Venae Cavae

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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

What Are 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. 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.

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.

Function of the Venae Cavae

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

Venae Cavae Anatomy

The walls of the venae cavae and medium veins are composed of three layers of tissue. The outer layer is the tunica adventitia. 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. 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

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 obstructs blood flow to the heart. 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, and pregnancy.