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[1] [2] At the point where each of the capillaries originates from an arteriole, contractile mural cells encircle the capillary. This is called the precapillary sphincter. The precapillary sphincter has now also been found in the brain, where it regulates blood flow to the capillary bed. [3]
The heart is the driver of the circulatory system, pumping blood through rhythmic contraction and relaxation. The rate of blood flow out of the heart (often expressed in L/min) is known as the cardiac output (CO). Blood being pumped out of the heart first enters the aorta, the largest artery of the body.
The peripheral vascular system is the part of the circulatory system that consists of the veins and arteries not in the chest or abdomen (i.e. in the arms, hands, legs and feet). [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 ...
Their function is to regulate blood flow before it enters the capillaries and venules by the contraction and relaxation of the smooth muscle found on their walls. 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.
In the lungs, special mechanisms have been adapted to meet the needs of increased necessity of blood flow during exercise. When the heart rate increases and more blood must flow through the lungs, capillaries are recruited and are also distended to make room for increased blood flow. This allows blood flow to increase while resistance decreases.
Precapillary resistance is the modulation of blood flow by capillaries through vasomotion, either opening and letting blood pass through, or by constricting their lumens, reducing bloodflow through the capillary bed (occluding the passage of blood).
Pericytes also project finger-like extensions that wrap around the capillary wall, allowing the cells to regulate capillary blood flow. [6] Both pericytes and endothelial cells share a basement membrane where a variety of intercellular connections are made.
Endothelins help to regulate capillary exchange and alter blood flow by their constriction of the smooth muscle in the walls. Vasoconstriction increases blood pressure , and its overexpression can contribute to hypertension and cardiovascular disease .