3. Muscle Bloodflow And Cardiac Output During Exercise

Front 1

How much can muscle bloodflow increase during exercise?

Back 1

Up to 20X

Front 2

How much of an effect does muscle have on CO?

Back 2

A big one - because it makes up a large portion of body mass.

Front 3

What is the resting bloodflow of muscle?

Back 3

3-4 ml/min/100g muscle

Front 4

What happens to bloodflow through muscles when they become active? How?

Back 4

Bloodflow increases greatly - because capillary density increases markedly.

Front 5

When does flow in muscle occur?

Back 5

Between contractions

Front 6

What is the nature of bloodflow through a muscle like?

Back 6

Very rythmic - on during relaxation, off during contraction.

Front 7

Why is it harder to maintain isometric contractions?

Back 7

Because there is no relaxation so no time for filling / reperfusion of the muscle.

Front 8

2 types of control of muscle bloodflow:

Back 8

1. Local
2. Nervous

Front 9

Local controllers of muscle bloodflow:

Back 9

1. Ischemia
2. Vasodilators

Front 10

How does ischemia regulate muscle bloodflow?

Back 10

Decreased O2 has a direct effect on smooth muscle to cause vasodilation.

Front 11

Important vasodilators released from muscle to regulate local bloodflow:

Back 11

-K
-Adenosine
-Lactate/Co2
-ATP

Front 12

2 Types of Nervous control of muscle bloodflow during exercise:

Back 12

1. CNS release of NE
2. Adrenal gland release of Epi and Norepi

Front 13

Where is the sympathetic release of NE more prominent? What type of receptors does it act upon and what is the effect?

Back 13

More prominent in the kidney and gut; acts on alpha 1 receptors to cause vasoconstriction.

Front 14

Where is the adrenergic release of Epi and Norepi more prominent? What receptors do they act on and what is the effect?

Back 14

-More prominent in Active muscle and the liver
-Cause vasodilation when they bind B2-receptors.

Front 15

What areas are NOT effected much by sympathetic vasoconstriction in response to muscle activity? Why not?

Back 15

-Brain (no alpha receptors)
-Coronary (needs lots of blood to keep the heart pumping)

Front 16

When we say there is vasoconstriction and increase in sympathetic tone in response to SNS stimulation, what tissues are we speaking of?

Back 16

-Splanchnic
-Renal

Front 17

How do you know what the effect of stimulating SNS regulation of circulation will be on skeletal muscle?

Back 17

Depends on the muscle; if it's exercising it will vasodilate; if it's non-exercising it will constrict.

Front 18

What are the 7 main circulatory adjustments made during exercise?

Back 18

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

Front 19

What should you think of when you think of increased sympathetic tone?

Back 19

-Splanchnic/gut
-Veins and Psf!!

Front 20

Why do veins do the most constriction in response to SNS stimulation?

Back 20

Because their smooth muscle has the most alpha receptors.

Front 21

Is the bloodflow through a muscle ALWAYS rythmic in nature?

Back 21

No; only during exercise when it is contracting.

Front 22

What happens to bloodflow through a muscle at the end of contractions?

Back 22

Bloodflow remains very high for a few seconds, then fades toward normal in the next few minutes.

Front 23

Review; what are the 2 types of nervous regulation of skeletal muscle bloodflow?

Back 23

-Sympathetic vasoconstrictors (and some symp vasodilators)
-Adrenal release of NE/Epi

Front 24

Sympathetic vasoconstrictors secrete mainly what?

Back 24

Norepinephrine

Front 25

What is the effect of maximally activating sympathetic vasoconstrictors?

Back 25

Significantly Decreased bloodflow through resting muscles (nonexercising).

Front 26

What is a more indirect cause of vasoconstriction when SNS outflow is increased?

Back 26

Release of NE from the adrenal medulla - vs the symp nerves themselves.

Front 27

What is the effect of Epinephrine released from adrenal medulla glands?

Back 27

Vasodilation

Front 28

Why does epinephrine cause vasodilation?

Back 28

Because it acts more on Beta receptors of vessels, and these are vasodilator receptors.

Front 29

Norepi prefers __ receptors and causes vaso_______
Epi prefers __ receptors and causes vaso_______

Back 29

Norepi - alpha - vasoconstrict
Epi - beta - vasodilate

Front 30

Why do such substantial changes need to be made to circulation during exercise?

Back 30

To supply the tremendous bloodflow required by the muscles.

Front 31

What are the 3 major effects on circulation that occur during exercise?

Back 31

1. Mass sympathetic discharge
2. Increased MAP
3. Increased CO

Front 32

What initiates the mass sympathetic discharge during exercise?

Back 32

Signals sent to the Vasomotor center simultaneously with voluntary motor efferent signals.

Front 33

What happens to PNS activity during exercise?

Back 33

It is attenuated at the same time as SNS discharge is stimulated.

Front 34

3 major circulatory effects of mass sympathetic discharge:

Back 34

1. Increased HR/contractility
2. Increases RVR / Psf
3. Increased VR / CO

Front 35

What vasoconstricts, and what vasodilates during exercise?
What is spared?

Back 35

Vasoconstrict: splanchnic, renal, and nonexercising muscle
Vasodilate: exercising muscle
-Spared: brain and heart
-Skin has its own regulation

Front 36

What happens to the MAP of a person that performs very tense tedious work but only uses a few muscles?

Back 36

MAP goes very high

Front 37

What happens to a persom that performs massive whole-body exercise like running/swimming?

Back 37

MAP only increases somewhat because there is extreme vasodilation in the large mass of active muscle.

Front 38

2 Reasons why increased MAP is important during exercise:

Back 38

1. It increases force to push blood through muscle tissue vessels
2. Stretches walls of vessels to increase total muscle flow

Front 39

What factor is just as important for exercise as the strength of muscle doing the work?

Back 39

The ability of the athlete's body to increase cardiac output.

Front 40

How does the CO/VR curve change during heavy exercise?

Back 40

BOTH curves change - There is increased CO and increased VR

Front 41

Why is CO increased during heavy exercise?

Back 41

Because of the mass SNS discharge that has 2 effects:
1. Increased HR
2. Increased contractility

Front 42

What levels of CO can be achieved by hypereffectiveness in untrained runners? in Marathon runners?

Back 42

Untrained: 4X increase
Marathon: 7X increase

Front 43

How would CO be affected if VR didn't change at all during heavy exercise?

Back 43

CO would be limited to the plateau of VR which is normally 6L/min

Front 44

What 2 changes allow VR to change during heavy exercise?

Back 44

-Psf increases due to global vasoconstriction and abdominal tensing - increases from 7-30!
-The VR slope increases due to decreased RVR in active muscle

Front 45

Why is it especially good that the gut and kidney have increased resistance (vasoconstriction) during exercise?

Back 45

To maintain MAP - otherwise the massive dilation to exercising muscles would decrease MAP and you might faint or die.

Front 46

What is the effect of exercise on TPR?

Back 46

It is decreased

Front 47

Compare TPR at rest vs exercising:

Back 47

Resting: 100/5 = 20 TPR

Exercising: 120/20 = 6

TPR = MAP/CO

Front 48

How is TPR reduced during exercise?

Back 48

MAP is slightly increased and CO is markedly increased.