Circulation%202 - Circulation 2 Modulation of peripheral...

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Circulation 2: Modulation of peripheral resistance peripheral resistance is actually proportional to 1/r 4 (r is the radius) -- so slight change in vessel diameter produces a huge change in resistance is generally thought that the major vessels whose diameter controls blood pressure are the arterioles , but recent evidence suggests that major arteries, and even veins can change their diameter nervous control vasoconstrictor nerves from the vasomotor center (in the medulla of the brain) innervate many blood vessels and maintain a slight constriction of the vessels. This action can be inhibited by activation of a vasodilator center in the vasomotor center by an increase in blood pressure--sensed by the baroreceptors in the aorta and carotid. Nerve impulses from the VD center inhibit the VC center. hormonal control Vasopressin (peptide) is released from the pituitary gland in the brain when the baroreceptors sense a fall in blood pressure--produces vasoconstriction Angiotensin (peptide) produced in the blood when the kidney senses a fall in blood pressure--produces vasoconstriction Endothelin (peptide) is released from the endothelium (cells lining the blood vessels), after vascular damage, and produces vasoconstriction of the underlying
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