Help building the largest human-edited directory of the web Suggest URL - Open Directory Project - Become an editor

directopedia.org uses links and structure from dmoz Open Directory Project.
The contents has been generating using technology developed by scientec.

For the geological use, see vein (geology).

In biology, a vein is a blood vessel which returns blood from the microvasculature to the heart. Veins form part of the circulatory system. The vessels carrying blood away from the heart are known as arteries.

Biological Vein

Veins have one-way valves to prevent backflow caused by gravity.

In systemic circulation de-oxygenated blood from the capillary blood vessels is taken by veins to the right part of the heart. Differently, in the pulmonary circulation oxygenated blood from the lungs is taken to the left part of the heart by pulmonary veins. Another special case is portal circulation where the portal vein transports blood rich in products of digestion from the intestines to 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 hand or 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.

See also

• Deep vein
• Deep vein thrombosis
• Superficial vein
• Varicose vein

Cardiovascular system	edit
Heart - Aorta - Arteries - Arterioles - Capillaries - Venules - Veins - Venae cavae - Pulmonary arteries - Lungs - Pulmonary veins - Blood

This article is based on the article "Venous" from Wikipedia - the free encyclopedia created and edited by online user community. This article is distributed under the terms of GNU Free Documentation License. Here you find the list of authors of this article. The article can only edited within Wikipedia. Edit this article in Wikipedia.