Cardiovascular System — MCQs

A 75-year-old woman is admitted to the hospital with anginal pain. The ECG reveals myocardial infarction and a right bundle branch block. During physical examination, the patient has a loud second heart sound. Which of the following heart valves are responsible for the production of the second heart sound?

Q918

TGF-β is involved in all of the following processes of angiogenesis, except:

Q919

The organ with maximum blood flow in milliliters per kilogram per minute during resting is:

Q920

In the context of hypoxia, the cardiovascular response to peripheral chemoreceptor stimulation can result in which of the following changes in heart rate?

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 911: Mean arterial pressure depends on which of the following?

A. Cardiac output
B. Cardiac output & peripheral resistance (Correct Answer)
C. Peripheral resistance
D. Arterial compliance

Explanation: ***Cardiac output & peripheral resistance*** - **Mean arterial pressure (MAP)** is determined by the fundamental relationship: **MAP = Cardiac Output (CO) × Systemic Vascular Resistance (SVR)** - Both factors are **equally essential** - MAP cannot be determined by either factor alone - Changes in either CO or peripheral resistance will directly affect MAP - This represents the primary hemodynamic determinants of arterial pressure *Cardiac output alone* - While CO is a crucial component, it **does not fully determine MAP** without considering resistance - MAP can change significantly with alterations in peripheral resistance even when CO remains constant *Peripheral resistance alone* - While peripheral resistance is a key determinant, it **cannot establish MAP** without cardiac output - The volume of blood pumped (CO) must be present for resistance to generate pressure *Arterial compliance* - Arterial compliance primarily affects **pulse pressure** (systolic - diastolic), not mean arterial pressure - Reduced compliance (arterial stiffness) increases pulse pressure but has minimal direct effect on MAP - Compliance is more related to the pulsatile component rather than mean pressure

Question 912: What is the primary cause of the plateau phase in the cardiac muscle action potential?

A. The movement of fewer sodium ions across the cell membrane
B. The calcium channels remaining open longer than the sodium channels (Correct Answer)
C. The increased membrane permeability to potassium ion
D. A decrease in the amount of calcium diffusing across the membrane

Explanation: ***The calcium channels remaining open longer than the sodium channels*** - The **plateau phase** (Phase 2) of the cardiac action potential is primarily due to the sustained influx of **calcium ions** through long-lasting L-type calcium channels. - This **calcium influx** balances the efflux of potassium ions, maintaining depolarization for an extended period, which is crucial for effective cardiac contraction and preventing tetany. *The movement of fewer sodium ions across the cell membrane* - The rapid influx of **sodium ions** is responsible for the rapid depolarization (Phase 0) of the cardiac action potential, not the plateau phase. - **Sodium channels** inactivate quickly, contributing to repolarization rather than sustained depolarization. *The increased membrane permeability to potassium ion* - Increased permeability to **potassium ions** (efflux) is mainly responsible for repolarization (Phase 3) of the cardiac action potential, bringing the membrane potential back to its resting state. - During the plateau phase, potassium efflux is partially balanced by calcium influx. *A decrease in the amount of calcium diffusing across the membrane* - A decrease in **calcium diffusion** would lead to a shorter plateau phase or more rapid repolarization, not an sustained plateau. - The **sustained influx of calcium** is the defining characteristic of the plateau.

Question 913: Action potential conduction occurs at the fastest velocity in which part of the heart?

A. SA node
B. AV node
C. Purkinje fibers (Correct Answer)
D. Bundle of His

Explanation: ***Purkinje fibers*** - **Purkinje fibers** have a very large diameter and a high density of gap junctions, leading to the **fastest conduction velocity** (up to 4 m/s) in the heart. - This rapid conduction is crucial for the synchronized contraction of the **ventricular myocardium**. *SA node* - The **SA node** is the **primary pacemaker** and has the fastest intrinsic firing rate, but its conduction velocity within the nodal tissue is relatively slow. - It initiates the action potential, but its role is in rate generation, not rapid propagation throughout the ventricles. *AV node* - The **AV node** intentionally **slows down conduction** (0.05 m/s); this delay is critical to allow time for the atria to fully contract and fill the ventricles before ventricular contraction begins. - This delay prevents immediate propagation of atrial impulses to the ventricles. *Bundle of His* - The **Bundle of His** conducts impulses from the AV node to the bundle branches at a moderate velocity (1-2 m/s). - Its conduction speed is faster than that of the AV node but significantly slower than that of the Purkinje fibers.

Question 914: Which of the following is NOT a positive wave in the jugular venous pressure (JVP) tracing?

