The aorta is the main artery that conveys blood pumped out of the heart to the body. It is has a complicated shape, initially pointing upwards towards the head for before arching downwards and backwards to the supply the rest of the body. The aortic valve is situated in the first part of the aorta and prevents blood that has been ejected from the heart flowing back into the heart.
Anatomy of the thoracic aorta
The thoracic aorta begins at the left ventricle of the heart and ends when the descending aorta passes through the diaphragm and becomes the abdominal aorta.
The thoracic aorta can be divided in to four distinct parts.
- The aortic root
- The ascending aorta
- The aortic arch
- The descending aorta
Although the thoracic aorta is described in distinct parts, there is no interruption between these parts. These distinctions are important as they allow surgeons to determine what procedures will be required to fix problems that have been detected.
The aortic root
The aortic root begins arises from the left ventricle of the heart and finishes at an area called the sinotubular junction. The aortic root includes several structures – the aortic annulus, the aortic valve and the sinuses of Valsalva from which the coronary arteries, which supply blood to the muscle of the heart, arise.
The ascending aorta
The ascending aorta begins at the sinotubular junction and extends to the point at which the first of the major branches of the aorta, the brachiocephalic artery (otherwise known as the innominate artery), arises. The brachiocephalic artery supplies blood to the head and neck (as well as other structures). The ascending aorta has no branches arising from it.
The aortic arch
The position of the aorta changes significantly during the course of the aortic arch. The aorta begins in the center of the chest and directs blood upwards towards the head. At the end of the aortic arch the aorta is positioned at the back of the chest to the left of center and the flow of blood is directed downward towards the feet. The aortic arch has several important branches that supply both arms, the head and the neck. These branches are the brachiocephalic (or innominate) artery, the left common carotid artery and the left subclavian artery. The aortic arch begins at the origin of the brachiocephalic artery; it ends at the origin of the left subclavian artery.
The descending aorta
The descending aorta begins after the origin of the left subclavian artery and descends until the thoracic aorta passes through the diaphragm. The diaphragm is a sheet of muscle that separates the thoracic cavity from the abdominal cavity. Multiple small arteries that supply the chest wall and lungs arise from the descending aorta.
The wall of the aorta
The wall of the aorta has three main layers these are the tunica intima, the tunica media and the tunica adventitia.
The tunica intima consists of a thin sheet of specialised cells called endothelial cells which provide a smooth surface lining for blood to flow through, they also have an important role in the production of various chemical mediators for blood clotting, the response to infection and injury and the regulation of blood flow.
The tunica media, particularly in the thoracic aorta, is a thick layer containing a large number of elastic and muscular fibers. The tunica adventitia is the outermost layer and is tough coating of connective tissues containing the nerve supply to the vessel as well as tiny blood vessel that supply the wall of the aorta called the vasa vasorum.
An awareness of these layers is important when considering problems that can arise with the thoracic aorta.