49 - Baroreceptors located in the arterial carotid sinus...

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Unformatted text preview: Baroreceptors - located in the arterial carotid sinus and the aortic arch detect rises and falls in arterial blood pressure. These receptors send signals to the cardiovascular control center in brainstem which then adjusts levels of sympathetic activity. Example: If plasma volume decreases because of hemorrhage, baroreceptors will detect the drop in blood pressure and communicate this drop to the cardiovascular control center. The cardiovascular control center will then coordinate an increase in sympathetic activity. Sympathetic activity will not only increase cardiac output and total peripheral resistance but will also decreases GFR (to maintain plasma volume by constricting afferent arterioles). (note: this response will override the myogenic response) Autoregulation - helps maintain a constant blood flow into the glomerular capillaries. This is accomplished by changing the caliber of the afferent arterioles (note: sympathetic input can override autoregulation). The mechanism(s) for autoregulation are unknown, but they may include: (1) a myogenic mechanism, and/or (2) a tubuloglomerular feedback mechanism. Myogenic mechanism - a common property of vascular smooth muscle is to contract automatically in response to increased stretch and to relax in response to decreased stretch. Tubuloglomerular feedback mechanism (Figures 14-11, 14-12) a feedback process that involves the juxtaglomerular apparatus (the region near the glomerulus where the tubule passes through the fork formed by the afferent and efferent arterioles). Two specialized cell types are located in the juxtaglomerular apparatus: (1) granular cells, and (2) macula densa cells. Granular cells - line arteriolar wall where contact is made with the tubule; contain secretory granules. Macula densa cells - line tubular wall where contact is made with the arterioles. These cells detect changes in the rate fluid is flowing and release local acting vasoactive chemicals (including endothelin- a vasoconstrictor, and bradykinin a vasodilator) to change the diameter of afferent arterioles. ...
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This note was uploaded on 10/29/2009 for the course NPB NPB 101 taught by Professor Weidner/wingfield during the Fall '08 term at UC Davis.

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