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48 Cards in this Set

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  • Back
How much can muscle bloodflow increase during exercise?
Up to 20X
How much of an effect does muscle have on CO?
A big one - because it makes up a large portion of body mass.
What is the resting bloodflow of muscle?
3-4 ml/min/100g muscle
What happens to bloodflow through muscles when they become active? How?
Bloodflow increases greatly - because capillary density increases markedly.
When does flow in muscle occur?
Between contractions
What is the nature of bloodflow through a muscle like?
Very rythmic - on during relaxation, off during contraction.
Why is it harder to maintain isometric contractions?
Because there is no relaxation so no time for filling / reperfusion of the muscle.
2 types of control of muscle bloodflow:
1. Local
2. Nervous
Local controllers of muscle bloodflow:
1. Ischemia
2. Vasodilators
How does ischemia regulate muscle bloodflow?
Decreased O2 has a direct effect on smooth muscle to cause vasodilation.
Important vasodilators released from muscle to regulate local bloodflow:
2 Types of Nervous control of muscle bloodflow during exercise:
1. CNS release of NE
2. Adrenal gland release of Epi and Norepi
Where is the sympathetic release of NE more prominent? What type of receptors does it act upon and what is the effect?
More prominent in the kidney and gut; acts on alpha 1 receptors to cause vasoconstriction.
Where is the adrenergic release of Epi and Norepi more prominent? What receptors do they act on and what is the effect?
-More prominent in Active muscle and the liver
-Cause vasodilation when they bind B2-receptors.
What areas are NOT effected much by sympathetic vasoconstriction in response to muscle activity? Why not?
-Brain (no alpha receptors)
-Coronary (needs lots of blood to keep the heart pumping)
When we say there is vasoconstriction and increase in sympathetic tone in response to SNS stimulation, what tissues are we speaking of?
How do you know what the effect of stimulating SNS regulation of circulation will be on skeletal muscle?
Depends on the muscle; if it's exercising it will vasodilate; if it's non-exercising it will constrict.
What are the 7 main circulatory adjustments made during exercise?
1. Mass sympathetic discharge
2. Decreased PNS impulses
3. Increased HR / contractility
4. Increased MAP
5. Local vasodilation in working muscles
6. Global venoconstriction to increase Psf
7. Increased VR/CO
What should you think of when you think of increased sympathetic tone?
-Veins and Psf!!
Why do veins do the most constriction in response to SNS stimulation?
Because their smooth muscle has the most alpha receptors.
Is the bloodflow through a muscle ALWAYS rythmic in nature?
No; only during exercise when it is contracting.
What happens to bloodflow through a muscle at the end of contractions?
Bloodflow remains very high for a few seconds, then fades toward normal in the next few minutes.
Review; what are the 2 types of nervous regulation of skeletal muscle bloodflow?
-Sympathetic vasoconstrictors (and some symp vasodilators)
-Adrenal release of NE/Epi
Sympathetic vasoconstrictors secrete mainly what?
What is the effect of maximally activating sympathetic vasoconstrictors?
Significantly Decreased bloodflow through resting muscles (nonexercising).
What is a more indirect cause of vasoconstriction when SNS outflow is increased?
Release of NE from the adrenal medulla - vs the symp nerves themselves.
What is the effect of Epinephrine released from adrenal medulla glands?
Why does epinephrine cause vasodilation?
Because it acts more on Beta receptors of vessels, and these are vasodilator receptors.
Norepi prefers __ receptors and causes vaso_______
Epi prefers __ receptors and causes vaso_______
Norepi - alpha - vasoconstrict
Epi - beta - vasodilate
Why do such substantial changes need to be made to circulation during exercise?
To supply the tremendous bloodflow required by the muscles.
What are the 3 major effects on circulation that occur during exercise?
1. Mass sympathetic discharge
2. Increased MAP
3. Increased CO
What initiates the mass sympathetic discharge during exercise?
Signals sent to the Vasomotor center simultaneously with voluntary motor efferent signals.
What happens to PNS activity during exercise?
It is attenuated at the same time as SNS discharge is stimulated.
3 major circulatory effects of mass sympathetic discharge:
1. Increased HR/contractility
2. Increases RVR / Psf
3. Increased VR / CO
What vasoconstricts, and what vasodilates during exercise?
What is spared?
Vasoconstrict: splanchnic, renal, and nonexercising muscle
Vasodilate: exercising muscle
-Spared: brain and heart
-Skin has its own regulation
What happens to the MAP of a person that performs very tense tedious work but only uses a few muscles?
MAP goes very high
What happens to a persom that performs massive whole-body exercise like running/swimming?
MAP only increases somewhat because there is extreme vasodilation in the large mass of active muscle.
2 Reasons why increased MAP is important during exercise:
1. It increases force to push blood through muscle tissue vessels
2. Stretches walls of vessels to increase total muscle flow
What factor is just as important for exercise as the strength of muscle doing the work?
The ability of the athlete's body to increase cardiac output.
How does the CO/VR curve change during heavy exercise?
BOTH curves change - There is increased CO and increased VR
Why is CO increased during heavy exercise?
Because of the mass SNS discharge that has 2 effects:
1. Increased HR
2. Increased contractility
What levels of CO can be achieved by hypereffectiveness in untrained runners? in Marathon runners?
Untrained: 4X increase
Marathon: 7X increase
How would CO be affected if VR didn't change at all during heavy exercise?
CO would be limited to the plateau of VR which is normally 6L/min
What 2 changes allow VR to change during heavy exercise?
-Psf increases due to global vasoconstriction and abdominal tensing - increases from 7-30!
-The VR slope increases due to decreased RVR in active muscle
Why is it especially good that the gut and kidney have increased resistance (vasoconstriction) during exercise?
To maintain MAP - otherwise the massive dilation to exercising muscles would decrease MAP and you might faint or die.
What is the effect of exercise on TPR?
It is decreased
Compare TPR at rest vs exercising:
Resting: 100/5 = 20 TPR

Exercising: 120/20 = 6

How is TPR reduced during exercise?
MAP is slightly increased and CO is markedly increased.