Physiology of Vascular Tone and Blood Flow

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Questions and Answers

Which statement about blood flow regulation in skeletal muscles is true?

Vasodilation is inhibited by an increase in CO2 levels.

Oxidative fibers receive more blood flow due to their higher metabolic demands. (correct)

Blood flow primarily favors glycolytic fibers over oxidative fibers.

Vasoconstriction is mostly controlled by local metabolic factors.

What does the principle of 'functional sympatholysis' suggest?

Blood flow decreases in active muscles due to sympathetic stimulation.

Sympathetic nervous system activity is enhanced during high blood flow.

Nitric oxide secretion decreases with increased exercise intensity.

Local metabolic factors can override sympathetic vasoconstriction. (correct)

Which of the following metabolites is NOT associated with vasodilation in skeletal muscle?

Octopamine (correct)

Potassium ions

Adenosine

Nitric Oxide

How would an increase in blood flow influence nitric oxide release?

It would enhance nitric oxide secretion from the endothelium. Signup and view all the answers

What is the primary goal of extrinsic control of arteriolar tone?

To regulate mean arterial blood pressure. Signup and view all the answers

In terms of blood pressure, which of the following correctly describes diastolic blood pressure (DBP)?

It indicates systemic resistance in peripheral blood vessels. Signup and view all the answers

Which of the following factors would NOT cause vasodilation in skeletal muscle?

Increased norepinephrine activity Signup and view all the answers

Which mechanism primarily increases oxygen extraction from blood during exercise?

Enhanced offloading from hemoglobin due to the Bohr effect Signup and view all the answers

What is the primary effect of local vessels dilating in response to increased metabolites during exercise?

Increase in blood flow to active muscles Signup and view all the answers

During high-intensity exercise, the oxygen extraction (a-vO2 difference) can reach approximately what percentage?

90% Signup and view all the answers

How does blood flow redistribution occur during exercise?

Blood flow is substantially reduced away from the gut Signup and view all the answers

Which of the following statements about the cardiovascular response to exercise is incorrect?

Blood flow is mainly regulated by intrinsic control in all organs. Signup and view all the answers

What initiates the redistribution of blood flow in favor of active skeletal muscles during exercise?

Increase in local metabolites Signup and view all the answers

Which physiological response is primarily responsible for increased oxygen delivery to active muscles?

Greater proportion of cardiac output to muscles Signup and view all the answers

Which factor does NOT influence the regulation of vascular tone during exercise?

Ambient temperature Signup and view all the answers

Study Notes

Vascular Tone and Blood Flow

During exercise, active muscles have an increased oxygen demand.
This demand is met through four main mechanisms:
- Local vessel dilation due to increased metabolites
- Increased cardiac output (linear with work rate)
- Redistribution of blood flow to actively working muscles
- Increased oxygen extraction from each unit of blood (mainly intrinsic)
Increased oxygen extraction is achieved by:
- Redistribution of blood flow away from non-essential organs such as the gut, liver, and kidneys, while maintaining flow to the brain and heart.
- Increased metabolic activity in the muscle, leading to:
  - Bohr effect (increased oxygen unloading from hemoglobin)
  - Increased pressure gradient between blood and muscle, facilitating diffusion of oxygen

Intrinsic Control of Arteriolar Tone

Local factors released from tissues ensure perfusion (blood flow) meets metabolic demands.
Factors affecting arteriolar dilation:
- Temperature: Increased temperature causes dilation.
- Blood flow: Increased pressure or stretch causes dilation.
- Metabolites: Increased CO2, H+, K+, adenosine (especially in the heart), ATP, decreased PO2, and increased Nitric Oxide (NO) cause dilation.

Extrinsic Control of Arteriolar Tone

Extrinsic control maintains mean arterial pressure (MAP), primarily through the sympathetic nervous system (SNS).
The SNS releases norepinephrine, causing vasoconstriction.
Local metabolites can override SNS vasoconstriction, leading to ‘functional sympatholysis’ in active muscles.
This means the local vasodilatory effects are stronger than the vasoconstrictive effects of norepinephrine.

Blood Pressure

Blood pressure (BP) is determined by cardiac output multiplied by total peripheral resistance (Q x TPR).
Systolic blood pressure (SBP) estimates:
- The work performed by the heart
- The strain on arterial walls
- Overall cardiovascular function
Diastolic blood pressure (DBP) estimates peripheral resistance (TPR).
Mean arterial pressure (MAP) is calculated as: 2/3 DBP + 1/3 SBP

Blood Pressure Measurement

Learning to measure blood pressure accurately at rest and during exercise is essential for exercise physiologists.
Proper blood pressure measurement techniques are crucial for accurate assessment of cardiovascular function.

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Description

This quiz covers the mechanisms impacting vascular tone and blood flow during exercise, focusing on oxygen demand and delivery to muscles. Explore how local vessel dilation, cardiac output, and blood redistribution adapt to meet metabolic needs, including effects on arteriolar tone.