Vein

From ArticleWorld

A vein, as it applies to biology and anatomy, is a thin-walled blood vessel that carries blood, which has been de-oxygenated in the system, back to the heart where it can be pumped to the lungs and replenished with fresh oxygen. The veins are not muscular, as are the arteries, and must rely on valves placed at intervals along each vein to prevent blood backing up or reversing its flow due to gravity.

Physiology

When the oxygen-rich blood has been transferred to the tissues by tiny capillaries, small veins, called venules, pick up the de-oxygenated blood. And, in a system that looks much like that of streams and rivers, the smaller venous structures dump the blood into larger and larger veins until the blood finally reaches either the superior vena cava or the inferior vena cava, both of which dump the oxygen-poor blood back into the heart.

Because the veins have thin walls and no significant musculature, the blood must flow along with the help of the skeletal muscles in the body and the pressure from arteries that continue to fill the venous system with blood. The “blood pressure” inside the veins is much less than that of the blood inside the arterial system. Because the blood pressure inside a vein is low, tiny valves are located along each segment of vein to keep the blood flowing in one direction.

Anatomy

There are several large veins that have specific functions. The portal vein carries the nutrients we get from our food and takes the blood from our intestinal system to the liver for further processing. If the liver is damaged, the blood in the portal vein can back up and eventually the pressure in the vein rises. This condition is called portal hypertension.

The only vein in our body that has the purpose of carrying oxygenated blood (as opposed to de-oxygenated blood) is the pulmonary vein. When the lung tissues replenish the blood with oxygen, that blood eventually goes to the ventricles of the heart where it can be pumped back into the system again.

The femoral veins pass through the groin area and carry blood from the legs. We have one femoral vein in each of our upper thighs. The femoral vein can be used in certain medical studies and in cases of cardiac arrest where a big vein is needed to obtain blood samples from the patient.

Diseases

The most common diseases of the veins involve the formation of blood clots inside a vein. This causes the vein to become inflamed and results in the body having to use an alternate route to carry the blood. An inflamed vein is also called phlebitis or thrombophlebitis. A blood clot involving primarily the deep veins of the legs is called a deep vein thrombosis. This kind of blood clot can be very dangerous if the blood clot breaks loose and travels to one of the lungs in a condition called pulmonary embolism.