ system which begins in the aortic ring adjacent to the aortic root with the origin of the two major coronary arteries, and ends at the iliac bifurcation. The subdivision into seven segments seems to be clinically important—the aortic root, the ascending aorta, the ascending aortic arch, the vessel bearing arch, the aortic isthmus, and the thoracic descending and abdominal aorta. The aorta as an organ can be regarded as a biological “windkessel”, storing kinetic energy during systole which is delivered during diastole in order to maintain a relative constant mean aortic pressure. In particular, a high diastolic blood pressure is important for the coronary perfusion.
The size of the aorta decreases with distance from the aortic valve in a tapering fashion. The normal diameter of the ascending aorta has been defined as <2.1 cm/m2 and of the descending aorta as <1.6 cm/m2.1 The normal diameter of the abdominal aorta is regarded to be less than 3.0 cm. The normal range has to be corrected for age and sex, as well as daily workload.
The aortic wall consists of three layers: intima, media, and adventitia. The intima is thin, the media contains the elastic fibres and smooth muscle cells forming a spiral layer of tissue providing the strength of the aortic wall, and the adventitia provides the nutrition with the arterial and venous vasa vasorum. An inner vasa vasorum from the aortic lumen also seems to be present.2 A wall thickness of < 4 mm is regarded as normal.
During life the size of the aorta increases. The normal expansion rate is about 1–2 mm/year. It involves all segments which, during childhood and in young adulthood, result in an increase of the luminal diameter of the entire aorta (figs 1 …
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