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Post-capillary venules are the smallest of the veins with a diameter of between 10 and 30 micrometres (μm). When the post-capillary venules increase in diameter to 50μm they can incorporate smooth muscle and are known as muscular venules. [1] Veins contain approximately 70% of total blood volume, while about 25% is contained in the venules. [2]
The second sector is the capillary sector, which is represented by the capillaries, where substance and gas exchange between blood and interstitial fluid takes place. Finally, the post-capillary sector is represented by the post-capillary venules, which are formed by a layer of endothelial cells that allow free movement of some substances. [3]
A capillary is a small blood vessel, from 5 to 10 micrometres in diameter, and is part of the microcirculation system. Capillaries are microvessels and the smallest blood vessels in the body. They are composed of only the tunica intima (the innermost layer of an artery or vein), consisting of a thin wall of simple squamous endothelial cells. [2]
The venous system apart from the post-capillary venules is a high volume, low pressure system. Vascular smooth muscle cells control the size of the vein lumens, and thereby help to regulate blood pressure. [31] The post-capillary venules are exchange vessels whose ultra-thin walls allow the ready diffusion of molecules from the capillaries. [10]
Blood vessels function to transport blood to an animal's body tissues. In general, arteries and arterioles transport oxygenated blood from the lungs to the body and its organs, and veins and venules transport deoxygenated blood from the body to the lungs. Blood vessels also circulate blood throughout the circulatory system.
The capillaries connect to venules, and the blood then travels back through the network of veins to the venae cavae into the right heart. The micro-circulation — the arterioles, capillaries, and venules —constitutes most of the area of the vascular system and is the site of the transfer of O 2, glucose, and enzyme substrates into the
Capillary walls contain of a monolayer of endothelial cells. There are two ways for molecules to diffuse through the endothelial monolayer: through gaps between the cells or directly through the cells. Molecules diffuse through the capillary walls due to concentration gradients. Diffusion between the cells changes depending upon the type of ...
Lymph capillaries or lymphatic capillaries are tiny, thin-walled microvessels located in the spaces between cells (except in the central nervous system and non-vascular tissues) which serve to drain and process extracellular fluid. Upon entering the lumen of a lymphatic capillary, the collected fluid is known as lymph.