Physiology 2130 Lecture Notes - Lecture 39: Atrial Natriuretic Peptide, Baroreflex, Carotid Sinus
1 May 2018
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Lecture 039: Baroreceptor reflex and CV control center
Lecture outline
● Baroreceptor
● Response to an increase BP
● Response to a decrease in BP
● CV regulation during stress and exercise
The Baroreceptor Reflex
● Homeostatic mechanism
○ Negative feedback
● Maintains normal mean arterial pressure
○ For proper perfusion of the tissue throughout the body
● Involves rapid adjustments to CO and TPR
○ Recall MAP = CO x TPR
● Relies on specialized structures
○ Mechanoreceptors
■ Higher pressure baroreceptor
● Located in the aortic arch and carotid sinuses
■ Low pressure volume receptors
● Not involved in the baroreceptor reflex
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● Measure the volume of blood in the cardiac system
○ CV control center
■ Located in the medulla (brainstem)
■ Monitors input and regulates output of the
negative feedback system
■ Receives information from the receptors
■ Changes CO and TPR to maintain MAP
High Pressure Baroreceptors
● Located in the walls (tunica externa) of
○ The aortic arch
○ The carotid sinus
● Stretch sensitive receptors
○ Constantly monitor changes arterial pressure
○ Relay information to the CV centre
● Increased BP stretches the walls of blood vessels
○ Stretch Increases the firing rate of APs by the
baroreceptors
○ This increase in AP signals the increase of BP to
the CV centre
○ If the BP drops and stretch will decrease, this will decrease the firing rate of the
baroreceptors
Low Pressure Volume Receptors
● Not involved in the baroreceptor reflex
● Located in the left and the right atrium
○ Predominantly in the right atrium (venous side, where the majority of the blood is
located)
● Detects the “fullness of circulation”
● Helps regulate blood volume
● Blood pressure is directly related to blood volume
○ The higher the blood volume, the higher the MAP (and visa versa)
● Drop in blood volume (which also drops MAP) causes:
○ Release of ADH
■ Humoral mechanism
■ Helps retain water (kidneys to reabsorb water)
■ Causes vasoconstriction in when it is in high concentration
○ Release of renin (which is made into Ang II)
■ Ang II is a strong vasoconstrictor
■ Ang II also stimulate the sensation thirst
● Helps replace blood volume
● Increase in blood volume (which also cause an increase in MAP) causes:
○ Decrease in ADH, renin, Ang II
■ Decrease water reabsorption and vasoconstriction
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○ Increased atrial natriuretic factor release
■ Humoral vasodilator
Baroreceptors Reflex
● Inputs: Have afferent nerves that send signals to the CV centre in the medulla
○ Aortic baroreceptors: via the vagus nerve
○ Carotid sinus baroreceptors: via the carotid sinus nerves
○ Can be both myelinated or unmyelinated fibers
● Output:
○ PNS efferent nerve of the vagus nerve travels from the CV centre to the heart
■ Innervates the SA and AV node (and the cardiac contractile cells)
● Release ACh
○ Decrease HR
○ Decrease force of contraction
○ SNS nerves first travel down and exit the spinal cord to synapse on the
sympathetic ganglion
○ Some SNS postganglionic fibers travel to the heart
■ Innervate the SA node, AV node, and the cardiac contractile cells
● Release Norepinephrine
○ Increase HR
○ Increase force of contraction
○ Other SNS postganglionic fibers travel to the vasculature
■ Innervate the arterioles and the veins
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Document Summary
Lecture 039: baroreceptor reflex and cv control center. For proper perfusion of the tissue throughout the body. Located in the aortic arch and carotid sinuses. Measure the volume of blood in the cardiac system. Monitors input and regulates output of the negative feedback system. Changes co and tpr to maintain map. Located in the walls (tunica externa) of. Increased bp stretches the walls of blood vessels. Stretch increases the firing rate of aps by the baroreceptors. This increase in ap signals the increase of bp to the cv centre. If the bp drops and stretch will decrease, this will decrease the firing rate of the baroreceptors. Located in the left and the right atrium. Predominantly in the right atrium (venous side, where the majority of the blood is located) Blood pressure is directly related to blood volume. Increase in blood volume (which also cause an increase in map) causes:
