heart- practice questions (b2- CVS)

Question 1

The Frank-Starling mechanism of the heart implies that:

Answer 1

Greater venous return increases stroke volume

Question 2

Frank-Starling law

Answer 2

Frank-Starling law states that the more the cardiac muscle is stretched (i.e., greater end-diastolic volume) = stronger the force of contraction, resulting in increased stroke volume.

• This is intrinsic regulation, independent of external nerves or hormones

Question 3

Which of the following is NOT an intrinsic regulator of the heart’s pumping action?

Answer 3

Sympathetic nervous stimulation

its an extrinsic factor

Question 4

What is the primary effect of the Bainbridge reflex on heart function?

Answer 4

Increase in heart rate

Bainbridge reflex is triggered when stretch receptors in the right atrium sense increased venous return (e.g., after IV infusion)

increased venous return → stimulation of stretch receptors in right atrium → afferent impulses through inferior cervical sympathetic nerve → inhibition of vasodilator area → decrease in vagal tone → tachycardia

Question 5

why does increase in body temp raise heart rate?

Answer 5

increase in body temperature leads to increased metabolic activity of cardiac pacemaker cells, especially the SA node.

This raises the rate of depolarization, resulting in an increased heart rate (positive chronotropic effect).

Fever is a clinical example where tachycardia is commonly observed

Question 6

What is the primary effect of increased extracellular calcium ions on the cardiac muscle?

Answer 6

Increased force of contraction

Increased extracellular Ca²⁺ = more Ca²⁺ influx during plateau phase cardiac AP = enhanced Ca²⁺-induced Ca²⁺ release from the sarcoplasmic reticulum = stronger contraction (positive inotropic effect)

Question 7

Which autonomic effect increases both the rate and force of cardiac contraction?

Answer 7

Sympathetic stimulation via β1-receptors

sympathetic nerves release norepinephrine, which binds β1-adrenergic receptors, leading to increased HR (chronotropy) and increased contractility (inotropy)

Question 8

Which phase of the cardiac cycle is shortened most by sympathetic stimulation?

Answer 8

diastole

during sympathetic stimulation, heart rate increases, primarily by shortening diastole (filling phase). However, stroke volume is preserved due to enhanced contractility.

Question 9

Which of the following best describes the effect of severe hyperkalemia on the electrical activity of the heart?

Answer 9

Inactivation of Na⁺ channels leading to bradycardia and possible cardiac arrest

severe hyperkalemia = high extracellular K⁺ = persistent depolarization of cardiac cell membrane = inactivation of voltage-gated Na⁺ channels = slowed conduction, reduced pacemaker activity = bradycardia, and in extreme cases = cardiac arrest, particularly by asystole or ventricular fibrillation

Question 10

Which of the following increases stroke volume by positive inotropy (increased strength/contractility of the heart)?

Answer 10

Norepinephrine acting on cardiac myocytes

Norepinephrine enhances calcium influx = increasing contractility (positive inotropy), = stronger contraction and higher stroke volume

Question 11

Q10. Which of the following best explains how hyperthermia affects the stroke volume and cardiac output?

Answer 11

Stroke volume decreases; cardiac output increases

In hyperthermia, HR increases significantly due to sympathetic stimulation, but stroke volume may decrease slightly due to reduced filling time

However, because cardiac output = heart rate × stroke volume, the overall cardiac output increases. The body compensates to maintain perfusion, especially during heat stress or fever.

Question 12

A patient has increased venous return. What is the first physiological response that increases cardiac output?

Answer 12

Frank Starling mechanism

The first, immediate response to increased venous return is the stretching of myocardial fibers, causing a stronger contraction and thus increased stroke volume—all intrinsic

Question 13

During intense sympathetic stimulation, the heart may beat up to 180 bpm. Why does stroke volume not drastically fall despite shorter filling time?

Answer 13

Contractility is greatly enhanced

Though diastolic time shortens, sympathetic inotropic effect (via increased Ca²⁺ availability) enhances ejection efficiency, partially compensating for reduced preload

Question 14

Q13. A 25-year-old athlete is running a marathon in hot weather. As his core temperature rises, which of the following molecular mechanisms most directly contributes to the increase in heart rate?

Answer 14

Increased activity of HCN (funny) channels in pacemaker cells

Elevated temperature increases the rate of spontaneous depolarization in pacemaker cells, partly through increased activity of HCN (“funny”) channels, which are activated by hyperpolarization and regulated by cAMP. These channels carry an inward Na⁺ current that contributes to the pacemaker potential. Temperature-induced sympathetic stimulation also raises intracellular cAMP, further enhancing HCN activity, leading to faster heart rate.

