Ascending aorta

Overview
The ascending aorta is about 5 cm. in length. It commences at the upper part of the base of the left ventricle, on a level with the lower border of the third costal cartilage behind the left half of the sternum; it passes obliquely upward, forward, and to the right, in the direction of the heart’s axis, as high as the upper border of the second right costal cartilage, describing a slight curve in its course, and being situated, about 6 cm. behind the posterior surface of the sternum.

At its origin it presents, opposite the segments of the aortic valve, three small dilatations called the aortic sinuses.

At the union of the ascending aorta with the aortic arch the caliber of the vessel is increased, owing to a bulging of its right wall.

This dilatation is termed the bulb of the aorta, and on transverse section presents a somewhat oval figure.

The ascending aorta is contained within the pericardium, and is enclosed in a tube of the serous pericardium, common to it and the pulmonary artery.

Relations
The ascending aorta is covered at its commencement by the trunk of the pulmonary artery and the right auricula, and, higher up, is separated from the sternum by the pericardium, the right pleura, the anterior margin of the right lung, some loose areolar tissue, and the remains of the thymus; posteriorly, it rests upon the left atrium and right pulmonary artery.

On the right side, it is in relation with the superior vena cava and right atrium, the former lying partly behind it; on the left side, with the pulmonary artery.

Branches
The only branches of the ascending aorta are the two coronary arteries which supply the heart; they arise near the commencement of the aorta immediately above the attached margins of the semilunar valves.