Cardiovascular System Practice Questions

Q: Which ion is primarily responsible for initiating the action potential in contractile cardiac muscle cells (atrial and ventricular myocytes)?

Sodium (Na+). ***Sodium (Na+)*** - The rapid influx of **Na+ through fast voltage-gated sodium channels** is responsible for the rapid depolarization phase (Phase 0) of the action potential in contractile cardiac myocytes. - This initial influx quickly brings the membrane potential to a positive value, initiating the action potential. *Potassium (K+)* - While **K+ channels** are crucial for repolarization (Phase 3) and maintaining the resting membrane potential, they do not initiate the action potential. - An efflux of K+ ions causes the membrane potential to become more negative, leading to repolarization. *Calcium (Ca2+)* - **Ca2+ influx** through L-type calcium channels is responsible for the plateau phase (Phase 2) of the action potential, which prolongs the refractory period. - While important for excitation-contraction coupling, Ca2+ does not initiate the rapid depolarization phase. *Chloride (Cl-)* - **Chloride ions** play a more minor role in cardiac action potentials, primarily contributing to some repolarization currents but not to the initial depolarization. - Their primary role is in maintaining cellular osmolarity and charge balance.

Q: Immersion syndrome occurs due to ?

Vagal response to cold immersion. ***Vagal response to cold immersion*** - **Cold shock response** from sudden cold water exposure leads to an immediate gasp reflex, hyperventilation, and activation of the **parasympathetic nervous system** via the vagus nerve. - This vagal activation can cause **bradycardia**, arrhythmias, and even cardiac arrest in susceptible individuals. *Vagal stimulation during immersion* - While immersion can stimulate the vagus nerve, it is specifically the **cold temperature that triggers the significant vagal response** leading to immersion syndrome. - This option is too general and doesn't specify the crucial role of **cold** in initiating the syndrome. *Sympathetic response to cold immersion* - The initial response to cold immersion involves a rapid surge in **sympathetic activity**, leading to vasoconstriction and increased heart rate. - However, the dangerous cardiac events associated with immersion syndrome are predominantly mediated by the overwhelming **vagal (parasympathetic) response**, which can override the sympathetic drive. *Sympathetic inhibition during immersion* - Immersion, particularly into cold water, does not cause sympathetic inhibition; rather, it typically leads to an **initial sympathetic surge** as part of the body's stress response. - The critical cardiovascular risk is due to the subsequent strong **parasympathetic (vagal) activation**, not inhibition of the sympathetic system.

Q: What is the primary function of the M2 muscarinic receptor in the heart?

Causes hyperpolarization of the SA node. ***Causes hyperpolarization of the SA node*** - Activation of M2 receptors in the **sinoatrial (SA) node** leads to an increase in **potassium efflux**, causing the cell membrane to hyperpolarize. - This hyperpolarization makes it more difficult for the SA node cells to reach their threshold for depolarization, thereby **decreasing heart rate**. *Enhances contractility of the ventricles* - The M2 muscarinic receptor primarily mediates **parasympathetic effects**, which generally decrease cardiac function. - Enhancement of contractility is primarily mediated by **beta-1 adrenergic receptors** in the ventricles, part of the sympathetic nervous system. *Increases release of acetylcholine from nerve endings* - M2 receptors act as **autoreceptors** on presynaptic nerve terminals, and their activation typically **inhibits** further acetylcholine release. - This is a feedback mechanism to limit excessive parasympathetic stimulation. *Increases conduction velocity in the AV node* - Activation of M2 receptors in the **atrioventricular (AV) node** **decreases** conduction velocity, leading to a longer PR interval. - This effect contributes to the overall slowing of heart rate by delaying the impulse transmission to the ventricles.

Q: S2 is associated with ?

Closure of semilunar valves. ***Closure of semilunar valves*** - The **second heart sound (S2)** is produced by the simultaneous **closure of the aortic and pulmonic valves** at the end of ventricular systole. - This event marks the beginning of **ventricular diastole** and prevents blood from flowing back into the ventricles from the aorta and pulmonary artery. *Rapid ventricular filling* - This phase occurs during **diastole**, after the semilunar valves have closed and the AV valves have opened. - It is associated with the **third heart sound (S3)** if present, which is a low-frequency sound of rapid ventricular distention. *Atrial contraction* - **Atrial contraction** occurs late in ventricular diastole and precedes the first heart sound (S1). - It is sometimes associated with the **fourth heart sound (S4)** in cases of decreased ventricular compliance. *Closure of AV valves* - The **closure of the atrioventricular (AV) valves** (mitral and tricuspid) produces the **first heart sound (S1)**. - This event marks the beginning of **ventricular systole** and prevents blood from flowing back into the atria from the ventricles.

