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Other Terms: Trunk of aortic tree, Trunk of systemic arterial tree, Aorte
The thoracic aorta is divided into three parts: ascending aorta, aortic arch, and descending aorta. The origin of the aorta at its ventricular attachments shows three little bellies externally: two in front, one on the right and the other on the left side. The fatter is posterior to the pulmonary artery, and a third on the posterior surface. They are called aortic sinuses. These sinuses mark the location of the aortic valves. From the two anterior, right and left, arise the right and left coronary arteries. This portion of the aorta, along with the pulmonary artery, is invested by an extension of the pericardiaI covering of the heart. Anterior to the beginning of the ascending aorta are the pulmonary artery and right auricle. Higher up, the pericardium, connective tissue, the remains of the thymus gland, the right pleura, and the thin margin of the right lung separate it from the sternum. Posterior to it are the right pulmonary artery, the left atrium, and the right deep cardiac nerves. On its right side it sits against the right atrium and the superior vena cava. While on its left side, it is in relation with the pulmonary artery, the left atrium, and the left pleura and lung. The ascending aorta begins at the conus arteriosus of the left ventricle. Here, it is overlapped on its left side by the origin of the pulmonary artery, and on its right side, by the right auricle. It originates opposite the middle of the sternum on a level with the lower border of the third sternochondral junction. The ascending aorta with the pulmonary artery is largely covered by the fibrous layer of the pericardium. The part covered by pericardium is contained in the middle mediastinum; the remainder is located in the superior mediastinum. It is considerably lumpy anteriorly and toward the right, just where its walls receive the direct impact of the column of blood forced out of the powerful left ventricle. This dilated portion is known as the bulb of the aorta. It is the part of the aorta which receives the greatest strain. The ascending aorta passes upward, forward, and to the right, as high as the upper margin of the second right costal cartilage. At this point, it extends slightly beyond the right border of the sternum. Here, it is overlapped by the right pleura and the anterior margin of the right lung. The aortic arch now begins. From this point, the aortic arch passes transversely across the chest cavity and obliquely posterior from right to left to the left side of the fourth thoracic vertebra. These parts, with the exception of the portion of the ascending aorta that is covered by pericardium, are contained in the superior mediastinum. It extends to an inch within of the suprasternal notch. The brachiocephalic, left common carotid, and the left subclavian arteries arise from its upper border. It extends to the left and backwards across the superior mediastinum to end at the left side of the lower border of the fourth dorsal vertebra. It is partly covered by the left pleura and lung and to a lesser extent by the right pleura and lung. It is crossed by the left phrenic nerve, the left vagus nerve and its cardiac branches, the left superior cardiac branch of the cervical sympathetic, and the terminal part of the left superior intercostal vein. Behind it lie the trachea, the deep cardiac plexus, the esophagus, the thoracic duct, and the left recurrent nerve. Above it are its three great branches and the left brachiocephalic vein. Below it, in the concavity of the arch, are the divisions of the pulmonary artery, the remains of the ductus arteriosus, the left recurrent nerve, as it winds around the arch, the superficial cardiac plexus, the left bronchus, and some lymph glands. The descending thoracic aorta, begins at the left lower border of the fourth dorsal vertebra, lies in the posterior mediastinum and is covered anteriorly by the pleura and root of the left lung and pericardium. Posteriorly, it lies against the spine, at first on the left side of the bodies of the vertebrae, and then approaches the median line. On its right side is the esophagus, thoracic duct, and azygos. At the lower portion of the chest, the esophagus is anterior and to the left of the aorta. Its left side is in relation with the pleura. The abdominal aorta is the continuation of the thoracic aorta. It is about twelve centimeters long. It begins at the aortic opening in the diaphragm, opposite the lower border of the body of the twelfth thoracic vertebra. It extends downward upon the left side of the front of the bodies of the lumbar vertebrae to the middle of the body of the fourth lumbar vertebra. Opposite this, it divides into the right and left common iliac arteries. The aorta gives off large branches and thus tapers off rapidly as it descends. It is related, behind, with the four upper lumbar vertebrae and the intervertebral discs, from which it is separated by the anterior longitudinal ligament, the left lumbar veins, the lower end of the thoracic duct, and the origin of the left crus of the diaphragm. In front of it are the liver, the lesser omentum, the stomach, the posterior parietal peritoneum, the pancreas, the transverse duodenum, the celiac trunk and its branches, the celiac plexus, the aortic plexus, the splenic vein, the left renal vein, and the mesentery. On its right side are: the right crus of the diaphragm, the vena azygos, the thoracic duct, the celiac ganglion, the right greater splanchnic nerve, and the inferior vena cava. On its left side are; the left greater splanchnic nerve, the left celiac ganglion, the left crus of the diaphragm, the psoas major muscle, the tail of the pancreas, and the left kidney. The branches of the abdominal aorta are: the inferior phrenic arteries, the celiac trunk, the superior mesenteric, the suprarenal, the renal, the spermatic or ovarian, the inferior mesenteric, the lumbar, and the middle sacral arteries. Its terminal branches are the right and left common iliac arteries.