A. a wave (right atrial contraction)
B. c wave (tricuspid valve bulging)
C. x descent (atrial relaxation) (Correct Answer)
D. v wave (venous return increase during systole)

Explanation: ***x descent (atrial relaxation)*** - The **x descent** represents the **atrial relaxation** and the downward movement of the tricuspid annulus during ventricular systole, causing a drop in right atrial pressure, making it a **negative deflection**. - In JVP terminology, **waves** are positive deflections (a, c, v), while **descents** are negative deflections (x, y). - All other options describe positive waves in the JVP tracing. *a wave (right atrial contraction)* - The **a wave** is a **positive deflection** occurring late in diastole and represents the increase in right atrial pressure due to **atrial contraction**. - It precedes the first heart sound (S1) and is typically the most prominent positive wave. *c wave (tricuspid valve bulging)* - The **c wave** is a **positive deflection** occurring early in systole and is caused by the **bulging of the tricuspid valve** into the right atrium during isovolumic contraction of the right ventricle. - It coincides with the carotid pulse. *v wave (venous return increase during systole)* - The **v wave** is a **positive deflection** occurring in late systole and reflects the **passive filling of the right atrium** while the tricuspid valve is closed, causing an increase in pressure due to venous return. - It occurs after the second heart sound (S2) and immediately precedes the opening of the tricuspid valve.

Question 915: All are cardiovascular system changes in pregnancy except.

A. Increase in blood volume
B. Increase in heart rate
C. Increase in peripheral resistance (Correct Answer)
D. Increase in cardiac output

Explanation: ***Increase in peripheral resistance*** - During normal pregnancy, **peripheral vascular resistance actually decreases** due to the effects of hormones like progesterone and the presence of the low-resistance uteroplacental circulation. - This decrease in resistance helps accommodate the increased blood volume and cardiac output. *Increase in cardiac output* - **Cardiac output increases significantly** during pregnancy (by 30-50%) to meet the metabolic demands of the growing fetus and maternal tissues. - This is primarily achieved through an increase in both stroke volume and heart rate. *Increase in blood volume* - **Blood volume increases substantially** (by 30-50%) during pregnancy, with plasma volume increasing more than red blood cell mass. - This expansion supports the increased cardiac output and placental perfusion. *Increase in heart rate* - **Heart rate increases** during pregnancy, typically by 10-20 beats per minute, contributing to the overall increase in cardiac output. - This physiological adaptation helps maintain adequate circulation.

Question 916: The vasodilator involved in autoregulation of the coronary blood flow is:

A. Adenosine (Correct Answer)
B. CO2
C. Acetylcholine (ACh)
D. Nitric Oxide (NO)

Explanation: ***Adenosine*** - **Adenosine** is a potent local vasodilator produced by cardiac myocytes in response to increased metabolic activity or oxygen demand. - It acts to match **coronary blood flow** to myocardial oxygen consumption, particularly in conditions of increased cardiac work or reduced oxygen supply. *Acetylcholine (ACh)* - **Acetylcholine** primarily mediates vasodilation through endothelial-dependent mechanisms, stimulating **nitric oxide (NO)** release; however, it is not the primary mediator of metabolic autoregulation in the coronary circulation. - While it can cause vasodilation, it's more involved in **parasympathetic regulation** rather than local metabolic control of coronary flow. *CO2* - **Carbon dioxide (CO2)** is a potent vasodilator in the **cerebral circulation** and to some extent in other vascular beds, but its primary role in coronary autoregulation is less dominant compared to adenosine. - Increased CO2 levels typically reflect overall metabolic activity, but **adenosine** is a more direct and specific regulator for coronary blood flow in response to myocardial oxygen demand. *Nitric Oxide (NO)* - **Nitric oxide (NO)** is a crucial vasodilator in the coronary circulation, produced by endothelial cells, and plays a role in endothelium-dependent vasodilation. - While important for maintaining basal tone and mediating the effects of other vasodilators like acetylcholine, NO is not considered the primary local metabolic autoregulatory substance in response to myocardial oxygen demand; that role largely falls to **adenosine**.

Question 917: A 75-year-old woman is admitted to the hospital with anginal pain. The ECG reveals myocardial infarction and a right bundle branch block. During physical examination, the patient has a loud second heart sound. Which of the following heart valves are responsible for the production of the second heart sound?

A. Aortic and pulmonary (Correct Answer)
B. Aortic and tricuspid
C. Tricuspid and mitral
D. Mitral and pulmonary

Explanation: ***Aortic and pulmonary*** - The **second heart sound (S2)** is produced by the simultaneous closure of the **aortic valve** and the **pulmonary valve**. - A **loud S2** can indicate conditions like **systemic hypertension** (if the aortic component is loud) or **pulmonary hypertension** (if the pulmonary component is loud). *Aortic and tricuspid* - The **tricuspid valve** closure contributes to the **first heart sound (S1)**, not the second. - The second heart sound involves semilunar valves, not atrioventricular valves. *Tricuspid and mitral* - The closure of the **tricuspid** and **mitral valves** (atrioventricular valves) is responsible for the **first heart sound (S1)**. - S1 marks the beginning of ventricular systole. *Mitral and pulmonary* - The **mitral valve** closure contributes to the **first heart sound (S1)**. - The second heart sound is specifically from the closure of both semilunar valves.

