The Anatomy of the Aortic Arch

This is the base of the largest blood vessel in the body

The aorta is an artery and is the largest blood vessel in the body. As an artery, the aorta carries blood away from the heart. (Most arteries carry oxygenated blood.) The aorta plays an essential part in supplying oxygenated blood to all of the body except the heart, which gets its blood supply from arteries attached at the very base or root of the aorta.

If it is torn or ruptured during trauma or from a medical condition, the aorta can hemorrhage a potentially fatal amount of the body's total blood volume within minutes. In some cases, the layers of the aorta can begin to separate, leading to a condition called a dissecting aortic aneurysm.

Anatomy of the Aortic Arch

The root of the aorta begins at the left ventricle of the heart and ascends superiorly (goes up toward the head) for about 5 centimeters (about 2 inches) in a section that is called the ascending aorta. There is a one-way valve that allows blood to enter the aorta from the left ventricle during the contraction of the ventricle (called the systole) but prevents blood from flowing backward into the heart when the ventricle rests (diastole). Also at the root is the left and right coronary arteries, which provide circulation to the heart muscle.

At the top of the ascending aorta, the aorta curves downward in an arch and descends inferiorly (toward the feet) until it reaches the diaphragm, the muscle at the floor of the thorax that separates the thorax from the abdomen. This part is called the thoracic descending aorta. The average overall length of the aorta in the thorax—ascending, aortic arch, and descending—is around 33.2 cm or about 13 inches in adult men.

Location of the Aortic Arch

The aortic arch is the part of the aorta between the ascending aorta and thoracic descending aorta. The sharpness of the angle can be different among individuals. The aortic arch gives rise to three arterial branches:

  • Brachiocephalic artery, which supplies blood flow to the right arm and right carotid artery to the right side of the brain
  • Left carotid artery, which provides circulation to the left side of the brain
  • Left subclavian artery, which provides circulation to the left arm

Structure of the Aortic Arch

The only difference between the aorta and other arteries is its size. The overall structure of the aorta is identical to other arteries and subject to the same conditions such as hardening and weakening of the arterial walls. Common to all arterial walls are three main layers:

  1. Tunica intima (tunica interna) is the innermost layer, a simple squamous epithelium-lined with an elastic basement membrane that provides a smooth surface for blood to flow.
  2. Tunica media is the next, thick layer of smooth muscle that provides strength and the ability for the aorta to dilate or contract as necessary.
  3. Tunica adventitia (tunica externa) is the outermost layer of the aorta and connects it to surrounding tissues and structures within the body.

Anatomic Variations of the Aortic Arch

The aortic arch can vary significantly between individuals. The sharpness of the angle of the aortic arch can have an impact on whether the arch is injured when force is applied during blunt trauma. The aorta is larger in men than in women.

Function of the Aortic Arch

The aorta carries blood to the entire body other than the coronary arteries, which provide blood to the heart. One could even say that the coronary arteries also get their blood from the aorta, since those arteries branch off from the root of the aorta.

The aortic arch functions as a manifold to fill the three arteries that branch off of it and to continue the remainder of the blood flow lower on the body.

The muscle tone of the aorta plays a big part in the ability of the heart to fully expand and in the overall control of blood pressure in the body. It also helps create back pressure on blood ejected from the ventricles during systole, which pushes blood into the coronary arteries to provide circulation to the heart muscle.

Clinical Significance

The shape of the aortic arch creates some resistance to blood flow. In some people, the angle of the aortic arch coupled with certain medical conditions can lead to aortic dissection where the ascending aorta meets the aortic arch.

Aortic dissection occurs when a tear in the tunica intima allows blood to be pushed between the tunica intima and the tunica media. The build-up of blood causes a separation of the two layers and a bulge is created on the side of the aorta.

Males over the age of 60 have the highest risk as a group for aortic dissection. People with lifestyles that include episodes of intense strain or stress—such as power weightlifting or the use of cocaine—also have an increased risk of aortic dissection. Other conditions and risk factors of aortic dissection include:

  • High blood pressure
  • Bicuspid aortic valve
  • Arteriosclerosis (hardening of the arteries)
  • Weakening of the aortic wall (aneurysm)
  • Narrowing of the aorta that restricts blood flow (aortic stenosis or coarctation)

Marfan syndrome and Turner's syndrome are two uncommon genetic conditions that can lead to an increased risk of aortic dissection. Turner's syndrome may cause coarctation of the aorta or malformation of the aortic valve. Marfan syndrome can cause aortic aneurysm due to the weakening of connective tissues, including those that make up the arteries.

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