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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.
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.
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 ...
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]
The arterioles supply capillaries, which in turn empty into venules. The first branches off of the aorta are the coronary arteries , which supply blood to the heart muscle itself. These are followed by the branches of the aortic arch, namely the brachiocephalic artery , the left common carotid , and the left subclavian arteries.
In the human descending aorta, vasa vasorum cease to supply the arterial tunica media with oxygenated blood at the level of the renal arteries. [5] Thus, below this point, the aorta is dependent on diffusion for its metabolic needs, and is necessarily markedly thinner.