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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]
The short distance is important because the capillary diffusion rate decreases when the diffusion distance increases. Then, because of its large number (10-14 million capillaries), there is an incredible amount of surface area for exchange. However, this only has 5% of the total blood volume (250 ml 5000 ml).
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
In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. [1] [2] It includes the cardiovascular system, or vascular system, that consists of the heart and blood vessels (from Greek kardia meaning heart, and Latin vascula meaning vessels).
There are five types of blood vessels: the arteries, which carry the blood away from the heart; the arterioles; the capillaries, where the exchange of water and chemicals between the blood and the tissues occurs; the venules; and the veins, which carry blood from the capillaries back towards the heart.
Human behavior is studied by the social sciences, which include psychology, sociology, ethology, and their various branches and schools of thought. [1] There are many different facets of human behavior, and no one definition or field study encompasses it in its entirety. [2]
An arteriole is a small-diameter blood vessel in the microcirculation that extends and branches out from an artery and leads to capillaries. [1]Arterioles have muscular walls (usually only one to two layers of smooth muscle cells) and are the primary site of vascular resistance.
High endothelial venules (HEV) are specialized post-capillary venules characterized by plump endothelial cells as opposed to the usual flatter endothelial cells found in regular venules. [1] HEVs enable lymphocytes circulating in the blood to directly enter a lymph node (by crossing through the HEV).