Q: Which equation correctly represents cardiac output ($$CO) $$and its components?

$$CO = \text{stroke volume} \times \text{heart rate}$$

Q: A patient has a resting heart rate of 120 bpm and a stroke volume of 60 mL. What is their cardiac output ($$CO) in $$liters per minute?

$$CO = 120 \times 60 = 7200 mL/$$min $$= 7.2 L/$$min

Question 1

Which of the following best describes the primary function of intercalated discs in cardiac muscle tissue?

Accepted Answer

They provide electrical and mechanical coupling between cardiomyocytes, allowing synchronized contraction.

Question 2

A patient suffers a myocardial infarction that results in scar tissue formation in the left ventricle. Which of the following is the most likely consequence for electrical conduction in the affected area?

Accepted Answer

Electrical conduction will be impaired, potentially leading to arrhythmias.

Question 3

Which equation correctly represents cardiac output ($$CO) $$and its components?

Accepted Answer

$$CO = 	ext{stroke volume} 	imes 	ext{heart rate}$$

Question 4

During intense exercise, which of the following changes is most responsible for the increase in cardiac output?

Accepted Answer

A significant increase in heart rate, with stroke volume plateauing at high intensities.

Question 5

Which of the following best explains why the action potential in ventricular cardiomyocytes has a prolonged plateau phase?

Accepted Answer

It ensures sustained contraction for effective blood ejection and prevents tetanus.

Question 6

A patient has a resting heart rate of 120 bpm and a stroke volume of 60 mL. What is their cardiac output ($$CO) in $$liters per minute?

Accepted Answer

$$CO = 120 	imes 60 = 7200 mL/$$min $$= 7.2 L/$$min

Question 7

Which of the following is the primary reason for the delay of the electrical signal at the atrioventricular (AV) node?

Accepted Answer

To ensure the atria have time to fully contract and fill the ventricles before ventricular contraction.

Question 8

Which of the following best describes the effect of increased preload on stroke volume, according to the Frank-Starling law?

Accepted Answer

Increased preload increases stroke volume by stretching cardiomyocytes, leading to a stronger contraction.

Question 9

Which of the following ions is primarily responsible for the depolarization phase in pacemaker cells of the SA node?

Accepted Answer

Calcium ($$Ca^{2+}) $$influx through slow channels

Question 10

A patient with chronic hypertension has an aortic pressure of 115 mmHg. What is the minimum pressure the left ventricle must generate to open the aortic valve?

Accepted Answer

Greater than 115 mmHg

Question 11

Which of the following best explains why the right ventricle operates at a much lower pressure than the left ventricle?

Accepted Answer

The right ventricle pumps blood a shorter distance to the lungs, which have lower vascular resistance.

Question 12

Which of the following would most likely result from a complete (third-degree) bundle block in the heart?

Accepted Answer

The ventricles beat at their own intrinsic rate, independent of the atria.

Question 13

Which of the following best describes the effect of acetylcholine (ACh) released by the vagus nerve on the SA node?

Accepted Answer

It decreases the heart rate by hyperpolarizing pacemaker cells.

Question 14

Which of the following is the most likely effect of severe stenosis (narrowing) of the pulmonary trunk?

Accepted Answer

Systemic edema due to right heart failure.

Question 15

Which of the following best explains why endurance-trained athletes often have lower resting heart rates but higher stroke volumes?

Accepted Answer

Their hearts are more efficient, pumping more blood per beat, so fewer beats are needed to maintain cardiac output.

Question 16

Which of the following is the main reason why the heart cannot undergo tetanus (sustained contraction) like skeletal muscle?

Accepted Answer

The prolonged refractory period due to the plateau phase of the action potential prevents tetanus.

Question 17

Which of the following best describes the effect of increased afterload on stroke volume?

Accepted Answer

Increased afterload decreases stroke volume because the ventricle must work harder to open the semilunar valve.

Question 18

Which of the following best explains the role of baroreceptors in the regulation of cardiac output?

Accepted Answer

They detect changes in blood pressure and send feedback to the brainstem to adjust heart rate.

Question 19

Which of the following is the most likely effect of a loss of special cardiac macrophages that form gap junctions with AV node cells?

Accepted Answer

Progressive AV block due to impaired electrical coupling.

Cardiac Muscle and the Cardiac Conduction System: Structure and Function of Cardiomyocytes

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