Superior and Inferior Venae Cavae

Venae cavae are the two largest veins in the body. These blood vessels carry oxygen-depleted blood from various regions of the body to the right atrium of the heart. The superior vena cava delivers blood from the head and chest area to the heart, while the inferior vena cava returns blood from the lower body regions to the heart.

As blood is circulated along pulmonary and systemic circuits, oxygen-depleted blood returning to the heart is pump to the lungs by way of the pulmonary artery. After picking up oxygen in the lungs, the blood is returned to the heart and is pumped out to the rest of the body via the aorta. The oxygen-rich blood is transported to cells and tissues where it is exchanged for carbon dioxide. The newly oxygen-depleted blood is returned to the heart again via the venae cavae.

Function of the Venae Cavae

Heart and Major Vessels
This image shows the heart and major blood vessels: superior vena cava, inferior vena cava, and aorta. MedicalRF.com/Getty Images

The superior and inferior venae cavae play a vital role in blood circulation as they return oxygen-poor blood to the heart for re-oxygenation and recirculation.

  • Superior Vena Cava: This large vein brings de-oxygenated blood from the head, neck, arm and chest regions of the body to the right atrium.
     
  • Inferior Vena Cava: This vein brings de-oxygenated blood from the lower body regions (legs, back, abdomen and pelvis) to the right atrium.

Superior Vena Cava
The superior vena cava is located in the upper chest region and is formed by the joining of the brachiocephalic veins. These veins drain blood from the upper body regions including the head, neck, and chest. It is bordered by heart structures such as the aorta and pulmonary artery.

Inferior Vena Cava
The inferior vena cava is formed by the joining of the common iliac veins which meet a little below the small of the back. The inferior vena cava travels along the spine, parallel to the aorta, and transports blood from the lower extremities of the body to the posterior region of the right atrium.

Venae Cavae Anatomy

The structure of the vein wall
MedicalRF.com / Getty Images

Like arteries and medium-sized veins, the walls of the superior and inferior venae cavae are composed of three layers of tissue. The outer layer is the tunica adventitia or tunica externa. It is composed of collagen and elastic fiber connective tissues. This layer allows the vena cava to be strong and flexible. The middle layer is composed of smooth muscle and is called the tunica media. Smooth muscle in this layer allows the venae cavae to receive input from the nervous system. The inner layer is the tunica initima. This layer has an endothelium lining which secretes molecules that prevent platelets from clumping together and helps blood to move smoothly.

Veins in the legs and arms also have valves in the innermost layer that are formed from the infolding of the tunica intima. The valves are similar in function to heart valves, which prevent blood from flowing backwards. Blood within veins flows under low pressure and often against gravity. Blood is forced through the valves and toward the heart when skeletal muscles in the arms and legs contract. This blood is eventually returned to the heart by the superior and inferior venae cavae.

Venae Cavae Problems

Balloon Angioplasty Inferior Vena Cava
This image shows the inferior vena cava being repaired using a balloon angioplasty. The vein has narrowed and weakened due to blood clots. ZEPHYR/Science Photo Library/Getty Images

Due to the important role that the superior and inferior venae cavae play in circulation, problems arising with these large veins can have serious consequences. Since veins have relatively thin walls and the venous system is a low pressure system, both venae cavae are subject to compression by surrounding tissues that swell. This compression inhibits blood flow and impacts proper heart function. The development of blood clots within the venae cavae can also impede or block blood return to the heart.

Superior vena cava syndrome is a serious condition that arises from the constriction or obstruction of this vein. The superior vena cava may become constricted due to enlargement of surrounding tissue or vessels such as the thyroid, thymus, aorta, lymph nodes, and cancerous tissue in the area of the chest and lungs. The swelling may slow or obstruct blood flow to the heart. Superior vena cava syndrome is most often caused by lung cancer and lymphoma.

Inferior vena cava syndrome is caused by the obstruction or compression of the inferior vena cava. This condition results most often from tumors, deep vein thrombosis, congestive heart failure, kidney disease, and pregnancy.

Sources:

"Obstruction of the Veins to the Heart (Superior Vena Cava Syndrome)." UNM Comprehensive Cancer Center, cancer.unm.edu/cancer/cancer-info/cancer-treatment/side-effects-of-cancer-treatment/less-common-side-effects/bloodflow-problems/obstruction-of-the-veins-to-the-heart-superior-vena-cava-syndrome/.

Tucker, William D. "Anatomy, Inferior Vena Cava." National Center for Biotechnology Information, U.S. National Library of Medicine, 18 Feb. 2018, www.ncbi.nlm.nih.gov/books/NBK482353/.