Physiology 3120 Lecture Notes - Lecture 38: Mean Arterial Pressure, Baroreflex, Vascular Resistance

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Human Physiology Lecture 38
Baroreceptor Reflex + CV Control Centre
January 14 2018
- Baroreceptor is all about maintaining MAP at constant levels
o Do not want it too high or too low
o Monitor BP + blood volume through special mechanoreceptors
- Overall purpose of the neural control mechanism is to maintain normal arterial pressure for proper
perfusion of tissues throughout the body + it involves rapid adjustment to both cardiac output and
peripheral resistance
CV Regulator Mechanisms
Mechanisms for the control of circulation:
(i) Local mechanisms (autoregulation)
1. Myogenic theory
2. Metabolic theory
3. Humoral mechanisms
4. Vasoconstrictors (increase MAP)
5. Vasodilators (decrease MAP)
(ii) Neural mechanisms (ANS)
1. Cholinergic decreases MAP
2. Adrenergic increases MAP
- PNS predominately controls the heart + DOES NOT have a direct effect on blood vessels
o Acetylcholine binds muscarinic receptors; SA node, AV node
o PNS decreases HR + force of contraction
o KNOW THE MECHANISM OF HOW ACH CHANGES HR + SV All about changing the
conductance of ions, whether its in the SA nodal cells (pace maker potential decrease
slope + hyperpolarize it, taking longer to reach threshold and decrease HR)
o When you shut off the SNS blood vessels dilate
o Overall, PNS decreases MAP
- SNS
o Nerves directly innervate blood vessels + heart
o Neurotransmitter is NOREPINEPHRINE
Binds BETA1 receptors in the heart and BETA2 receptors in the vessels
o Increase HR+ force of contraction
Changing the slope of the pacemaker potential increasing the slope increases HR
Increase the amount of calcium entering heart contractile cells increase SV
o Blood vessels
Releasing NE on the blood vessels and bind BET1 receptors causing
vasoconstriction
General effect of most blood vessels in the body
o There may be cholinergic vasodilator fibers to cardiac muscle, skeletal muscle + liver
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Release Ach causing vasodilation in these areas
o Innervates the adrenal gland releases ACh onto it
Adrenal gland predominantly releases Epinephrine with some NE circulate
around in the blood, and bind to their particular receptors
- ALPHA CONSTRICT, BETA DILATES
o Alpha 1 = general vasoconstriction throughout the body
o Beta 2 = vasodilates in the smooth muscle, cardiac muscle & liver
ONLY epinephrine binds it, NOT NE
- Sympathetic nervous system can also stimulate contraction of the veins
o Veins increase venous return = increase EDV = SV = increase CO = increase MAP
- Vasodilator metabolites are produced by exercising tissue can block the effects of NE + E on
adrenergic receptors
o Shut off in the active tissues want to increase blood flow to these areas
The Baroreceptor Reflex:
- Homeostatic mechanism (neg feedback)
- Maintains normal mean arterial pressure for proper perfusion of tissues throughout the body
o If BP is too low faint because the blood flow to the brain is too low
o If BP is too high causes cardiovascular disease
o MAINTAINS
- Involves rapid adjustments to both cardiac output and total peripheral resistance
o Neuro impacts RAPID
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- Mechanism that kicks in when you’ve been sitting down for a long time and suddenly stand up
blood pools to your legs and your blood pressure drops
o Baroreceptor reflex helps bring up the blood pressure
- Mean Arterial Pressure = CO X TPR
Heart and Blood Vessels
- Tap = heart, regulating CO
- Blood vessels regulating TPR
- Always want to maintain MAP
Baroreceptor Reflex
- Relies on specialized structures:
o Mechanoreceptors
Higher pressure baroreceptors
Located in the aortic arch and carotid sinus
Are involved with the baroreceptor reflex
Low pressure volume receptors (not involved in baroreceptor reflex)
Act more like volume receptors monitor volume in blood in the
cardiovascular system
Are NOT involved with the baroreceptor reflex
o CV control centre in medulla of the brain stem
Where the information is coming in from the receptors + ensures that the input
from the receptors matches the set point
Monitor input of information + regulating output of information
Cardiovascular control center!
If information from the receptors changes then it causes a change in CO, or TPR to
help maintain the MAP
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