Q: Which ion channel is primarily responsible for the pacemaker potential in SA node cells, and what is its main effect?

HCN channel; slow Na$^{+}$ influx causing gradual depolarization

Q: A 25-year-old athlete has a resting heart rate of 50 bpm and a stroke volume of 110 mL/beat. What is her cardiac output at rest?

$CO = 50 \times 110 = 5500\ \text{mL/min} = 5.5\ \text{L/min}$

Q: If a person has an end-diastolic volume (EDV) of 130 mL and an end-systolic volume (ESV) of 60 mL, what is their stroke volume (SV)?

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

Question 1

Which of the following best describes the function of the atrioventricular (AV) node in the cardiac conduction system?

Accepted Answer

It delays the impulse to allow the atria to finish contracting before the ventricles start.

Question 2

A patient presents with a heart rate of 45 bpm and an ECG showing absent P waves but normal QRS complexes. Which structure is most likely acting as the pacemaker in this scenario?

Accepted Answer

Atrioventricular (AV) node

Question 3

Which ion channel is primarily responsible for the pacemaker potential in SA node cells, and what is its main effect?

Accepted Answer

HCN channel; slow Na$^{+}$ influx causing gradual depolarization

Question 4

Which of the following equations correctly represents cardiac output (CO)?

Accepted Answer

$CO = HR 	imes SV$

Question 5

According to the Frank-Starling Law of the Heart, which of the following statements is correct?

Accepted Answer

The strength of ventricular contraction increases as end-diastolic volume (EDV) increases.

Question 6

A 25-year-old athlete has a resting heart rate of 50 bpm and a stroke volume of 110 mL/beat. What is her cardiac output at rest?

Accepted Answer

$CO = 50 	imes 110 = 5500\ 	ext{mL/min} = 5.5\ 	ext{L/min}$

Question 7

Which of the following best explains why athletes have a lower resting heart rate compared to non-athletes?

Accepted Answer

They have a higher stroke volume, so the heart does not need to beat as often to maintain cardiac output.

Question 8

Which of the following is a direct effect of sympathetic stimulation on the heart?

Accepted Answer

Increased contractility (positive inotropic effect)

Question 9

A patient with severe hypoalbuminemia develops edema. Which mechanism best explains this finding?

Accepted Answer

Decreased plasma oncotic pressure allows fluid to accumulate in the interstitial space.

Question 10

Which of the following best summarizes the body's dynamic equilibrium for blood volume regulation?

Accepted Answer

Blood volume is regulated through urine output, drinking, sweating, and breathing.

Question 11

During the cardiac cycle, which event immediately follows ventricular depolarization?

Accepted Answer

Ventricular contraction (systole)

Question 12

Which of the following is a likely finding on an ECG in a patient with a bundle branch block?

Accepted Answer

Widened QRS complex

Question 13

If a person has an end-diastolic volume (EDV) of 130 mL and an end-systolic volume (ESV) of 60 mL, what is their stroke volume (SV)?

Accepted Answer

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

Question 14

Which of the following best describes the effect of acetylcholine on the SA node?

Accepted Answer

It decreases heart rate by opening K$^{+}$ channels.

Question 15

A patient with a heart attack is found to have abnormal Q waves on ECG. What does this most likely indicate?

Accepted Answer

Previous myocardial infarction with necrotic tissue

Question 16

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

Accepted Answer

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

Question 17

Which of the following best explains why capillary permeability increases during allergic reactions, leading to edema?

Accepted Answer

Proteins escape into the interstitial space, reducing plasma oncotic pressure.

Question 18

Which of the following statements about total body water (TBW) is correct?

Accepted Answer

Extracellular fluid (ECF) makes up about 1/3 of TBW.

Question 19

A patient with a parasitic infection develops lymphatic obstruction. What is the most likely consequence?

Accepted Answer

Edema due to impaired lymphatic drainage

Question 20

Which of the following best describes the effect of increased end-diastolic volume (EDV) on stroke volume (SV), according to the Frank-Starling mechanism?

Accepted Answer

Increased EDV leads to increased SV.

P: Cardiovascular System 6

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