Circulatory Responses to Exercise

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Questions and Answers

What is the formula for calculating Cardiac Output (Q)?

Q = stroke volume (SV) + heart rate (HR)

Q = heart rate (HR) x stroke volume (SV) (correct)

Q = heart rate (HR) - stroke volume (SV)

Q = total volume pumped x time

Which system primarily regulates a decrease in heart rate?

Parasympathetic nervous system (correct)

Endocrine system

Central nervous system

Sympathetic nervous system

What is the effect of the skeletal muscle pump during exercise?

It directly pumps blood away from the heart.

It relaxes the blood vessels, reducing blood flow.

It decreases venous return to the heart.

It increases the amount of venous blood returning to the heart. (correct)

How does increased End Diastolic Volume (EDV) affect Stroke Volume (SV)?

Increases the stretch of ventricular sarcomeres, enhancing contraction force. Signup and view all the answers

What effect does the sympathetic nervous system have on heart rate?

It increases heart rate by stimulating the SA and AV nodes. Signup and view all the answers

What physiological principle does the Frank-Starling mechanism describe?

Force of contraction is proportional to fiber length. Signup and view all the answers

During exercise, how does cardiac output change in untrained individuals compared to highly trained athletes?

Highly trained athletes can increase cardiac output to about 35 l/min. Signup and view all the answers

What is a major factor contributing to increased end-diastolic volume (EDV)?

Enhanced sympathetic stimulation of peripheral veins. Signup and view all the answers

At what percentage of VO2 max does stroke volume typically plateau during exercise?

40% Signup and view all the answers

Which factor does NOT contribute to increased oxygen delivery to skeletal muscle during exercise?

Increased blood volume. Signup and view all the answers

What is 'cardiac drift' observed during prolonged exercise?

Decrease in venous return during prolonged exercise. Signup and view all the answers

How is maximum heart rate typically calculated?

220 - age (years) Signup and view all the answers

Which statement best describes the relationship between heart rate and cardiac output during exercise?

At higher exercise intensities, heart rate is the only determinant of cardiac output. Signup and view all the answers

What is one primary function of the circulatory system?

Protection against pathogens Signup and view all the answers

Which component of the circulatory system acts as a pump?

The heart Signup and view all the answers

What characteristic defines arterioles in the circulatory system?

They are known as 'resistance vessels' Signup and view all the answers

What triggers vasodilation during exercise?

Increased levels of potassium ions Signup and view all the answers

Which vessel contains the majority of the total blood volume?

Vein Signup and view all the answers

What is a potential physiological mechanism to overcome postural hypotension?

Increment in heart rate Signup and view all the answers

Which statement about blood vessels is true?

Arteries have thicker walls than veins Signup and view all the answers

What role does plasma play in blood composition?

It makes up about 56% of total blood volume Signup and view all the answers

Study Notes

Circulatory Responses to Exercise

The cardiovascular (CV) system has several key functions including delivery, transport, maintenance, and removal of substances. Protection is also involved.
The CV system consists of a fluid medium (blood), a network of channels (blood vessels), and a pump (the heart).
Blood is composed of 55% plasma (90% water, 7% plasma proteins, 3% other), and 45% formed elements (predominantly red blood cells). The vascular system has varying vessel structures, including the aorta, arteries, arterioles, capillaries, venules, and veins. The vena cava is a large vein.
The heart acts as two pumps in one, working in tandem for pulmonary and systemic circulation.
The heart has specific structures like atria, ventricles, valves, and septa, for effective blood flow.
Endurance training can cause changes in plasma volume and red blood cell percentage, impacting the overall composition of blood.
Blood vessel structure varies based on their function and location in the body. For example, Capillaries have very thin walls allowing for the exchange of materials.
Arterioles are resistance vessels, regulating blood flow to different parts of the body using intrinsic and extrinsic mechanisms. Intrinsic mechanisms adjust blood flow by factors like O2, CO2, H+, and K+. Extrinsic controls involve the sympathetic nervous system adjusting blood flow via hormones like adrenaline and noradrenaline.
Blood flow is redistributed during exercise, shifting towards the exercising muscles and away from less active organs.
Venous system (capacitance vessels) are important for accommodating blood volume changes without dramatic pressure changes.
Venous return is aided by venous valves and skeletal muscle pumps.

Cardiac Output

Cardiac output (Q) is the amount of blood pumped by the heart per minute (L/min). It is calculated as heart rate (HR) multiplied by stroke volume (SV).
Stroke volume (SV) is the amount of blood ejected by the ventricles with each beat (ml).
End-diastolic volume (EDV) and end-systolic volume (ESV) are factors contributing to SV.

Regulation of Heart Rate

Heart rate is adjusted by the autonomic nervous system, with parasympathetic nerves slowing it and sympathetic nerves increasing it. Resting heart rate is relatively low due to parasympathetic tone, but increases significantly at the onset of exercise. This initial increase is due to the withdrawal of parasympathetic impulses. Further increase in rate comes from increasing sympathetic activity.

Factors Affecting Stroke Volume

Stroke volume is influenced by the force of contraction and end-diastolic volume (EDV). Increased sympathetic nervous system activation increases force of contraction from circulating adrenaline and noradrenaline. The increase in EDV occurs via a length-tension relationship in the heart muscle. Training can impact left ventricular (LV) compliance, further affecting SV.

EDV - The Frank-Starling Mechanism

The Frank-Starling mechanism: The force of contraction is directly proportional to the fibre length of heart muscle. Increased EDV stretches the heart muscle fibers, potentially increasing the force of contraction and subsequently SV.

Major Factors Affecting EDV

Increased sympathetic activity to veins and blood volume, skeletal muscle pump, and increased inspiration affect venous return. These factors increase venous pressure, enhancing atrial pressure and ventricular EDV, leading to a subsequent increase in stroke volume.

Changes in Cardiac Output During Exercise

Cardiac output increases due to increases in both heart rate (HR) and stroke volume (SV) initially. HR increases linearly until maximal heart rate is achieved. SV also increases then plateaus at approximately 40% VO2 max.
Highly trained endurance athletes can substantially increase cardiac output beyond untrained individuals.

Transition from Rest to Submaximal Exercise to Recovery

During exercise, cardiac output, heart rate, and stroke volume increase. During recovery, these parameters return gradually to baseline

Cardiovascular Changes During Prolonged Exercise

During prolonged exercise, cardiac output remains relatively stable but cardiac drift occurs. Cardiac drift is an upward trend in heart rate over time. Stroke volume naturally decreases. Venous return also decreases.

Summary: Circulatory Adjustments With Exercise

Oxygen delivery to exercising skeletal muscles occurs through increased cardiac output via redistribution from inactive to working tissues.
Cardiac output rises with exercise as a linear function of oxygen uptake. SV plateaus at approximately 40% VO2 max. Sustained increased activity in cardiac output occurs due to increases in heart rate alone beyond this threshold.