The Anatomy of the Aorta

The aorta is the largest artery in the body. It carries oxygen-filled blood from the heart to different organs in the body. The aorta starts at the heart’s left ventricle, arches upwards towards the neck, then curves back downward, extending into the abdomen. Learn more about the important role the aorta plays in the body.

Anatomy

Structure

The aorta is the largest artery in the body to which all other major arteries are connected. It is a big tube-like structure, usually about 1 inch wide in diameter, although its size varies proportionally to the height and weight of the person. The aorta is widest at the point where it connects to the heart's left ventricle through the aortic valve; then, it gets progressively narrower as it descends into the abdomen.

The aorta is divided into four parts:

• Ascending aorta: This is the first part of the aorta and it is connected to the left ventricle of the heart (the part that pumps oxygenated blood to the body's tissues and organs). The ascending aorta starts at the aortic valve which closes and opens to stop and allow the flow of blood from the heart into the aorta.
• Aortic arch: This is the part of the aorta that curves upward toward the head and neck. It starts where the ascending aorta ends.
• Descending aorta: This is the part of the aorta that travels downward from the aortic arch through the chest. It is also known as descending thoracic aorta or simply thoracic aorta.
• Abdominal aorta: This is the final part of the aorta. It starts at your diaphragm and ends where the aorta splits off into the two arteries (iliac arteries) that extend into the legs.

The aorta also has three layers in its wall. The tunica intima is the inner layer. This layer is a smooth surface where the blood flows on. It is thin and made of endothelial cells and supporting tissue.

The tunica media is the middle layer. This layer is made of smooth muscle, elastic tissue, and collagen. The tunica adventitia is the outer layer. This layer is made of connective tissue like collagen and a network of small blood vessels (known as vasa vasorum) whose function is to nourish the aorta.

Location

The aorta is located at different parts of the body. It starts at the heart’s left ventricle, goes through the chest, and ends at the lower abdomen.

Anatomical Variations

For people that have dextrocardia (a condition where the heart is located on the right side of the body), the aorta is usually on the right side instead of on the left side. The same applies to people who have a condition called situs invertus, where all the organs are on the opposite side of where they usually are—like a mirror image.

There is a birth defect known as coarctation of the aorta, in which a part of the aorta is significantly narrower than it ordinarily should be. The narrowing is usually found right after the arteries that supply blood to the head and arms have arisen from the aorta. This narrowing occurs when the baby's aorta doesn't form properly while it's in the womb and its effect is that it doesn’t let blood flow to the body properly. This variation causes high blood pressure and eventual heart damage if it’s not corrected.

There is a common birth defect where babies are born with what is known as a bicuspid aortic valve. Usually, the aortic valve has three leaflets or "cups" through which blood passes into the aorta. With a bicuspid aortic valve, there are only two. This condition is often found in babies born with coarctation of the aorta, too. A bicuspid aortic valve can lead to conditions like aortic stenosis and aortic regurgitation later in adulthood if it’s not surgically corrected.

Function

The main function of the aorta is to supply blood to almost all the major organs in the body through the smaller arteries that arise from it.

Broken down, the function of the different parts of the aorta are:

• Ascending aorta: This part of the aorta connects to the aortic valve and it collects oxygenated blood from the left ventricle of the heart. It also gives rise to the left and right coronary arteries which supply blood to the heart.
• Aortic arch: This part gives rise to the right common carotid artery and the right subclavian artery (protruding from the brachiocephalic trunk) which supply blood to the right side of the head and neck and the right arm respectively. The left common carotid artery and the left subclavian artery which supply blood to the left side of the head and neck and the left arm respectively also branch off from the aortic arch.
• Descending aorta: This part has many smaller arteries branching out from it that supply blood to the esophagus, pericardium, the top part of the diaphragm, lymph nodes, ribs, and some other structures in the chest.
• Abdominal aorta: This final part of the aorta gives rise to the largest number of arteries. The arteries branching out from it supply the liver, diaphragm, stomach, spleen, abdominal esophagus, intestines, kidneys, spinal cord, and pancreas. It also gives rise to the iliac arteries which then supply the legs, gluteal muscles, and the organs in the pelvic area.

Clinical Significance

There are several conditions with serious complications that center around or affect the aorta.

Aortic aneurysm: An aortic aneurysm is a weakened point on the aorta. It occurs when the aorta is not able to contract and expand to accommodate the passage of blood properly. It is a serious condition because if the aorta ruptures at that spot, it can lead to severe internal bleeding and other serious complications.

Aortic atherosclerosis: This is when plaque (made up of substances like cholesterol and calcium) collects and hardens inside the aorta blocking the free flow of blood through it and weakening the aortic walls. It can lead to aortic aneurysms, arterial thrombosis, strokes, and anginas.

Aortic dissection: This is when blood flows between the inner and middle layers of the aortic wall through a tear in the inner layer. This causes the layers to separate (dissect). It is typically caused by atherosclerosis, hypertension, connective tissue disorders, and injuries. It is a very dangerous condition and can lead to aortic regurgitation, gastrointestinal bleeding, myocardial infarction, kidney failure, and pericardial effusion.

Penetrating Aortic Ulcer: This is a chronic condition that’s very similar to aortic dissection but is usually considered a separate condition because the cause of dissection is not a tear in the wall. Instead, the cause is ulcers formed due to wear of the aortic wall which is caused by atherosclerosis.

Aortoenteric Fistula (AEF): This is a rare condition in which an abnormal connection forms between the aorta and the bowel. It usually only occurs in patients who have had surgery to treat an aortic aneurysm in the past. It is a life-threatening condition that is difficult to diagnose. Its complications are infections and gastrointestinal bleeding.

Aortobronchial fistula (ABF): This is another rare condition where an abnormal connection forms between the aorta and the tracheobronchial tree—the structure that supplies air to the lungs. This condition usually occurs in people who have aortic aneurysms or have had a previous surgical graft to treat an aortic condition. Its major complication is hemoptysis, or coughing up blood or mucus mixed with blood.

Aortic stenosis: With this condition, the aortic valve doesn’t open completely when it should, making the heart have to pump harder to get blood through the valve and into the aorta. It can lead to complications like left ventricular hypertrophy (LVH), diastolic dysfunction, and diastolic heart failure.

Aortic regurgitation: This is when the aortic valve doesn't close properly and thus lets the blood flow back into the left ventricle of the heart. Its acute form is caused by infective endocarditis and aortic dissection in the ascending part. The chronic form, which typically doesn't show any symptoms for a long time, is caused by the deterioration of the aortic valve, aneurysm in the thoracic aorta, rheumatic fever, infective endocarditis, and trauma. It can lead to pulmonary edemas, left ventricular hypertrophy (LVH), arrhythmias, and heart failure. It is also known as aortic insufficiency.

Aortitis: This is the inflammation of the aorta. It could be caused by a number of reasons like injury and infection. It can also be caused by conditions like giant cell arteritis and Takayasu arteritis (when the artery they affect is the aorta). Aortitis is rare, but it can lead to serious complications like heart failure and aortic aneurysms.