The Anatomy of the Ascending Aorta

The beginning of the biggest blood vessel in the body

In This Article

Table of Contents

The ascending aorta is the first part of the aorta originating at the left ventricle and leading into the aortic arch. The aorta is the largest blood vessel in the body. It is an artery that carries blood directly from the heart and provides circulation for nearly all of the body's tissues. The ascending aorta is only 5 centimeters (cm) long, but it is a very important segment of the aorta and can become dilated or develop an aneurysm. Fifty percent of thoracic aortic aneurysms develop in the ascending aorta.

The significance of the aorta and the implications of aortic aneurysm have been known since long before the birth of Christ. The first relatively successful surgical treatment for aortic aneurysms wasn't developed until the late 1800's and only became dependable in the second half of the 20th Century.

Anatomy

The ascending aorta is about 5 cm long depending on the size, age, and sex of the person. It originates at the aortic valve, also known as the tricuspid valve, in most patients. Approximately 1% of the population has a different type of aortic valve. The valve only allows blood to flow in one direction, out of the left ventricle chamber of the heart and into the aorta.

Location

The left ventricle sits high on the left side of the heart and the aortic valve is right on top. This places the aortic root and the ascending aorta at the pinnacle of the heart in the most superior position. It ascends directly superior from there.

The entire ascending aorta is located in the chest cavity known as the mediastinum.

Structure

The ascending aorta is divided into two segments: the aortic root and the tubular segment of the ascending aorta.

The aortic root is where the aorta meets the aortic valve. It is comprised of a combination of muscle from the left ventricle and typical arterial structure. It's hard to discern where one ends and the other begins. Technically, the valve is not part of the aorta, but the three leaflets of the valve extend all the way into the aortic root and they work in tandem to control blood flow and to backfill the coronary arteries.

There are three sinuses in the aortic root (sinuses are like depressions in the wall) known as the Sinuses of Valsalva. Two of the sinuses lead to the origins of the left and right coronary arteries, which provide the cardiac muscle with blood. The third sinus in the aortic root is not connected with an artery.

The three sinuses correspond with the three leaflets of a normal aortic valve. The sinuses are thought to provide back pressure to help close the valve and fill the coronary arteries.

Superior to (above) the aortic root is the tubular segment of the ascending aorta. This portion is about 2 to 3 cm and rises away from the root until it reaches the brachiocephalic artery, which marks the beginning of the aortic arch. The point where the aortic root and the tubular ascending aorta meet is called the sinotubular junction.

The structure of the aortic walls is identical to other arteries. Common to all arterial walls are three main layers:

  1. Tunica intima (tunica interna) is the innermost layer, an elastic membrane that provides a smooth surface for blood to flow.
  2. Tunica media comes next, a thick layer of smooth muscle that gives the aorta the ability to dilate or contract as necessary.
  3. Tunica adventitia (tunica externa) is the outermost layer and connects the aorta to surrounding tissues and structures.

Anatomical Variations

The most common variations of the ascending aorta are the overall circumference and the presence of a bicuspid aortic valve instead of a tricuspid aortic valve. While the valve leaflets are not technically part of the aorta, the development of the aortic root is related to the structure of the valve. As much as 1% of the population is believed to have a bicuspid aortic valve (BAV).

The circumference of the ascending aorta is significant clinically and might be a precursor to an aneurysm. However, the size of the ascending aorta varies based on the size, age, and sex of the person. Doctors are encouraged to consider the size and age of the patient when deciding whether an ascending aorta is dilated or of a normal circumference.

Function

The aorta supplies oxygenated blood to nearly all of the body's tissues. Its ability to dilated and constrict, like all arteries, plays a major role in regulating blood pressure throughout the cardiovascular system.

The ascending aorta provides a low-resistance pathway for blood flow being ejected out of the left ventricle when it contracts and squeezes blood through the aortic valve. The surge of blood flow creates a pressure wave that resonates through the entire cardiovascular system and is what causes a pulse to be felt in certain areas of the body.

The constriction of the left ventricle is known as systole. After contracting, the ventricle relaxes and it is known as diastole. The relaxation and subsequent dilation of the ventricle pull blood into it. The backflow of blood forces the three leaflets of the aortic valve to snap closed and prevent blood from flowing back into the ventricle.

While doctors aren't completely sure, it is thought that the sinuses in the aortic root create a swirling motion of blood to begin pushing the leaflets of the aortic valve closed even before diastole creates backward pressure. The sinuses might also simply keep the leaflets of the aortic valve from getting plastered flat along the walls of the aortic root, sticking them in the open position. Either way, when surgeons leave the sinuses in place during repairs of the aortic root, the valve functions better.

