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Chapter 15 First Half - Blood Flow_Control of BP

Chapter 15 First Half - Blood Flow_Control of BP - Blood...

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Blood vessels contain vascular smooth muscle - Vasoconstriction narrows the diameter, whereas vasodilation widens it. - State of partial contraction at all times (muscle tone) Substantial amounts of energy are required to stretch the walls of an artery outward. This energy comes in the form of high-pressure blood ejected from the left ventricle. Blood flowing through the metarterioles can either go into the capillaries or bypass them and go directly into venous circulation if precapillary sphincters are contracted. - Capillaries only let small substances through (barely large enough to led RBC’s in, let alone WBC’s) Capillaries lack smooth muscle – their walls consist of a flat layer of endothelium. - Pericytes contribute to the “tightness” of capillary permeability: the more pericytes, the less leaky the capillary endothelium. - loss of pericytes around capillaries of the retina is a hallmark of the disease diabetic retinopathy . Veins: more numerous than the arteries; larger diameter as well. - Hold half the blood in the CV system. Angiogenesis – creates new blood vessels in the body. - Vascular endothelial growth factor and fibroblast growth factor promote angiogenesis - Angiostatin and endostatin inhibit angiogenesis. Pressure is created by ventricular contraction this is the driving force for blood flow throughout the CV system: Blood is ejected from the left ventricle, and the aorta and arteries expand to accommodate it. When the ventricle relaxes and aortic semilunar valve closes, the elastic arterial walls recoil, propelling the blood forward into smaller arteries/arterioles. This sustains the driving pressure for blood flow during ventricular relaxation . Blood pressure is the highest in the arteries and lowest in the veins. Aortic pressure occurs in the aorta and reaches an average high of 120 mm Hg during ventricular systole, then falls steadily to a low of 80 mm Hg during ventricular diastole - What we’re measuring when we take the BP is the aortic pressure. Diastolic pressure in the large arteries remains relatively high reflects the ability of these vessels to capture and store energy in their elastic walls.
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