PHYS20008 Lecture Notes - Lecture 18: Vascular Resistance, Autonomic Nervous System, Vasoconstriction
12 Jun 2018
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Lecture 18
PHYS20008 - HUMAN PHYSIOLOGY
LECTURE 18
CARDIOVASCULAR CHALLENGES
OVERVIEW
•Exercise
•Re-distribution of blood flow
•Vasoconstriction and specific vasodilation
•Cardiac Output and TPR
•Effects on MAP
•Temperature control and fluid loss
EXERCISE CHALLENGES
•Increased metabolic demand of muscles. Increased demand means we need to dilate the blood
vessels in order to reach the organs under demand. With increased demand we also want to move
more blood through to feed it
•Delivery of nutrients
•Demand varies enormously
•Redistribute blood flow as appropriate
•Mechanism?
•Removal of waste
•Maintenance of body temperature
•MAP = CR * total peripheral resistance
•Stroke volume (SV) is a factor of venous return (VR) and contractility.
•Q. During exercise, the activity of which neurons of the autonomic nervous system will
predominate, and what direct effect will this have overall on the diameter of blood vessels?
•1) Parasympathetic
•A. 2) Sympathetic: obvious. Getting us ready for activity. In general it tries to constrict vessels in
the body, using alpha 1 receptors. Thus 3, not 4.
•A. 3) Vasoconstriction:
•4) Vasodilation
EXERCISE: JUST BEFORE & INITIALLY
•Anticipation and initial movement causes:
•Activation of the sympathetic nerves
•Suppression of parasympathetic nerves
•Increased HR
•Increased myocardial contractility
•Increased tone in blood vessels (vasoconstriction)
•All before exercise has produced changes
•Eg. before drop in pO2 and rise in pCO2
•Feed forward anticipation in brain for exercise. Parameters increase before the exercise actually
begins.
EXERCISE: INCREASING DEMAND
•Generalised vasoconstriction
•From sympathetic stimulation of peripheral vessels
Lecture 18
PHYS20008 - HUMAN PHYSIOLOGY
•Q. Which organs do you predict should have stable or increased blood flow during moderate
exercise?
•A. 1) Heart
•A. 2) Brain
•A. 3) Skeletal muscle
•4) Kidney
•5) Stomach
•A. 6) Liver
•Don’t wanna decrease blood flow to brain obviously because we get light headed but we don’t
wanna increase and cause a hemorrhage either, so stays stable.
•Kidney doesn’t need specific blood flow for exercise. It usually takes a massive amount of our
cardiac output.
•How maintain/increase flow to certain organs?
•Mechanism behind changed blood flow?
•Has to do with beta 2 receptors. Organ can call for more blood if needed.
•Organ can put out signals to call for more blood, including high levels of CO2, or low
levels of O2, or lactic acid, or, indirectly, a drop in pH.
•Blood flow to active muscles
•Things given off by the muscle stimulate vessel leading into the muscle to dilate. Muscles
that aren’t working won’t give off these signals, so their arterioles will remain constricted.
•Local vasoactive mediators and metabolic changes
•Eg. high CO2, low pH, low O2. Active: vasodilation, inactive: vasoconstriction.
•Balance between sympathetic nervous tone & local effects
•Blood flow to brain remains steady (i.e. local effects dominate)
DISTRIBUTION OF CO2 DURING EXERCISE
•Massive
change to
heart.
•Diagram
(right).
•So on the
left there’s
13% next
to the
brain and
on the
right
there’s
5.2%. This
does not
mean it
decreases.
The 5.2%
is a
smaller
percentage
of a bigger
cardiac
output.
•So look at
the pink
numbers; !
Document Summary
Overview: exercise, re-distribution of blood flow, vasoconstriction and specific vasodilation, cardiac output and tpr, effects on map, temperature control and fluid loss. Increased demand means we need to dilate the blood vessels in order to reach the organs under demand. During exercise, the activity of which neurons of the autonomic nervous system will predominate, and what direct effect will this have overall on the diameter of blood vessels: 1) parasympathetic, a. In general it tries to constrict vessels in the body, using alpha 1 receptors. Exercise: increasing demand: generalised vasoconstriction, from sympathetic stimulation of peripheral vessels. Which organs do you predict should have stable or increased blood flow during moderate. 6) liver: don"t wanna decrease blood flow to brain obviously because we get light headed but we don"t wanna increase and cause a hemorrhage either, so stays stable, kidney doesn"t need specific blood flow for exercise.
