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BIOC33H3 (127)
Lecture

Lecture_8_Notes.rtf

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Department
Biological Sciences
Course
BIOC33H3
Professor
Stephen Reid
Semester
Summer

Description
1Lecture 8 Blood Pressure Regulation and an Introduction to the Respiratory System1 The Baroreflex and BaroreceptorsTo date almost all of the cardiovascular system concepts and control systems that we have discussed will affect blood pressure If blood pressure is changing then nervous hormonal and local effects will all converge to affect either cardiac output by altering stroke volume or heart rate or total peripheral resistance Much of blood pressure regulation is extrinsic to blood vessels occurring as a result of nervous or hormonal input conversely some of the regulation as detailed in the previous lecturelocal control of blood flow is intrinsic to vessels blood vessels or the organs which they supply There are also differences in the regulation of blood pressure over the short term that is over seconds or minutes and its regulation over the longterm from minutes to days The latter have more to do with fluid balance and excretion of fluid from the kidneys or retention of fluid at the kidneysOver the short term acute regulation of blood pressure is accomplished with a reflex circuit termed the baroreflex The baroreflex is a set of reflex responses with occur in response to stimulation or inhibition or a reduction of stimulation of baroreceptors blood pressure sensor cells which are located in blood vessels throughout the circulatory system A very common and important example of the baroreflex response occurs in response to a decrease in mean arterial pressure A decrease in MAP is sensed by the baroreceptors and they in turn cause an increase in sympathetic output and a decrease in parasympathetic output This leads to increases in HR SV and TPR and therefore an increase in MAP If blood pressure were to increase then the baroreceptors would cause the opposite to occur a decrease in sympathetic activity and an increase in parasympathetic activity Keep in mind that baroreceptor activity increases in response to high blood pressure and decreases in response to low blood pressure see below2 Aortic Arch and Carotid Sinus Baroreceptors The two main populations of baroreceptors in our circulation are located within the arterial side of the circulation positioned to monitor blood flow to the systemic circuit and to the brain The first of these baroreceptor populations is located in the aortic arch just as the aorta leaves the left ventricle and begins to curve downward These baroreceptors are well positioned to sense the pressure of blood flowing to the entire body systemic circuitFurther upward along the common carotid artery is a little bulge or sinus in the blood vessel called the carotid sinus The baroreceptors in the carotid sinus are well positioned to sense the pressure of blood flowing to the brain The common carotid artery bifurcates into external and internal vessels downstream from the carotid sinus and just before that bifurcation lies a small organ called the carotid body which is the primary location of arterial oxygen chemoreceptors On a perweight basis the carotid body receives more blood flow than any other organ in the body including the brain Both types of baroreceptors carotid sinus and aortic arch send signals to the brain stem
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