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How does the preload affect cardiac output?

A.

Decreased preload increases cardiac output.

B.

Increased preload decreases cardiac output.

C.

Increased preload increases cardiac output.

D.

Preload has no effect on cardiac output.

Answer and Explanation

The Correct Answer is C

A. Decreased preload increases cardiac output:
 Decreased preload reduces ventricular filling, leading to lower stroke volume and reduced cardiac output.

B. Increased preload decreases cardiac output:
 Increased preload generally increases stroke volume via the Frank-Starling mechanism, so it does not decrease cardiac output under normal physiological conditions.

C. Increased preload increases cardiac output:
 According to the Frank-Starling law, greater ventricular filling (preload) stretches cardiac fibers, resulting in a stronger contraction and higher stroke volume, thus increasing cardiac output.

D. Preload has no effect on cardiac output:
 Preload directly affects ventricular filling and stroke volume, which are critical determinants of cardiac output.


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Related Questions

Correct Answer is C

Explanation

A. To regulate heart rate:
Heart rate is controlled by the SA node and autonomic nervous system, not the pericardial sac.

B. To contract and assist with blood pumping:
The pericardium is non-contractile; it does not generate force to pump blood.

C. To provide a lubricated environment for the heart:
The pericardial sac contains pericardial fluid that reduces friction between the heart and surrounding structures during contraction and relaxation, protecting the heart from mechanical stress.

D. To store blood during diastole:
The pericardium does not store blood; ventricular chambers store blood transiently during diastole.

Correct Answer is B

Explanation

A. It regulates blood pressure:
Pericardial fluid does not directly regulate blood pressure. Blood pressure is controlled by cardiac output, vascular resistance, and fluid volume.

B. It reduces friction between the heart and surrounding tissues during contraction:
The pericardial sac contains pericardial fluid, which acts as a lubricant, allowing the heart to beat smoothly within the thoracic cavity. This prevents friction and mechanical injury to the heart and surrounding structures during systole and diastole.

C. It facilitates electrical conduction within the heart:
Electrical conduction is mediated by the SA node, AV node, bundle of His, and Purkinje fibers, not pericardial fluid.

D. It nourishes the heart muscle:
The myocardium is nourished by the coronary arteries, not by pericardial fluid.

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