2.11A. Circulation of the skeletal muscle. Circulatory effects of physical exercise.

Question 1

Blood flow to the skeletal muscle is controlled by both ___ and ___

Answer 1

local metabolites and SYM innervation of its VSM

Question 2

I. Sympathetic innervation/stimuli
1. How is skeletal muscle circulation regulated by SYM innervation?

Answer 2

• At rest, skeletal muscle circulation is primarily regulated by SYM innervation
• VSMCs in arterioles of skeletal muscle have both
  1. α1 receptors: activated by NE and cause vasoconstriction
  2. β2 receptors: activated by E and cause vasodilation
  => vasoconstriction predominates because SYM adrenergic neurons stimulate primarily alpha1-AR
  => however, during the fight-or-flight response or exercise, E from the adrenal gland activates beta2-AR and causes vasodilation

Question 3

I. Sympathetic innervation/stimuli
2. What are the receptors you can find in skeletal muscle?

Answer 3

1. α1 receptors: activated by NE and cause vasoconstriction
2. β2 receptors: activated by E and cause vasodilation

Question 4

II. Local metabolites
1. How can local metabolites regulate skeletal muscle circulation?

Answer 4

• During exercise, local metabolites predominate the regulation of skeletal muscle circulation

Question 5

II. Local metabolites
2. What is Functional hyperemia?

Answer 5

an increase in perfusion to a tissue due to presence of metabolites

Question 6

II. Local metabolites
3B. What is relative hyperemia?

Answer 6

an increase in perfusion (vasodilation) following a short period of ischemia

Question 7

II. Local metabolites
3C. What is the mechanism of Functional hyperemia during regulation of Skeletal muscle circulation?

Answer 7

• Local metabolites trigger vasodilation in order to compensate: pO2↓, pCO2↑,
  [lactate]↑ (pH↓), [K+]↑, [adenosine]↑ - ATP metabolism
  => Exercise -> mechanical compression of the blood vessels, causing brief periods of occlusion, resulting in brief periods of reactive hyperemia to vasodilate and compensation

Question 8

III. What are the important parameters of Skeletal blood flow?

Answer 8

• Resting: 1L / min (20% of CO)
• At exercise: 20-30L/min (20-30x increase)
• AVDO2: (resting = 60 mL O2/L) (exercise = 150 mL O2/L)

Question 9

IV. Circulatory effects of physical exercise
1. How can dynamic exercise affect circulation of the skeletal muscle?

Answer 9

Dynamic exercise (such as running) is continuous contraction and relaxation and contraction again:
- during contraction, arterial inflow will be inhibited, during relaxation, arterial inflow will be increased
- venous outflow/return is increased by contraction (muscle pump)
- venous pressure will decrease with this mechanism, leads to increase of pressure gradient, which helps the blood flow

Question 10

IV. Circulatory effects of physical exercise
2. How can static exercise affect circulation of the skeletal muscle?

Answer 10

Static exercise (weightlifting), keeping the weight in one position when muscles are contracted:
- contraction -> resistance in vessels increase, decreased blood flow
- TPR significantly increases
- Leads to mean arterial blood pressure increase (systolic and diastolic pressure
increase)

Question 11

IV. regulation of skeletal muscle blood flow
1. What are the 2 types of regulation of skeletal muscle blood flow?

Answer 11

1. Local regulation: (most important)
2. Neurohumoral regulation: SYM innervation

Question 12

IV. regulation of skeletal muscle blood flow - Local regulation (most important)
2A. How is skeletal muscle blood flow regulated locally?

Answer 12

1. CO↑ (exercise)
2. Metabolic changes
3. From muscles

Question 13

IV. regulation of skeletal muscle blood flow - Local regulation (most important)
2B. How can CO↑ (exercise) participate in local regulation of skeletal muscle circulation?

Answer 13

CO↑ (exercise) -> metabolism ↑ + O2-consumption↑
-> Since ↑O2-consumption, we have different metabolic effects: pO2↓, pCO2↑, [H+]↑ (pH↓), [K+]↑, [adenosine]↑ - ATP metabolism
=> all lead to vasodilation

Question 14

IV. regulation of skeletal muscle blood flow - Local regulation (most important)
2C. How can Metabolic changes participate in local regulation of skeletal muscle circulation?

Answer 14

Metabolic changes
-> K+-channel activators (HCN, VDCC)
-> SM hyperpolarization
-> Ca2+-channel activation↓
-> [Ca2+]IC↓
-> vasodilation (relaxation)
- ↓[Ca2+] also comes from the increased cAMP due to adenosine

Question 15

IV. regulation of skeletal muscle blood flow - Local regulation (most important)
2D. How can MUSCLES participate in local regulation of skeletal muscle circulation?

Answer 15

From muscles
-> [Ca2+]↑, lead to NO synthase activation
-> NO (produced by
endothelial cells)
-> vascular SM relaxation
-> vasodilation

Question 16

IV. regulation of skeletal muscle blood flow
3. Describe Neurohumoral regulation

Answer 16

Neurohumoral regulation: SYM innervation
- Vessels have α1-AR -> constriction, β2-AR -> dilation
- α1 receptors: activated by NE and cause vasoconstriction
- β2 receptors: activated by E and cause vasodilation
- function: BP regulation