Lecture 21 (Part 2): Skeletal Muscle Blood Flow

Question 1

How does exercising muscle blood flow and O2 consumption differ from rest values?

Answer 1

BF: 2-4 ml.min.100g –> 250ml.min.100g

O2 consumption: 2-4ml.min –> 3.9L.min

Question 2

Describe the increase of muscle blood flow during dynamic exercise.

Answer 2

Onset: massive increase in skeletal muscle blood flow (by 7 seconds)
Plateaus
Another more gradual rise at 20 seconds.
Steady state reached at about a minute.

Question 3

Are there any neural influences on the rapid rise in BF at the onset of exercise?

Answer 3

No.

Question 4

What mechanical factor increases blood flow slightly at the onset of exercise and how does it work?

Answer 4

Skeletal muscle pump.
Increases venous return via mechanical compression and then relaxation.
This increases blood flow, but only has a small part to play at the onset of exercise.

Question 5

How do metabolites cause an increase in blood flow?

Answer 5

Increased metabolite production by muscle cells.

Stimulation of vasodilation to flush out metabolites.

Question 6

Are increases in potassium the reason for the increase in blood flow at the onset of exercise?

Answer 6

Probably not, as potassium levels didn’t rise quick enough in humans.
Took 1 minute to rise.

Question 7

What is the criteria for a metabolite that increases blood flow at the onset of exercise?

Answer 7

Vasodilator.
Increases in large quantities.
Fits time scale as an onset vasodilator.
Inhibition decreases blood flow at exercise onset.

Question 8

Name 6 vasodilator factors.

Answer 8

Hypoxia
Acidosis 
Osmolarity
Lactate 
Potassium 
Adenosine

Question 9

Does adenosine fit the criteria as a vasodilator for exercise onset increases in muscle blood flow?

Answer 9

Yes, as it increases a lot at the onset of exercise.

Although when blocked, there is still some hyperaemia therefore it is not the only metabolite causing vasodilation.

Question 10

Name two endothelium derived relaxation factors (EDRF’s).

Answer 10

Nitric Oxide and Prostaglandins

Question 11

Where is nitric oxide most important in blood flow response to exercise?

Answer 11

Contributes to 35% of the recovery stage after exercise (satisfying oxygen debt)

Question 12

What is exercise hyperaemia?

Answer 12

Increased arterial blood volume due to exercise

Question 13

Despite lowering blood pressure via vasodilation during exercise, why do we still need to maintain some vasoconstriction?

Answer 13

To determine direction of blood flow and regulate blood pressure

Question 14

What is functional sympatholysis?

Answer 14

Vasodilatory factors have to overcome vasoconstricting factors.
E.g. inhibition of noreadrenaline on alpha 2 receptors.