Q: A patient has an end-diastolic volume (EDV) of 120 mL and an end-systolic volume (ESV) of 50 mL. What is the stroke volume (SV)?

$$SV = EDV - ESV = 120\ \text{mL} - 50\ \text{mL} = 70\ \text{mL}$$

Question 1

Which of the following best describes the function of the SA node in the heart's conduction system?

Accepted Answer

It initiates the action potential that spreads throughout the heart, setting the pace for the heart rate.

Question 2

During the plateau phase (phase 2) of the cardiac contractile cell action potential, which ion movement is primarily responsible for maintaining the membrane potential?

Accepted Answer

Influx of Ca$$^{2+}$$ through voltage-gated Ca$$^{2+}$$ channels

Question 3

Which of the following is the correct formula for calculating cardiac output (CO)?

Accepted Answer

$$CO = HR 	imes SV$$

Question 4

A patient has an end-diastolic volume (EDV) of 120 mL and an end-systolic volume (ESV) of 50 mL. What is the stroke volume (SV)?

Accepted Answer

$$SV = EDV - ESV = 120\ 	ext{mL} - 50\ 	ext{mL} = 70\ 	ext{mL}$$

Question 5

Which event is represented by the QRS complex on an electrocardiogram (ECG)?

Accepted Answer

Ventricular depolarization

Question 6

What is the physiological significance of the long refractory period in cardiac muscle cells?

Accepted Answer

It prevents tetanus, ensuring the heart can relax and refill with blood between contractions.

Question 7

Which of the following would most likely result in an increased heart rate (positive chronotropic effect)?

Accepted Answer

Increased sympathetic stimulation releasing norepinephrine

Question 8

A drug that blocks voltage-gated Ca$$^{2+}$$ channels in cardiac contractile cells would have which of the following effects?

Accepted Answer

It would decrease the plateau phase, reducing the strength of contraction.

Question 9

According to the Frank-Starling law of the heart, an increase in venous return will have what effect on stroke volume?

Accepted Answer

Increase stroke volume due to greater stretch of ventricular muscle fibers

Question 10

Which of the following best describes the effect of acetylcholine (ACh) released by the parasympathetic nervous system on the heart?

Accepted Answer

ACh binds to muscarinic receptors on autorhythmic cells, slowing the rate of pacemaker depolarization and decreasing heart rate.

Question 11

A patient’s ECG shows a heart rate of 45 beats per minute with absent P waves and a regular rhythm. Which part of the conduction system is most likely acting as the pacemaker?

Accepted Answer

AV node

Question 12

Which of the following would increase cardiac contractility (positive inotropic effect)?

Accepted Answer

Increased release of epinephrine

Question 13

During which phase of the cardiac cycle do the AV valves close, producing the first heart sound ('lub')?

Accepted Answer

Early ventricular contraction (isovolumic contraction)

Question 14

Which of the following best explains why summation and tetanus do not occur in cardiac muscle?

Accepted Answer

The refractory period in cardiac muscle is as long as the muscle contraction.

Question 15

A patient is given a drug that increases the activity of phospholamban in cardiac muscle cells. What is the expected effect on cardiac muscle contraction?

Accepted Answer

Increased Ca$$^{2+}$$ reuptake into the sarcoplasmic reticulum, leading to shorter and more forceful contractions.

Question 16

Which of the following is the correct sequence of electrical conduction through the heart?

Accepted Answer

SA node → AV node → Bundle of His → Bundle branches → Purkinje fibers

Question 17

If a patient’s end-diastolic volume (EDV) is 140 mL, end-systolic volume (ESV) is 60 mL, and heart rate (HR) is 75 beats/min, what is the cardiac output (CO)?

Accepted Answer

$$CO = (EDV - ESV) 	imes HR = (140\ 	ext{mL} - 60\ 	ext{mL}) 	imes 75 = 6000\ 	ext{mL/min}$$

Question 18

Which of the following would most likely cause an increase in afterload?

Accepted Answer

Increased arterial blood pressure

Question 19

Which of the following best describes the effect of a positive inotropic agent on the heart?

Accepted Answer

It increases the force of contraction of the cardiac muscle.

Question 20

Which of the following mechanisms does NOT contribute to increased venous return?

Accepted Answer

Increased afterload

Cardiovascular Physiology: Electrical and Mechanical Events of the Heart

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