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The capillaries are responsible for allowing the blood to receive oxygen through tiny air sacs in the lungs. This is also the site where carbon dioxide exits the blood. This all occurs in the lungs where blood is oxygenated. [28] The blood pressure in blood vessels is traditionally expressed in millimetres of mercury (1 mmHg = 133 Pa).
The term capillary exchange refers to all exchanges at microcirculatory level, most of which occurs in the capillaries. Sites where material exchange occurs between the blood and tissues are the capillaries, which branch out to increase the swap area, minimize the diffusion distance as well as maximize the surface area and the exchange time. [4]
The rate of mean blood flow depends on both blood pressure and the resistance to flow presented by the blood vessels. Mean blood pressure decreases as the circulating blood moves away from the heart through arteries and capillaries due to viscous losses of energy.
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]
In humans, the only significant example is the hepatic portal vein which combines from capillaries around the gastrointestinal tract where the blood absorbs the various products of digestion; rather than leading directly back to the heart, the hepatic portal vein branches into a second capillary system in the liver.
The arterial blood plasma, interstitial fluid and lymph interact at the level of the blood capillaries. The capillaries are permeable and water can move freely in and out. At the arteriolar end of the capillary the blood pressure is greater than the hydrostatic pressure in the tissues.
Blood exits the glomerular capillaries by an efferent arteriole instead of a venule, as is seen in the majority of capillary systems (Fig. 4). [ 3 ] This provides tighter control over the blood flow through the glomerulus, since arterioles dilate and constrict more readily than venules, owing to their thick circular smooth muscle layer ( tunica ...
[1] [2] The peripheral arteries supply oxygenated blood to the body, and the peripheral veins lead deoxygenated blood from the capillaries in the extremities back to the heart. [3] Peripheral veins are the most common intravenous access method in both hospitals and paramedic services for a peripheral intravenous (IV) line for intravenous ...