Question 918: TGF-β is involved in all of the following processes of angiogenesis, except:

A. Increases the synthesis of collagen
B. Formation of the vascular lumen (Correct Answer)
C. Decreases the degradation of ECM
D. Stimulates fibroblast migration and proliferation

Explanation: ***Formation of the vascular lumen*** - TGF-β is **not directly involved** in forming the vascular lumen, which is primarily the result of endothelial cell behavior. - Its primary role in angiogenesis involves promoting other processes rather than lumen formation itself [1]. *Increases the synthesis of collagen* - TGF-β plays a significant role in **enhancing collagen synthesis**, contributing to tissue remodeling during angiogenesis [1]. - This process is critical for stabilizing blood vessels and is consistent with its role in **fibrosis**. *Stimulates fibroblast migration and proliferation* - TGF-β is known to **stimulate fibroblast migration** and proliferation, which aids in the formation of granulation tissue and new blood vessels [2]. - It is essential for wound healing and tissue repair processes involving angiogenesis. *Decreases the degradation of ECM* - TGF-β helps to **reduce ECM degradation**, promoting stability of newly formed blood vessels during angiogenesis [1]. - It regulates proteins that inhibit matrix metalloproteinases, thus retaining ECM integrity. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 115-116. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 117-119.

Question 919: The organ with maximum blood flow in milliliters per kilogram per minute during resting is:

A. Kidneys (Correct Answer)
B. Brain
C. Lungs
D. Liver

Explanation: ***Kidneys*** - The kidneys receive a disproportionately large share of cardiac output, approximately **20-25%**, which is essential for their role in **filtering blood** and maintaining fluid and electrolyte balance. - When adjusted for organ weight, the kidneys have the highest blood flow per unit mass due to their high metabolic demands for active transport and regulatory functions. *Liver* - The liver receives significant blood flow, but a substantial portion is **venous blood** from the portal system, which is lower in oxygen and nutrient content. - While total blood flow to the liver is high, its actual arterial supply and overall perfusion density per kilogram is lower than that of the kidneys. *Brain* - The brain has high metabolic demands and receives a constant and significant blood supply, typically around **15% of cardiac output**, to ensure adequate oxygen and glucose delivery. - However, when normalized per unit of tissue mass, its blood flow is less than that of the kidneys, which have specialized functions requiring extremely high perfusion. *Lungs* - The lungs receive the entire cardiac output through the **pulmonary circulation** for gas exchange, but this refers to the total volume of blood passing through, not the nutritive arterial supply to the lung tissue itself. - The bronchial circulation, which supplies oxygenated blood to the lung tissue, is relatively small compared to other highly metabolic organs.

Question 920: In the context of hypoxia, the cardiovascular response to peripheral chemoreceptor stimulation can result in which of the following changes in heart rate?

A. Only bradycardia
B. Either bradycardia or tachycardia (Correct Answer)
C. Neither bradycardia nor tachycardia
D. Only tachycardia

Explanation: ***Either bradycardia or tachycardia*** - Peripheral chemoreceptor stimulation by hypoxia produces **complex cardiovascular responses** that can result in either bradycardia or tachycardia depending on the circumstances. - **Direct chemoreceptor reflex**: Stimulation of carotid and aortic bodies causes **reflex bradycardia** via vagal activation (direct effect). - **Net clinical effect**: In most physiological conditions, the bradycardia is overridden by **compensatory tachycardia** due to: - Sympathetic nervous system activation - Hyperventilation-induced stretch receptor stimulation - Direct myocardial effects attempting to maintain oxygen delivery - The actual heart rate response depends on the **balance between vagal and sympathetic inputs**, making both responses possible. *Only bradycardia* - While isolated peripheral chemoreceptor stimulation can produce **reflex bradycardia**, this ignores the compensatory sympathetic activation that typically occurs during hypoxia. - In clinical hypoxia, bradycardia alone is uncommon unless other factors suppress sympathetic responses. *Neither bradycardia nor tachycardia* - This is incorrect because peripheral chemoreceptor stimulation **invariably affects heart rate** through autonomic pathways. - The cardiovascular system must respond to hypoxia to maintain oxygen delivery to tissues. *Only tachycardia* - While **tachycardia** is the more common net clinical response to hypoxia, the initial chemoreceptor reflex involves **vagal bradycardia**. - Stating "only tachycardia" ignores the direct chemoreceptor-vagal reflex pathway and the possibility of bradycardia in certain experimental or clinical conditions.

Practice by Chapter

Cardiac Electrophysiology

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Cardiac Cycle

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Cardiac Output and Its Regulation

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Hemodynamics and Blood Flow

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Arterial System Physiology

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Microcirculation and Lymphatics

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Venous Return and Central Venous Pressure

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Cardiovascular Reflexes

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Regional Circulations

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Cardiovascular Responses to Exercise and Stress

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