Vein

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Vein med.jpg

Veins are one of the five different types of blood vessels that make up the circulatory system. (Arteries, Arterioles, Venules and Capillaries being the others)

The majority of veins carry deoxygenated blood to the heart apart from the pulmonary vein that carries oxygenated blood to the heart. The walls of veins are made of three layers:

  1. The tunica intima consisting of a layer of flat endothelial cells overlaying a thin layer of connective tissue.
  2. The tunica media  consisting of circular layer of smooth muscle containing elastin and collagen. This provides mechanical strength for the vein.
  3. The tunica adventitia consisting of a layer of elastic and collagenous fibres fixed along the length of the vessel[1].

The blood pressure in veins in very low, compared to the blood pressure in arteries and therefore veins have valves which stop the backflow of blood. Skeletal muscles also help deoxygenated blood in the vein to get back into the heart by squeezing the vein when they contract. Finally, veins branch into venules which join the capillaries in the body.

References:

  1. Pocock G.,Richards C.(2006) Human Physiology: The Basis of Medicine, 3rd Edition, Oxford University Press. Chapter 15 - Pg 264
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