Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 231: Which fibers in the ventricle depolarize most rapidly?

A. Fibers at the apex
B. Fibers in the middle of the ventricle
C. Fibers at the base (Correct Answer)
D. All fibers from apex to base depolarize equally rapidly

Explanation: **Explanation:** The sequence of ventricular depolarization is a high-yield concept in cardiac physiology. While the Purkinje system ensures a rapid and coordinated contraction, the depolarization process follows a specific spatial vector: it begins at the **interventricular septum**, moves toward the **apex**, and finally reaches the **base of the ventricle**. **Why the Base Depolarizes Most Rapidly:** The "rapidity" in this context refers to the terminal phase of ventricular activation. The basal portions of the ventricles (near the atrioventricular groove) and the posterobasal portion of the left ventricle are the **last areas to depolarize**. Because the Purkinje network is most dense in the subendocardium and tapers toward the base, the impulse travels through the thick ventricular walls to reach the base last. Consequently, the electrical vector directed toward the base represents the final, most rapid surge of depolarization before the entire ventricle becomes isoelectric (ST segment). **Analysis of Incorrect Options:** * **Option A (Apex):** Depolarization reaches the apex shortly after the septum. While the apex contracts early to push blood upward, it is not the site of the final, most rapid depolarization phase. * **Option B (Middle):** The mid-ventricular walls depolarize after the apex but before the base. * **Option D (Equal):** Depolarization is not simultaneous; there is a measurable physiological delay (approx. 0.06 seconds) from the start of the QRS complex to the activation of the basal fibers. **NEET-PG High-Yield Pearls:** * **Direction of Depolarization:** Endocardium to Epicardium. * **Direction of Repolarization:** Epicardium to Endocardium (this is why the T-wave is normally upright, same as the QRS). * **Last part to depolarize:** Posterobasal part of the Left Ventricle and the Pulmonary Conus. * **Purkinje Fiber Velocity:** 1.5 to 4.0 m/s (Fastest conduction in the heart).

Question 232: Which organ receives the maximum blood flow in ml/kg/min?

A. Kidney (Correct Answer)
B. Heart
C. Brain
D. Adrenal gland

Explanation: **Explanation:** The distribution of cardiac output can be measured in two ways: total blood flow (ml/min) or **specific organ blood flow (ml/100g/min or ml/kg/min)**. **1. Why Kidney is Correct:** The kidneys receive approximately 20-25% of the total cardiac output (about 1100-1200 ml/min). When adjusted for weight, the kidney receives roughly **360-400 ml/100g/min**. This high flow is not primarily for metabolic demand, but to maintain a high Glomerular Filtration Rate (GFR) for effective waste excretion and electrolyte balance. **2. Analysis of Incorrect Options:** * **Heart:** The coronary blood flow is approximately **70-80 ml/100g/min**. While the heart has the highest oxygen extraction ratio, its weight-adjusted blood flow is significantly lower than the kidney. * **Brain:** Cerebral blood flow is constant at approximately **50-54 ml/100g/min**. The brain prioritizes autoregulation over high-volume flow. * **Adrenal Gland:** While the adrenal glands have the highest blood flow *per gram of tissue* among endocrine organs (approx. 300 ml/100g/min), the **Kidney** still remains the standard answer for the highest specific blood flow in most physiological contexts and competitive exams. **High-Yield NEET-PG Pearls:** * **Highest Total Blood Flow (ml/min):** Liver (receives ~1500 ml/min via dual supply). * **Highest Specific Blood Flow (ml/100g/min):** Kidney (among major organs). *Note: Some texts cite the Carotid Body as having the absolute highest (2000 ml/100g/min), but it is rarely an option.* * **Highest A-V Oxygen Difference:** Heart (extracts maximum $O_2$ per unit of blood). * **Highest $O_2$ Consumption per 100g:** Heart.

Question 233: Preload leads to which of the following?