Q: What is the normal capillary wedge pressure?

5-10 mm Hg. ***5-10 mm Hg*** - The **pulmonary capillary wedge pressure (PCWP)** or **pulmonary artery occlusion pressure (PAOP)** reflects the pressure in the left atrium and, indirectly, the left ventricular end-diastolic pressure (LVEDP). - A normal PCWP range is typically **4-12 mm Hg**, with 5-10 mm Hg being a common, healthy average. *0-2 mm Hg* - This value is **too low** to represent a normal PCWP. - A PCWP this low could indicate **hypovolemia** or severe vasodilation. *15-20 mm Hg* - This value is **elevated** and suggests **left ventricular dysfunction**, **heart failure**, or **volume overload**. - It would indicate increased pressure in the pulmonary circulation, potentially leading to **pulmonary congestion**. *20-30 mm Hg* - These values are **markedly elevated** and are highly indicative of significant **left ventricular failure** and **pulmonary edema**. - Such high pressures reflect severe compromise of the heart's pumping ability.

Q: Dicrotic notch is caused by:

Closure of aortic valve. ***Closure of aortic valve*** - The **dicrotic notch**, also known as the incisura, represents a brief increase in aortic pressure as blood rebounds against the **closed aortic valve**. - This event marks the end of systole and the beginning of diastole in the arterial pressure waveform. *Opening of mitral valve* - The opening of the mitral valve occurs during early diastole and is associated with the **rapid filling of the left ventricle**, not a notch on the arterial pressure waveform. - This event is more relevant to changes in left ventricular and left atrial pressures. *Opening of aortic valve* - The opening of the aortic valve marks the beginning of **ventricular ejection** (systole) and the rapid upstroke of the arterial pressure wave. - It does not cause a notch in the descending limb of the arterial pressure waveform. *Closure of mitral valve* - The closure of the mitral valve occurs at the beginning of **ventricular systole** and is associated with the first heart sound (S1). - This event is primarily reflected in left ventricular pressure changes and does not directly cause the dicrotic notch on the arterial pressure wave.

Q: What is the correct order of blood flow velocity in the human circulatory system?

Aorta > Artery > Arteriole > Vein > Venule > Capillary. ***Aorta > Artery > Arteriole > Vein > Venule > Capillary*** - The **aorta** has the highest blood flow velocity (~30 cm/s) as it directly receives blood from the left ventricle - Blood velocity **progressively decreases** through arteries and arterioles as total cross-sectional area increases - **Capillaries have the LOWEST velocity** (~0.03 cm/s) due to their enormous total cross-sectional area (~2500 cm²), allowing optimal time for gas and nutrient exchange - Velocity **increases again** in venules and veins as vessels converge and total cross-sectional area decreases - The key principle: velocity is **inversely proportional** to total cross-sectional area of vessels *Vena cava > Aorta > Vein > Artery > Venule > Arteriole* - This sequence incorrectly places vena cava first when the **aorta has higher velocity** than vena cava - The mixed ordering doesn't follow the anatomical flow pathway *Aorta > Artery > Vena cava > Vein > Arteriole > Venule* - The vena cava is misplaced in this sequence - **Arterioles should have lower velocity than arteries** but higher than capillaries, not placed after veins *Vena cava > Vein > Capillary > Arteriole > Aorta > Artery* - This sequence is completely reversed - **Aorta and arteries have the highest velocities**, not the lowest - Capillaries have the **lowest velocity**, not in the middle of the sequence

Q: What is the resting membrane potential in ventricular cardiac muscle?

-90 mV. ***-90 mV*** - The resting membrane potential in **ventricular muscle fibers** is approximately **-90 mV**, due to the high permeability to **potassium ions** at rest. - This **polarized state** is maintained by the **Na+/K+ ATPase pump**, which establishes ion gradients. *-70 mV* - A resting membrane potential of **-70 mV** is characteristic of **neurons** and skeletal muscle cells, not typical cardiac muscle cells. - This value is mainly maintained by the differential distribution of **sodium** and **potassium ions**. *+70 mV* - A potential of **+70 mV** represents a **depolarized state** far from the resting potential, indicative of an action potential peak. - This value would signify an influx of **positive ions**, primarily sodium, into the cell during activation. *+90 mV* - A potential of **+90 mV** is also a **depolarized state** and is not a resting membrane potential for any excitable cell type. - This value would represent a significant influx of positive charge, causing cell excitation.