Question 15

A drug inhibits L-type calcium channels in cardiac myocytes. Which of the following effects is most likely?

Answer 15

Reduced force of ventricular contraction

L-type calcium channels are responsible for calcium influx during the plateau phase in ventricular myocytes. Blocking these channels leads to reduced intracellular Ca²⁺, which decreases calcium-induced calcium release from the sarcoplasmic reticulum. This results in a decrease in myocardial contractility, particularly in ventricular muscle. This is the basis for the use of calcium channel blockers in hypertension and angina.

Question 16

In a healthy person lying down, an infusion of saline leads to increased venous return and triggers the Bainbridge reflex. Which of the following accurately describes the expected integrated cardiovascular response?

Answer 16

Tachycardia with increased cardiac output

Saline infusion increases venous return, stretching the right atrium and activating the Bainbridge reflex, which causes tachycardia. This increases cardiac output to prevent blood pooling and maintain homeostasis. This response works in parallel with the Frank-Starling mechanism, ensuring that both heart rate and stroke volume adapt to increased preload

Question 17

bainbridge reflex/atrial reflex

Answer 17

cardiovascular reflex that causes an increase in heart rate in response to stretching of the right atrium and/or inferior vena cava due to increased venous filling

Question 18

What is the total time from SA node to complete ventricular depolarization?

Answer 18

0.36 to 0.43 seconds

Question 19

How fast is conduction in Purkinje fibers?

Answer 19

Very fast: 2–4 m/s

Question 20

What is the PR interval time on ECG, and what does it represent?

Answer 20

0.12–0.20 seconds, representing time from atrial depolarization to ventricular depolarization

Question 21

How long is the total AV nodal delay?

Answer 21

About 0.13 seconds (0.09 sec in AV node + 0.04 sec in AV bundle).

Question 22

What is the primary role of the AV node in cardiac impulse propagation?

Answer 22

To delay the impulse, allowing the atria to contract before the ventricles

Question 23

Which part of the cardiac conduction system ensures rapid and synchronized contraction of the ventricles?

Answer 23

Purkinje fibers

Question 24

What are the effects of sympathetic stimulation on the heart?

Answer 24

↑ Chronotropy: ↑ Heart rate
↑ Dromotropy: ↑ Conduction speed
↑ Inotropy: ↑ Contractility (force)

Question 25

What are the effects of parasympathetic stimulation on the heart?

Answer 25

↓ Chronotropy: ↓ Heart rate ↓ Dromotropy: ↓ Conduction velocity

Question 26

What is the mechanism of parasympathetic stimulation?

Answer 26

Acetylcholine binds to **M2 receptors** **Opens K⁺ channels** → hyperpolarization ↓ cAMP → **Slower opening of L- and T-type Ca²⁺ channels**

Question 27

whats the difference between cardiac output and stroke volume?

Answer 27

**stroke volume**: amount of blood pumped out by one ventricle in one heartbeat - typically *~70 mL/beat (in a healthy adult at rest)* - depends on: *preload (venous return), contractility (strength of heart muscle contraction), afterload (resistance in arteries)* **cardiac output**: total amount of blood pumped by one ventricle in one minute **formula: cardiac output = stroke volume x heart rate**

Question 28

1st, 2nd, 3rd heart sounds

Answer 28

**1st**: closure of aortic and pulmonary valves **2nd**: closure of AV valves (mitral & tricuspid) **3rd**: during ventricular filling; blood comes in so fast that vibrations of the ventricular walls makes this sound after enough blood has entered the ventricular chambers

Question 29

In which phase of the ventricular muscle action potential is the potassium permeability the highest?

Answer 29

phase 3

Question 30

typical ejection fraction in resting adult

Answer 30

**60%** *anything lower indicates weakened heart*

Question 31

stroke volume formula

Answer 31

stroke volume = ejection fraction x end diastolic volume

Question 32

end diastolic volume is always ________ than end systolic volume

Answer 32

greater

Question 33

heart rate formula using time b/w R-R interval

Answer 33

60/time b/w R-R interval *ex. time is 0.2 sec so 60/0.2*

Question 34

Which of the following is most likely to cause the heart to go into spastic contraction?

