Great Vessels in the Thorax

The Large Arteries of the Thorax

  1. The Aorta

  • The thoracic aorta is conventionally divided into ascending, arch, and descending parts. The short ascending aorta leaves the left ventricle and runs upwards and forwards to the level of the sternal angle. Its only branches are the left and right coronary arteries.

  • The arch of the aorta lies behind the manubrium sterni and runs upwards, backwards, and to the left, in front of the trachea, then turns downwards and to the left, behind the left main bronchus. The brachiocephalic artery leaves the ascending part of the aortic arch and runs upwards to the right of the trachea where it divides behind the right sternoclavicular joint into the right subclavian and right common carotid arteries supplying the arm and head, respectively. On the left side, the common carotid and subclavian arteries arise separately from the upper surface of the arch; the left common carotid artery runs along the left side of the trachea to the neck and the left subclavian artery runs deep to the common carotid. Each subclavian artery gives off important branches that supply structures in the head and neck, including the brain.

  • The descending (thoracic) aorta runs downwards from the aortic arch and leaves the thorax through the aortic opening behind the diaphragm where it becomes the abdominal aorta. The descending aorta has many branches in the thorax. Pairs of posterior intercostal arteries supply the contents of the intercostal spaces, and the subcostal arteries which run below the twelfth ribs. Pairs pericardial, esophageal, and bronchial branches supply the corresponding structures.

    2. The Pulmonary Trunk

  • The pulmonary trunk leaves the right ventricle and runs upwards, backwards, and to the left. It divides into the left and right pulmonary arteries, close to the concavity of the arch of the aorta. The right pulmonary artery runs behind the ascending aorta and superior vena cava to the root of the right lung. The left pulmonary artery runs in front of the descending aorta to the root of the left lung.

  • The fibrous ligamentum arteriosum runs between the bifurcation of the pulmonary trunk and the concave side of the aortic arch. It is a remnant of an embryonic structure in the circulatory system. The left recurrent laryngeal nerve loops around the lower border of the arch of the aorta behind the ligamentum.

The Large Veins of the Thorax

The right and left brachiocephalic veins are formed at the root of the neck by the union of the subclavian and internal jugular veins of the same side just above the first rib. The brachiocephaalic veins pass down behind the manubrium sterni and superficial to the large branches of the aorta to unite to form the superior vena cava a little above the level of the sternal angle. The left brachiocephalic vein is longer and runs more horizontally than the right vein. The superior vena cava passes downwards to the right atrium.

The inferior vena cava, draining venous blood from the body below the diaphragm, pierces the diaphragm and empties into the right atrium almost immediately.

Two pulmonary veins leave each lung and drain oxygenated blood into the left atrium. The veins draining the thoracic cavity are a complex of unpaired azygos veins.

Arteries of the Thorax

  1. Internal thoracic artery - a branch of the subclavian artery that descends just lateral to the sternum and terminates at the intercostal space 6 by dividing into the superior epigastric artery and musculophrenic artery. The superior epigastric artery continues inferiorly into the anterior abdominal wall while the musculophrenic artery passes along the costal margin, goes through the diaphragm, and ends near the last intercostal space. This artery also provides collateral circulation to the abdomen in the event of a blockage of the descending aorta.

  2. Anterior intercostal artery - supplying intercostal spaces 1-6 are branches of the internal thoracic artery, supplying intercostal spaces 7-9 are branches of the musculophrenic artery. There are two anterior intercostal arteries within each intercostal space that anastomose with the posterior intercostal arteries.

  3. Posterior intercostal arteries - supplying intercostal spaces 1 and 2 are branches of the superior intercostal artery that arises from the costocervical trunk of the subclavian artery . Supplying intercostal spaces 3-11 are branches of the thoracic aorta. All posterior intercostal arteries give off a posterior branch, which travels with the dorsal primary ramus of a spinal nerve to supply the spinal cord, vertebral column, back muscles and skin. The posterior intercostal arteries anastomose anteriorly with the anterior intercostal arteries.

Veins of the Thorax

  1. Anterior intercostal veins - these drain the anterior thorax and empty into the internal thoracic veins, which then empty into the brachiopcephalic veins.

  2. Posterior intercostal veins - these drain the lateral and posterior thorax and empty into the hemiazygos veins on the left side and the azygos vein on the right side. The hemizaygos veins empty into the azygos vein, which empties into the superior vena cava.