There are two veins in the body that are considered the largest ones, and these are the Superior and Inferior Vena Cava. The Superior Vena Cava is in the upper chest, and it forms where the brachiocephalic veins join together. The aorta and pulmonary artery are located near the Superior Vena Cava.
Meanwhile, the Inferior Vena Cava is located below the small of the back and is created by the joining of the common iliac veins. Blood from the lower extremities of the body to the posterior of the right atrium is carried through the Inferior Vena Cava.
Both carry de-oxygenated blood to the right atrium of the heart.
Three layers of tissue make up the outer walls of the venae cavae. The first layer is the tunica adventitia, which contains elastic fiber connecting tissues and collagen. The second layer is the tunica media, which is made of smooth muscle. The third layer is the tunica intima, which helps the blood move smoothly because it secretes molecules and makes sure the platelets in the blood do not clump together.
Blood flows through the valves and to the heart. Various veins in the body, like the veins in the legs and arms, have valves that prevent the blood from flowing backward. This is to help keep the blood flowing in the right direction when it needs to go back to the heart, despite the fact that it flows at low pressure and against gravity.
There are conditions that can impact the venae cavae. These include Superior vena cava syndrome, which occurs when the vein is obstructed or constricted. This can lead to obstruction of blood flow to the heart. It typically occurs because tissue like the thyroid, aorta or lymph nodes enlarge. Cancerous tissue in the lungs or chest can also cause this obstruction. This is the most common cause of this condition, and typically treatment focuses on the cancer or other cause of the constriction in order to resolve the issue at the same time.
There is also a condition called Inferior vena cava syndrome, which occurs when tumors, deep vein thrombosis or a condition like pregnancy causes obstruction or constriction of the blood flow in the inferior vena cava. When this condition is caused by cancer, radiotherapy is used as treatment. For those who have this condition occur due to pregnancy, the situation may be alleviated with changing positions or ultimately — the delivery of the baby.
For pregnant women, compression of the inferior vena cava is relatively common. The issue can be addressed by avoiding rest on their back or right side. For those who continue to experience issues despite the effort to rest on their left side, other methods may be needed to address the problem. In severe cases, the baby is delivered if it is considered a safe alternative. Some women have issues with this syndrome without showing symptoms or otherwise being impaired by the situation. Therefore, it is thought that almost all women may experience this condition at some point during a pregnancy.