Answer 34

excess extracellular fluid calcium ions

Question 35

Which of the following events occurs at the end of the period of ventricular ejection?

Answer 35

At the end of ventricular ejection, **both the aortic valves and the pulmonary valves close**. This is followed by the period of isovolumic relaxation.

Question 36

Which of the following phases of the cardiac cycle follows immediately after the beginning of the QRS wave?

Answer 36

Immediately after the QRS wave, the **ventricles begin to contract** and the first phase that occurs is **isovolumetric contraction**. This occurs **before the ejection phase** and **increases the ventricular pressure enough to mechanically open** the aortic and pulmonary valves.

Question 37

Which of the following conditions will result in a **dilated, flaccid and slowed** heart?

Answer 37

**excess K+ ions in the blood** causes the cardiac resting membrane to become more positive and as it becomes more positive, intensity of the action potential decreases which makes heart progressively weaker

Question 38

How will increase in Na+ permeability affect the AV node?

Answer 38

they will **partially depolarize it**

Question 39

how does sympathetic stimulation affect the heart?

Answer 39

- increases heart rate - increases atrial & ventricular contractility - increases norepinephrine release at ventricular sympathetic nerve endings - upward drift of resting membrane potential of the SA node

Question 40

What is the normal total delay of the cardiac impulse in the A-V node plus bundle?

Answer 40

0.13 sec

Question 41

Which of the following structures will have the slowest rate of conduction of the cardiac action potential?

Answer 41

**AV bundle fibers** *partly caused by reduced # of gap junctions b/w muscle cells in the conducting pathway = more resistance to conduction of excitatory ions from one cell to the next*

Question 42

If the S-A node discharges at 0.00 seconds, when will the action potential normally arrive at the epicardial surface at the **base of the left ventricle**?

Answer 42

0.22 sec

Question 43

If the S-A node discharges at 0.00 seconds, when will the action potential normally arrive at the **A-V bundle (bundle of His)**?

Answer 43

0.12 sec

Question 44

Which of the following conditions at the S-A node will cause heart rate to decrease?

Answer 44

**increased K+ permeability** *causes hyperpolarization of the SA node causing heart rate to decrease*

Question 45

Which of the following are caused by acetylcholine?

Answer 45

hyper polarization of the SA node

Question 46

What is the membrane potential (threshold level) at which the S-A node discharges?

Answer 46

-40 mV

Question 47

intrinsic rhythmical rate of AV node & purkinje fibers

Answer 47

**AV node**: 40-60 bpm **purkinje fibers**: 30 bpm

Question 48

2 differences b/w the sinus nodal fibers & the ventricular muscle fibers

Answer 48

1. resting membrane potential of **sinus nodal fibers is -55 mV** 2. Sinus fibers exhibit **self-excitation** from inward leaking of Na+ ions

Question 49

When recording **lead I** on an EKG, the right arm is the negative electrode, and the positive electrode is the

Answer 49

**left arm** cause its basically a straight line across the x axis

Question 50

When recording **lead aVL** on an EKG, the positive electrode is the

Answer 50

**left arm**

Question 51

how many seconds is each small sq in an EKG? `

Answer 51

0.04 sec

Question 52

what is the time duration of the normal QT interval?

Answer 52

0.35 secs

Question 53

When recording **lead II** on an EKG, the positive electrode is the

Answer 53

left leg

Question 54

Einthoven's law

Answer 54

voltage in lead I + lead III = voltage in lead II **Lead I + Lead III = Lead II**

Question 55

normal mean electrical axis of heart typically falls in what range

Answer 55

-30 and +90 degrees

Question 56

Which of the following conditions will usually result in right axis deviation in an EKG?

Answer 56

pulmonary hypertension

Question 57

EKG has no P waves and a low heart rate, likely diagnosis?

Answer 57

**sinoatrial block** impulse leaving the sinus node is totally blocked before entering the atrial muscle

Question 58

Which of the following statements are likely conditions in someone with atrial fibrillation?

Answer 58

**rate of ventricular contraction is irregular and fast** *atrial fibrillation = rapid irregular heart rate* P waves are missing or are very weak

Question 59

Circus movements in the ventricle can lead to ventricular fibrillation. Which of the following conditions in the ventricular muscle will increase the tendency for circus movements?

Answer 59

**Decreased refractory period** circa movements occur in ventricular muscle if you have a dilated heart or decreases in conduction velocity - *high extracellular K+ & sympathetic stimulation increase tendency for circus movements*