The systemic circulation is the largest system of arteries and veins in the body. Systemic circulation begins with the aorta – the major artery that travels from left ventricle down the length of the chest and abdomen. About the size of a person’s thumb, the aorta begins by extending upward from the heart. This section is called the ascending aorta. Then it forms a “u,” known as the aortic arch. Smaller arteries branch off from the aortic arch and supply blood to the upper chest area, including the:

From the aortic arch, the aorta travels downward through the chest and abdomen as the descending aorta. The descending aorta, which includes the thoracic aorta (down the length of the chest) and abdominal aorta (down the length of the abdomen), supplies blood to the chest and lower portion of the body. The descending aorta splits off into two smaller iliac arteries that provide blood to the pelvis and lower limbs.

The smaller arteries that branch off from the aorta are like smaller roads branching off from the main highway. These smaller arterial branches carry oxygen-rich blood into the regions furthest from the heart, such as the fingertips, toes and scalp. As the branches continue to narrow (into arterioles), they develop into the smallest blood vessels in the body, capillaries. A capillary is so narrow that red blood cells must pass through it one at a time. There are more than a billion capillaries in the body, with a total surface area of about 1,000 square miles.

Capillaries play a vital role in circulation because they are the sites where the actual exchange of nutrients and waste products takes place at the cellular level. Each red blood cell nourishes the body’s cells with oxygen, water and glucose, and then carries waste products away. The blood (now oxygen-poor and full of waste products) travels from the capillaries into the venules and then into larger veins, such as the saphenous veins in the legs and hips.

Veins in the lower part of the body connect with the inferior vena cava, and veins in the upper part of the body connect with the superior vena cava. Both of these venae cavae empty into the upper-right chamber (right atrium) of the heart, thus completing the systemic circulation.