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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. The greatest change in blood pressure and velocity of blood flow ...
Metarterioles connect arterioles and capillaries. A tributary to the venules is known as a thoroughfare channel. [citation needed] The microcirculation has three major components: pre-capillary, capillary, and post-capillary. In the pre-capillary sector, arterioles, and precapillary sphincters participate. Their function is to regulate blood ...
Arterioles; Capillaries (smallest type of blood vessels) Venules; Veins. Large collecting vessels, such as the subclavian vein, the jugular vein, the renal vein and the iliac vein. Venae cavae (the two largest veins, carry blood into the heart). Sinusoids. Extremely small vessels located within bone marrow, the spleen and the liver.
Immediately following the arterioles are the capillaries. Following the logic observed in the arterioles, we expect the blood pressure to be lower in the capillaries compared to the arterioles. Since pressure is a function of force per unit area, (P = F/A), the larger the surface area, the lesser the pressure when an external force acts on it ...
Resistance arteries are usually small arteries or arterioles and include precapillary sphincters. [1] Having thick muscular walls and narrow lumen they contribute the most to the resistance to blood flow. Degree of the contraction of vascular smooth muscle in the wall of a resistance artery is directly connected to the size of the lumen.
There are two types of capillaries: true capillaries, which branch from arterioles and provide exchange between tissue and the capillary blood, and sinusoids, a type of open-pore capillary found in the liver, bone marrow, anterior pituitary gland, and brain circumventricular organs. Capillaries and sinusoids are short vessels that directly ...
The vasa recta of the kidney, (vasa recta renis) are the straight arterioles, and the straight venules of the kidney, – a series of blood vessels in the blood supply of the kidney that enter the medulla as the straight arterioles, and leave the medulla to ascend to the cortex as the straight venules.
Precapillary sphincters and metarterioles were discovered in the mesenteric circulation in the 1950s. Medical and physiological textbooks, such as Guyton, Boron and Fulton, etc. were quick to claim the existence of said sphincters and metarterioles all over the body, despite lack of evidence. [2]