Clinical Significance

For such a small portion of the largest blood vessel, the ascending aorta has more than its share of issues. The aortic root and the ascending aorta are ground zero for many clinical procedures, including cannulization of the coronary arteries, repairs of the aortic valve, and surgical repair of thoracic aortic aneurysms. Aortic stenosis and aortic aneurysm are the two most common conditions that can affect the ascending aorta.

Thoracic Aortic Aneurysm

The most concerning condition that can affect the ascending aorta is an aortic aneurysm. This is a localized dilation of the aorta—basically, a bulge.

Aortic aneurysms are significant no matter where they are located. Thoracic aortic aneurysms can occur anywhere above the diaphragm, but about half of all thoracic aortic aneurysms show up in the ascending aorta.

An aortic aneurysm can cause a separation between the layers of the aortic wall in what's known as a dissecting aortic aneurysm.

A dissecting aortic aneurysm is a potentially life-threatening condition and true medical emergency almost always requiring surgery to repair. Symptoms vary between patients, but the most common are pain, lightheadedness, syncope (AKA fainting), and fatigue.

The pain of a dissecting aneurysm in the ascending aorta is usually described as severe sharp chest pain that comes on suddenly. It can also be back pain.

Treatment for an aortic aneurysm depends greatly on whether the aneurysm is dissecting or not. Regardless, initial treatment focuses on controlling the pressure affecting the area of the aorta where the aneurysm is located.

If needed, a thoracic surgeon will have to repair the aneurysm using a variety of techniques that depend on the location and severity of the aneurysm. In some cases, the aortic root may be rebuilt or replaced.

Aortic Stenosis

Narrowing of the opening to the aortic root around the aortic valve is called aortic stenosis and is not completely understood. It was believed to be a calcification of the aortic valve from "wear and tear" but now is recognized as a much more complicated etiology that includes lipids, inflammation, and calcification.

Symptoms of aortic stenosis include cardiac-related chest pain, syncope, lightheadedness, and shortness of breath, especially when active.

Treatment for aortic stenosis includes prevention through diet, exercise, and controlling hypertension. Repair is usually surgical and can take a variety of forms.

Genetic Significance

Bicuspid aortic valve (BAV) is the most common congenital malformation of the heart. It appears in up to 1% of the general population and between 40% to 50% of those people develop dilated ascending aorta or dilation of the aortic root.

Thoracic aortic aneurysm associated with a bicuspid aortic valve is the most common type of thoracic aortic aneurysm in humans.

Marfan syndrome: One of the most well-known genetic causes of dissecting aortic aneurysm is associated with Marfan syndrome, a genetic condition of the connective tissue that results in joint problems and various heart conditions. The connection between Marfan syndrome and thoracic aortic aneurysms is so well-documented that some of the evidence and reviews do not include patients without Marfan syndrome.

Loeys-Dietz syndrome: Loeys-Dietz syndrome is another genetic connective tissue disease that was only recently identified. Its primary association is with thoracic aortic aneurysms.

Was this page helpful?

Article Sources

  1. Cooley DA. A Brief History of Aortic Aneurysm SurgeryAorta (Stamford). 2013;1(1):1–3. doi:10.12945/j.aorta.2013.12.006

  2. Saliba E, Sia Y. The ascending aortic aneurysm: When to intervene? Int J Cardiol Heart Vasc. 2015;6:91–100. doi:10.1016/j.ijcha.2015.01.009

  3. Isselbacher EM, Lino Cardenas CL, Lindsay ME. Hereditary Influence in Thoracic Aortic Aneurysm and Dissection. Circulation. 2016;133(24):2516–2528. doi:10.1161/CIRCULATIONAHA.116.009762

  4. Charitos EI, Sievers HH. Anatomy of the aortic root: implications for valve-sparing surgery. Ann Cardiothorac Surg. 2013;2(1):53–56. doi:10.3978/j.issn.2225-319X.2012.11.18

  5. Hiratzka LF, Bakris GL, Beckman JA, et al. 2010 ACCF/AHA/AATS/ACR/ASA/SCA/SCAI/SIR/STS/SVM Guidelines for the diagnosis and management of patients with thoracic aortic disease. J Am Coll Cardiol. 2010 Apr 6;55(14):e27-e129. doi:10.1016/j.jacc.2010.02.015

  6. Pawade TA, Newby DE, Dweck MR. Calcification in Aortic Stenosis: The Skeleton Key. J Am Coll Cardiol. 2015 Aug 4;66(5):561-77. doi:10.1016/j.jacc.2015.05.066