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Vein

For the geological use, see vein (geology).

In biology, a vein is a blood vesselwhich carries bloodtoward the heart. Veins form part of the circulatory system. The vessels that carry blood away from the heart are known as arteries.

Biological Vein

Veins have one-way valves to prevent backflow caused by gravity. Image:Veincrosssection.png

In systemic circulationde-oxygenatedblood from the capillaryblood vessels is taken by veins to the right part of the heart. Differently, in the pulmonary circulationoxygenated blood from the lungsis taken to the left part of the heart by pulmonary veins. Another special case is portal circulationwhere the portal veintransports blood rich in products of digestion from the intestinesto the liver.

Names of important veins:

Pulmonary veins
Portal vein
Superior vena cava
Inferior vena cava
Femoral vein
Great saphenous vein

Veins are used medically as points of access to the blood stream, permitting the withdrawal of blood specimens (venipuncture) for testing purposes, and enabling the infusion of fluid, electrolytes, nutrition, and medications. The latter is called intravenous delivery. It can be done by an injection with a syringe, or by inserting a catheter(a flexible tube).

If an intravenous catheter has to be inserted, for most purposes this is done into a peripheral vein (a vein near the surface of the skin in the handor arm, or less desirably, the leg.) Some highly concentrated fluids or irritating medications must flow into the large central veins, which are sometimes used when peripheral access cannot be obtained. Catheters can be threaded into the superior vena cava for these uses: if long term use is thought to be needed, a more permanent access point can be inserted surgically.

The precise location of veins is much more variable from person to person than that of arteries.

Vein

Biological Vein

See also