Download AHS CVS Lecture 6

THE CARDIOVASCULAR SYSTEM
LECTURE 6:
REGULATION OF BLOOD PRESSURE
Dr. Eamonn O’Connor
Allied Health Sciences
Lecture Outline
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Determinants of Mean Arterial Pressure
  Regulation of Mean Arterial Pressure
  Control of Blood Pressure by Arterial Baroreceptors
  Baroreceptor reflex
  Hormonal control of Mean Arterial Pressure
 
AHS Physiology - Cardiovascular System 11-12
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Determinants of Mean Arterial Pressure
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 
Mean arterial pressure determined by:
  Heart
rate
  Stroke volume
  Total peripheral resistance
 
MAP = CO x TPR
  CO
= HR x SV
  MAP = HR x SV x TPR
AHS Physiology - Cardiovascular System 11-12
Regulation of MAP
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 
Flow = pressure gradient / resistance
  CO
= MAP / TPR
  Therefore MAP = CO x TPR
  MAP
 
= HR x SV x TPR
TPR = Total peripheral resistance
  Combined
  Consider
 
resistance of all blood vessels
the importance of vasodilation & vasoconstriction
This means that MAP is completely determined by
HR, SV, and TPR
AHS Physiology - Cardiovascular System 11-12
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Effects of Cardiac Output on MAP
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AHS Physiology - Cardiovascular System 11-12
Figure 14.25a, b
Effect of Total Peripheral Resistance on MAP
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AHS Physiology - Cardiovascular System 11-12
Figure 14.25a, c
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Blood Pressure: Mean Arterial Pressure
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MAP = driving force for blood flow
  F = ΔP/R
 
  Regulating
MAP critical to normal function
  MAP < normal
  Hypotension
  Inadequate
  MAP
blood flow to tissues
> normal
  Hypertension
  Stress
on heart and walls of blood vessels
AHS Physiology - Cardiovascular System 11-12
Short and Long-Term Regulation of MAP
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 
Short-term regulation – seconds to minutes
  Involves
heart and blood vessels
  Primarily neural control
 
Long-term regulation – minutes to days
  Regulate
blood volume
  Involves kidneys
  Primarily hormonal control
AHS Physiology - Cardiovascular System 11-12
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Neural Control of MAP
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 
Negative feedback loops
  Detector
= baroreceptors
  Integration Center = cardiovascular centers in the
brainstem
  Controllers = autonomic nervous system
  Effectors = heart and blood vessels
AHS Physiology - Cardiovascular System 11-12
Arterial Baroreceptors
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 
Baroreceptors =
stretch receptors
  Arterial
baroreceptors
  High
pressure
baroreceptors
  Sinoaortic
baroreceptors
 
Location
  Carotid
sinus
  Aortic arch
AHS Physiology - Cardiovascular System 11-12
Figure 14.26
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Response of Baroreceptors
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AHS Physiology - Cardiovascular System 11-12
Figure 14.27
Cardiovascular Control Center
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 
Medulla oblongata
  Integration
center for blood pressure regulation
AHS Physiology - Cardiovascular System 11-12
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Cardiac and Venous Baroreceptors
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 
Location
  Walls
of large systemic veins
  Walls of the atria
 
Low pressure baroreceptors = volume receptors
  Decrease
in blood volume activates receptors
triggering responses that act in parallel with
baroreceptor reflex
AHS Physiology - Cardiovascular System 11-12
Cardiovascular Control Center
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 
Output
  Sympathetic
nervous system
  Parasympathetic nervous system
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Autonomic Output to Cardiovascular Effectors
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 
Parasympathetic input to:
  SA
node (decrease HR)
  AV node
 
Sympathetic input to:
  SA
node (increase HR)
  AV node
  Ventricular myocardium (increase contractility)
  Arterioles (increase resistance)
  Veins (increase venomotor tone)
AHS Physiology - Cardiovascular System 11-12
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Major Neural Pathways in the Control
of Cardiovascular Function
AHS Physiology - Cardiovascular System 11-12
Figure 14.28
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Components of Baroreceptor Reflex
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Baroreceptor reflex = Negative feedback loop
  Function:
 
  Maintain
 
BP (MAP) at normal levels
Detectors = baroreceptors
  Afferents
= nerves
  Integration center = cardiovascular control center
  Efferents = autonomic nervous system
  Effectors = heart, arterioles, veins
AHS Physiology - Cardiovascular System 11-12
Example of the Baroreceptor Reflex
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 
A person who had been lying down stands up
quickly:
  Gravity
causes venous pooling in the legs.
  This causes a decrease in VR, causing a decrease in CO
  This causes a decrease in blood pressure.
  Baroreceptors sense the decrease: reflex occurs
  The reflex causes increased sympathetic and decreased
parasympathetic activity.
  CO and TPR are increased.
  Blood pressure is increased back to normal.
AHS Physiology - Cardiovascular System 11-12
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Baroreceptor Reflex in Response
to a Decrease in MAP
MAP
Arterial baroreceptors
Frequency of
action potentials
conducted to CNS
Cardiovascular control center
Parasympathetic activity
SA node
Sympathetic activity
Ventricular myocardium
Action potential
frequency
Contractility
Veins
Venomotor tone
Arterioles
Vasoconstriction
Compliance
Venous pressure
Negative
feedback
EDV
HR
SV
TPR
MAP
AHS Physiology - Cardiovascular System 11-12
Figure 14.29
Hormonal Control of MAP
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 
Epinephrine:
  Released
by adrenal medulla in response to
sympathetic activity
  Increases mean arterial pressure
  Acts on heart
  Increases
  Increases
  Acts
on smooth muscle of arterioles
  Increases
  Acts
HR
SV
TPR
on smooth muscle of veins
  Increases
venomotor tone
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Vasopressin and Angiotensin II
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 
Vasoconstrictors
  Increase
TPR
  Increase MAP
AHS Physiology - Cardiovascular System 11-12
Summary of Cardiovascular Physiology
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AHS Physiology - Cardiovascular System 11-12
Figure 13.2
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