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)?

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

Question 1

Which phase of the cardiac muscle action potential is responsible for the plateau observed in the first image, and what ion movement primarily causes this plateau?

Accepted Answer

Phase 2; slow Ca2+ influx

Question 2

In the second image, the pacemaker potential is shown. What is the main reason the membrane potential never remains flat during the pacemaker potential?

Accepted Answer

Slow Na+ influx and closing of K+ channels

Question 3

Referencing the third image, which structure is the primary pacemaker of the heart, and what is its typical intrinsic firing rate?

Accepted Answer

Sinoatrial (SA) node; 75 beats/min

Question 4

In the fourth image, which nervous system division is responsible for decreasing heart rate, and through which nerve does it act?

Accepted Answer

Parasympathetic nervous system; vagus nerve

Question 5

In the fifth image, which wave corresponds to ventricular depolarization, and what is its physiological significance?

Accepted Answer

QRS complex; ventricular depolarization

Question 6

Based on the sixth image, what event immediately follows the QRS complex in the cardiac cycle?

Accepted Answer

Ventricular contraction (systole)

Question 7

In the seventh image, which ECG tracing is most consistent with ventricular fibrillation, and what is the clinical significance of this rhythm?

Accepted Answer

Bottom right; ventricular fibrillation

Question 8

Which of the following best describes the function of the AV node as shown in the conduction pathway images?

Accepted Answer

It delays the impulse to allow atrial contraction before ventricular contraction

Question 9

In the ninth image, which location is best for auscultating the mitral valve, and why is this clinically important?

Accepted Answer

Heart apex, 5th intercostal space in line with the middle of the clavicle; to detect mitral valve murmurs

Question 10

Which equation correctly represents cardiac output, and what are its components?

Accepted Answer

$$CO = HR 	imes SV$$

Question 11

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

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

Question 12

Which of the following would most likely increase cardiac output during exercise?

Accepted Answer

Increased sympathetic activity

Question 13

Which of the following best explains the Frank-Starling law of the heart?

Accepted Answer

The greater the stretch of cardiac muscle cells (preload), the greater the force of contraction

Question 14

Which of the following is a positive inotropic agent that increases contractility of the heart?

Accepted Answer

Epinephrine

Question 15

A patient with persistent high blood pressure is likely to experience which change in the heart's workload?

Accepted Answer

Increased afterload

Question 16

Which of the following best describes the effect of acetylcholine on pacemaker cells?

Accepted Answer

Hyperpolarizes pacemaker cells by opening K+ channels

Question 17

A 25-year-old athlete has a resting heart rate of 55 bpm. Which term best describes this condition, and what is its likely cause?

Accepted Answer

Bradycardia; increased vagal tone from endurance training

Question 18

Which congenital heart defect is characterized by a narrowed aorta, increasing the workload of the left ventricle?

Accepted Answer

Coarctation of the aorta

Question 19

Which of the following is a likely consequence of ventricular fibrillation if not treated promptly?

Accepted Answer

Cessation of effective circulation and death

The Cardiovascular System: The Heart – Structure, Function, and Physiology

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