Q: The 'v' wave in JVP is due to:

Closure of tricuspid valve. ***Closure of tricuspid valve*** - The **'v' wave** in the JVP occurs during **ventricular systole** while the **tricuspid valve is closed**. - It represents the **passive filling of the right atrium** with venous return against the closed tricuspid valve, leading to a gradual rise in atrial pressure. - The peak of the 'v' wave occurs just before the tricuspid valve opens at the end of ventricular systole. - Note: The actual **closure** of the tricuspid valve produces the **'c' wave**, while the 'v' wave reflects the consequences of the valve remaining closed during atrial filling. *Right atrial contraction* - **Right atrial contraction** causes the **'a' wave** in the JVP, which is the first positive deflection in the cardiac cycle. - This wave reflects the increase in right atrial pressure as the atrium contracts to propel blood into the right ventricle during late diastole. *Isovolumetric relaxation* - **Isovolumetric relaxation** of the ventricle occurs after semilunar valve closure and before the tricuspid valve opens. - This phase is associated with the **'y' descent**, as ventricular pressure falls below atrial pressure allowing the tricuspid valve to open and blood to flow rapidly into the ventricle. *Right atrial relaxation* - **Right atrial relaxation** follows atrial contraction and contributes to the **'x' descent** in the JVP. - This decline reflects the pressure drop in the right atrium as it relaxes after contraction, coinciding with ventricular systole pulling the tricuspid annulus downward.

Q: What is the average blood supply to the brain in ml/min?

750 ml/min. ***750 ml/min*** - The brain receives approximately **15% of the total cardiac output**, which translates to about 750 ml of blood per minute in a resting adult. - This flow rate is crucial for supplying the brain with adequate **oxygen and nutrients** to maintain its high metabolic demand. *1500 ml/min* - This value is significantly higher than the average blood flow to the brain and would represent an **abnormally increased cerebral blood flow**, potentially seen in specific pathological states. - The brain's metabolic needs, while substantial, do not typically require such a large volume of blood per minute under normal physiological conditions. *2000 ml/min* - This is an **extremely high value** for cerebral blood flow and is not consistent with normal physiological measurements for an adult brain. - Such a high flow rate could lead to **vascular issues** or is indicative of specific disease states rather than normal function. *250 ml/min* - This value represents a **significantly reduced cerebral blood flow**, which would be insufficient to meet the metabolic demands of the brain. - A persistent flow rate this low would likely result in **ischemia** and neuronal damage.

Question 1

Which ion is primarily responsible for initiating the action potential in contractile cardiac muscle cells (atrial and ventricular myocytes)?

Accepted Answer

Sodium (Na+)

Answer

Calcium (Ca2+)

Answer

Chloride (Cl-)

Answer

Potassium (K+)

Question 2

Immersion syndrome occurs due to ?

Accepted Answer

Vagal response to cold immersion

Answer

Vagal stimulation during immersion

Answer

Sympathetic response to cold immersion

Answer

Sympathetic inhibition during immersion

Question 3

What is the primary function of the M2 muscarinic receptor in the heart?

Accepted Answer

Causes hyperpolarization of the SA node

Answer

Enhances contractility of the ventricles

Answer

Increases release of acetylcholine from nerve endings

Answer

Increases conduction velocity in the AV node

Question 4

S2 is associated with ?

Accepted Answer

Closure of semilunar valves

Answer

Rapid ventricular filling

Answer

Atrial contraction

Answer

Closure of AV valves

Question 5

What is the normal capillary wedge pressure?

Accepted Answer

5-10 mm Hg

Answer

0-2 mm Hg

Answer

15-20 mm Hg

Answer

20-30 mm Hg

Question 6

Dicrotic notch is caused by:

Accepted Answer

Closure of aortic valve

Answer

Opening of aortic valve

Answer

Opening of mitral valve

Answer

Closure of mitral valve

Question 7

What is the correct order of blood flow velocity in the human circulatory system?

Accepted Answer

Aorta > Artery > Arteriole > Vein > Venule > Capillary

Answer

Vena cava > Aorta > Vein > Artery > Venule > Arteriole

Answer

Aorta > Artery > Vena cava > Vein > Arteriole > Venule

Answer

Vena cava > Vein > Capillary > Arteriole > Aorta > Artery

Question 8

What is the resting membrane potential in ventricular cardiac muscle?

Accepted Answer

-90 mV

Answer

-70 mV

Answer

+70 mV

Answer

+90 mV

Question 9

The 'v' wave in JVP is due to:

Accepted Answer

Closure of tricuspid valve

Answer

Isovolumetric relaxation

Answer

Right atrial relaxation

Answer

Right atrial contraction

Question 10

What is the average blood supply to the brain in ml/min?

Accepted Answer

750 ml/min

Answer

1500 ml/min

Answer

2000 ml/min

Answer

250 ml/min

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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