A. Isovolumetric relaxation
B. Isovolumetric contraction (Correct Answer)
C. Peripheral resistance
D. Parasympathetic nervous system activation

Explanation: **Explanation:** **Preload** refers to the initial stretching of the cardiac myocytes prior to contraction. In clinical terms, it is the **End-Diastolic Volume (EDV)**—the amount of blood in the ventricles at the end of filling. **Why Isovolumetric Contraction is correct:** According to the **Frank-Starling Law**, an increase in preload (EDV) increases the stretch of the ventricular fibers, leading to a more forceful contraction. The phase of the cardiac cycle that immediately follows the end of diastole (where preload is established) is **Isovolumetric Contraction**. During this phase, the ventricles begin to contract with all valves closed, building pressure to overcome afterload. Therefore, preload directly determines the tension generated during this specific phase. **Analysis of Incorrect Options:** * **A. Isovolumetric Relaxation:** This occurs at the beginning of diastole, after the aortic/pulmonary valves close. It is influenced by the rate of calcium reuptake (lusitropy), not the initial stretch (preload). * **C. Peripheral Resistance:** This is a component of **Afterload**, representing the resistance the heart must pump against, primarily determined by arteriolar tone. * **D. Parasympathetic Activation:** This decreases heart rate (chronotropy) but has minimal effect on preload-driven contraction force in the ventricles. **High-Yield Clinical Pearls for NEET-PG:** * **Frank-Starling Law:** Stroke Volume $\propto$ Preload. It ensures that the output of both ventricles remains balanced. * **Preload Markers:** Left Ventricular End-Diastolic Pressure (LVEDP) or Pulmonary Capillary Wedge Pressure (PCWP). * **Factors increasing Preload:** Hypervolemia, regurgitant valves, and increased venous return (e.g., leg elevation). * **Factors decreasing Preload:** Diuretics, venodilators (Nitroglycerin), and hemorrhage.

Question 234: If the ejection fraction increases, what will decrease?

A. Cardiac output
B. End-systolic volume (Correct Answer)
C. Heart rate
D. Pulse pressure

Explanation: ### Explanation **Concept Overview** Ejection Fraction (EF) is the percentage of blood pumped out of the left ventricle with each contraction. It is mathematically defined as: **EF = (Stroke Volume / End-Diastolic Volume) × 100** Since Stroke Volume (SV) is the difference between the blood in the ventricle before contraction (EDV) and after contraction (ESV), the formula can be rewritten as: **EF = (EDV – ESV) / EDV** **Why End-Systolic Volume (ESV) Decreases** An increase in EF implies that the heart is pumping more efficiently, ejecting a larger proportion of the EDV. If the heart squeezes more effectively (increased contractility), less blood remains in the ventricle at the end of the contraction. Therefore, **ESV must decrease** as more blood is shifted into the Stroke Volume. **Analysis of Incorrect Options** * **A. Cardiac Output:** Since Cardiac Output = Stroke Volume × Heart Rate, an increase in EF (which increases SV) typically leads to an **increase** in cardiac output, not a decrease. * **C. Heart Rate:** There is no direct physiological rule that heart rate must decrease when EF increases, although in a compensated state (like an athlete's heart), a high SV may allow for a lower resting HR. However, it is not a mathematical certainty like ESV. * **D. Pulse Pressure:** Pulse pressure is directly proportional to Stroke Volume. Since an increased EF increases SV, the pulse pressure would generally **increase**. **High-Yield Clinical Pearls for NEET-PG** * **Normal EF:** Typically 55–70%. An EF <40% is diagnostic of Heart Failure with reduced Ejection Fraction (HFrEF). * **Best Indicator of Contractility:** While EF is commonly used, the **End-Systolic Pressure-Volume Relationship (ESPVR)** is the most accurate clinical measure of contractility. * **Effect of Inotropes:** Positive inotropes (like Digoxin or Dobutamine) increase EF by decreasing ESV.

Question 235: Which of the following best describes the primary function of arterioles?

A. Regulation of vascular resistance (Correct Answer)
B. Gas and nutrient exchange
C. Blood reservoir
D. Maintenance of blood pressure

