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Lecture

Mean arterial pressure and its regulation

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Department
Physiology
Course
PSL201Y1
Professor
Christopher Perumalla
Semester
Summer

Description
Mean arterial pressure and its regulation The mean arterial pressure is the average aortic pressure occurring during a cardiac cycle. It is determined by heart rate, stroke volume and total peripheral resistance. Mean Arterial Pressure = Cardiac output  Total peripheral resistance. Cardiac output = Heart rate  stroke volume Therefore, MAP = Heart rate  stroke volume  Total peripheral resistance The mean arterial pressure is the pressure that is needed to drive the blood through the system. If you have a low mean arterial pressure, you are unable to deliver the blood to the brain and the other organs that will be deprived of oxygen and nutriments. In the systemic circuit normally, the MAP is 90 mm of mercury. The central venous pressure is 0 mm of mercury. The pressure gradient driving the blood flow through the systemic circuit is the difference between the mean arterial pressure and the central venous pressure. It is 90 mm of mercury. Total peripheral resistance is whatever pressure that is resisting the blood from flowing. In the systemic circuit, it is the combined resistance of all the organs to and away from them that is called total peripheral resistance. Effects of cardiac output on mean arterial pressure If there is constant cardiac output and constant total peripheral resistance, the mean arterial pressure will be constant. However, an increase in cardiac output leads to an increase in the volume of blood contained in the aorta and an increase in mean arterial pressure when total peripheral resistance remains the same. The blood flows into the aorta faster than it flows out when the cardiac output is increased, increasing the volume of blood in the aorta. The vessel expands by stretching the walls of the aorta causing it to exert a large inward force on the blood so that the pressure on the blood increases. Thus, an increase in the heart rate or stroke volume will lead to an increase in cardiac output which will eventually lead to an increase of mean arterial pressure.Aorta To From heart Flow (CO) Constant MAP Flow systemic organs (a) Increased MAP Flow (CO) Flow An increase in eads to an increase in the when total peripheral cardiac output volume of blood contained in resistance remains the the aorta and an increase in same. mean arterial pressure (b) Aorta To From heart Flow (CO) Constant MAP Flow systemic organs (a) Increased MAP Flow (CO) Flow An increase in eads to an increase in the when total peripheral cardiac output volume of blood contained in resistance remains the the aorta and an increase in same. mean arterial pressure (b)Effects of total peripheral resistance on mean arterial pressure A constant cardiac output leads to an increase in the volume of blood contained in the aorta and an increase in mean arterial pressure. When there is an increase in TPR reduces the blood flow out of the aorta at a constant rate. Therefore, volume of blood in the aorta will increase, the walls of the aorta will stretch and the mean arterial pressure also increases.Increased MAP Flow Flow (CO) leads to an increase in the when total peripheral A constant cardiac output volume of blood contained in resistance increases the aorta and an increase in mean arterial pressure (c) Increased MAP Flow Flow (CO) leads to an increase in the when total peripheral A constant cardiac output volume of blood contained in resistance increases the aorta and an increase in mean arterial pressure (c)Neural control of Mean Arterial Pressure Neural control of mean arterial pressure is done through negative feedback. An example of negative feedback is body temperature control. A change in body temperature is detected by sensors. The sensors monitoring the mean arterial pressure are called the arterial barrel receptors. A fall in the blood volume activates both cardiovascular and renal reflex mechanisms. A loss of blood will lead to an increase in sympathetic activity which in turn increases the heart rate, stroke volume and cardiac output. This increase in sympathetic activity will lead to an increase of vasoconstriction and total peripheral resistance. This all results in the return of the MAP to its normal value. This is possible due to the presence of baroreceptors which are pressure receptors. Baroreceptors are found in the blood vessels and the heart that respond to changes in pressure within the cardiovascular system. Arterial baroreceptors are found in the aortic arch and in the carotid sinuses (brain). When the mean arterial pressure changes, activity in the neurons change. When the pressure is increased in the baroreceptors, there is an increase in action potential frequency. The brain detects changes in action potential and through the sympathetic and parasympathetic systems, causes the heart and blood vessels to alter their function in response.Increased Decreased Normal pressure pressure 110 Arterial pressure (mm Hg) 70 N Action potentials Baroreceptor response (membrane potential, mv) Increased Decreased Baseline frequency action potential action potential frequency frequency Increased Decreased Normal pressure pressure 110 Arterial pressure (mm Hg) 70 N Action potentials Baroreceptor response (membrane potential, mv) Increased Decreased Baseline frequency action potential action potential frequency frequencyBaroreceptors are found in two areas.Arterial baroreceptors Carotid bifurcation Carotid sinus Common carotid artery Aortic arch Arterial baroreceptors Carotid bifurcation Carotid sinus Common carotid artery Aortic archOther cardiovascular regulatory processes Cardiovascular control center The cardiovascular function is regulated primarily by the medulla oblongata that relays signals to the heart and the blood vessels by way of sympathetic and parasympathetic neurons. The medulla oblongata and other regions of the brain receives input from the arterialDorsal motor nuclei of the vagus Cardiovascular control centers Medulla oblongata Parasympathetic preganglionic (vagus nerve) SA node Ventricular myocardium Sympatheti Heart Sympathetic Arterioles Sympathetic Veins Spinal oord Sympathetic chain Fi Dorsal motor nuclei of the vagus Cardiovascular control centers Medulla oblongata Parasympathetic preganglionic (vagus nerve) SA node Ventricular myocardium Sympatheti Heart Sympathetic Arterioles Sympathetic Veins Spinal oord Sympathetic chain Fibaroreceptors and some other sensory receptors throughout the body. The parasympathetic system goes from the CNS to the heart, particularly to the SA node. The sympathetic pathway is much more diverse. The medulla oblongata and other regions of the brain also receive input from other sensory receptors such as
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