Aorta is the largest artery in the body, carrying blood away from the heart into the systemic arterial tree, the branching arteries that supply the body. It begins at the left ventricle, the heart chamber that pumps blood into the systemic circulation, and passes through the chest and abdomen before dividing into arteries supplying the pelvis and lower limbs.
Where is the aorta located?
The aorta begins at the aortic valve, which controls blood leaving the left ventricle. Its initial portion lies within the pericardium, the sac surrounding the heart, and rises behind the sternum, or breastbone. The pulmonary trunk, the vessel carrying blood from the right ventricle towards the lungs, lies initially in front of it.
The vessel then curves backwards and to the left over the root of the left lung, where the main airway enters and blood vessels and nerves pass into or out of the lung. It continues down the posterior mediastinum, the back part of the central compartment between the lungs, alongside the vertebral column. The oesophagus, the tube connecting the throat to the stomach, lies in front of the lower part of this chest segment.
After crossing the diaphragm, the muscle separating the chest from the abdomen, the aorta lies behind the abdominal cavity lining. This position is called retroperitoneal. It runs in front of the lumbar vertebrae, the spinal bones of the lower back, slightly to the left of the midline and behind the pancreas.
What are the main parts of the aorta?
The thoracic aorta is the portion within the thorax, or chest. In a broad regional description, it includes the initial rising segment, the curved segment and the descending chest segment. The descending portion continues into the abdomen.
| Part | Course and main anatomical feature |
|---|---|
| Ascending aorta | Rises from the left ventricle within the pericardium; gives rise to the coronary arteries. |
| Arch of aorta | Curves backwards and leftwards above the heart; gives rise to the main arteries supplying the head, neck and upper limbs. |
| Descending aorta | Continues from the arch towards the pelvis; includes chest and abdominal portions. |
| Descending thoracic aorta | Runs through the posterior mediastinum and supplies structures in the chest. |
| Abdominal aorta | Extends from the diaphragm to its terminal division and supplies abdominal structures. |
The diaphragm has an opening called the aortic hiatus through which the aorta passes. This lies at the level of the twelfth thoracic vertebra. The aortic bifurcation, the division into the right and left common iliac arteries, usually lies at the level of the fourth lumbar vertebra.
Which arteries branch from the aorta?
Different regions give rise to branches for different territories. The main branching pattern is:
- The right and left coronary arteries arise near the beginning of the ascending aorta and supply the heart muscle.
- The arch of aorta usually gives rise to the brachiocephalic trunk, left common carotid artery and left subclavian artery. The brachiocephalic trunk divides into the right common carotid and right subclavian arteries; together, these vessels supply the head, neck and upper limbs.
- The descending thoracic aorta gives branches to the chest wall, airways and oesophagus, among other structures. Posterior intercostal arteries run between the ribs.
- The abdominal aorta gives rise to the coeliac trunk and superior and inferior mesenteric arteries, which supply abdominal digestive organs. Renal arteries supply the kidneys, while other branches supply the abdominal wall and additional organs.
- The common iliac arteries continue the arterial supply towards the pelvis and lower limbs.
How is the aortic wall structured?
The aorta is an elastic artery, meaning its wall contains abundant elastic tissue that stretches and recoils. Its wall has distinct layers:
- Tunica intima: the inner lining, including the endothelium, a thin sheet of cells in contact with blood.
- Tunica media: the middle layer, containing elastic sheets and smooth muscle, muscle that works without conscious control.
- Tunica adventitia: the outer supporting layer of connective tissue, which binds and supports structures.
The lumen is the space inside the vessel through which blood flows. Near the aortic valve, the wall expands into aortic sinuses, pockets behind the valve leaflets. The coronary arteries arise from the right and left aortic sinuses.
What does the aorta do?
The aorta distributes oxygenated blood from the heart to the body, including the heart itself through the coronary arteries. Its branches progressively divide into smaller arteries that reach organs and tissues.
During systole, the phase when the ventricles contract, blood entering the aorta stretches its elastic wall. During diastole, the phase when the ventricles relax, the wall recoils and helps sustain forward blood flow. The aortic valve prevents blood returning to the left ventricle.
What supplies the aortic wall?
Small vessels called vasa vasorum supply the outer regions of the aortic wall. The inner wall receives oxygen and nutrients by diffusion, movement from the blood within the lumen into nearby tissue.
Autonomic nerves, which regulate involuntary activity, supply the vessel wall, particularly its smooth muscle. Lymphatic vessels drain tissue fluid from the wall towards nearby lymph nodes in the chest and abdomen.
How can you follow the aorta in the 3D model?
In the 3D model next to this article, select the aorta and rotate the model to follow its course from the heart towards the pelvis. Zoom near the arch, then follow the descending portion towards the diaphragm. You can fade or hide neighbouring structures, switch layers on and off, or isolate the aorta to examine its overall course without surrounding structures obscuring it.