Explanation: ### Explanation **Correct Option: A. Regulation of vascular resistance** Arterioles are known as the **"Resistance Vessels"** of the circulatory system. They possess a thick layer of circular smooth muscle in their walls, which is richly innervated by sympathetic adrenergic fibers. By undergoing vasoconstriction or vasodilation, arterioles provide the greatest resistance to blood flow (approximately 50-70% of total peripheral resistance). This regulation is crucial for controlling the blood flow to specific organs and protecting the delicate capillary beds from high arterial pressures. **Analysis of Incorrect Options:** * **B. Gas and nutrient exchange:** This is the primary function of **Capillaries**. Capillaries have thin walls (single layer of endothelium) and slow blood flow velocity, which facilitates the diffusion of gases and nutrients. * **C. Blood reservoir:** This describes **Veins and Venules**, often called **"Capacitance Vessels."** Due to their high compliance, they hold approximately 60-70% of the total blood volume at any given time. * **D. Maintenance of blood pressure:** While arterioles contribute to blood pressure via peripheral resistance, the **Large Elastic Arteries** (like the Aorta) are primarily responsible for maintaining diastolic blood pressure through their elastic recoil (Windkessel effect). **High-Yield Clinical Pearls for NEET-PG:** * **Poiseuille’s Law:** Resistance is inversely proportional to the fourth power of the radius ($R \propto 1/r^4$). Thus, even a small change in arteriolar diameter significantly impacts blood flow. * **Pre-capillary Sphincters:** Located at the arteriolar-capillary junction, these regulate the number of active capillaries in a tissue bed. * **Site of Maximum Pressure Drop:** The largest drop in mean arterial pressure occurs across the arterioles (from ~85 mmHg to ~35 mmHg).

Question 236: What is true about shock?

A. In the early stage, cardiac output and BP are maintained.
B. There is decreased sympathetic activity.
C. Renin secretion may be increased. (Correct Answer)
D. Aldosterone secretion is decreased.

Explanation: **Explanation:** Shock is a state of acute circulatory failure resulting in inadequate tissue perfusion. The body’s primary response to shock involves compensatory mechanisms aimed at maintaining blood pressure and vital organ perfusion. **Why Option C is Correct:** In shock (especially hypovolemic and cardiogenic), decreased renal perfusion pressure is sensed by the juxtaglomerular apparatus. This triggers the **Renin-Angiotensin-Aldosterone System (RAAS)**. Increased **Renin** secretion leads to the production of Angiotensin II (a potent vasoconstrictor) and **Aldosterone**, which promotes sodium and water retention to restore intravascular volume. **Analysis of Incorrect Options:** * **Option A:** In the early (compensated) stage of shock, compensatory mechanisms (like tachycardia and peripheral vasoconstriction) may maintain **Blood Pressure**, but **Cardiac Output (CO)** is typically already reduced. A normal BP does not rule out shock. * **Option B:** Shock triggers a massive **increase in sympathetic activity** via the baroreceptor reflex. This leads to tachycardia, increased myocardial contractility, and peripheral vasoconstriction (except in distributive shock). * **Option D:** As part of the RAAS activation mentioned above, **Aldosterone secretion is increased**, not decreased, to conserve fluid. **High-Yield Clinical Pearls for NEET-PG:** * **Warm vs. Cold Shock:** Most shocks present with cold, clammy skin due to sympathetic vasoconstriction. However, **Early Septic Shock** (Distributive) presents with "warm shock" due to peripheral vasodilation and increased CO. * **The Golden Hour:** Refers to the critical period where aggressive fluid resuscitation and addressing the underlying cause can reverse the compensatory stage before it progresses to irreversible organ damage. * **Refractory Shock:** A stage where the patient no longer responds to vasopressors or volume replacement, often due to severe metabolic acidosis and "vasomotor paralysis."

Question 237: What produces the first heart sound?

A. Closure of the aortic and pulmonary valves
B. Opening of the aortic and pulmonary valves
C. Closure of the mitral and tricuspid valves (Correct Answer)
D. Opening of the mitral and tricuspid valves

Explanation: ### Explanation The **First Heart Sound (S1)** is produced by the sudden closure of the **Atrioventricular (AV) valves**—the **Mitral** and **Tricuspid** valves. This occurs at the beginning of **ventricular systole** when the intraventricular pressure rises above the atrial pressure, forcing the valves shut to prevent backflow. The sound itself is generated by the vibration of the valves and the surrounding blood and ventricular walls. #### Analysis of Options: * **Option C (Correct):** Closure of the mitral and tricuspid valves marks the onset of systole. The mitral component (M1) usually precedes the tricuspid component (T1). * **Option A (Incorrect):** Closure of the semilunar valves (Aortic and Pulmonary) produces the **Second Heart Sound (S2)**, marking the end of systole and the beginning of diastole. * **Options B & D (Incorrect):** Under normal physiological conditions, the **opening** of heart valves is silent. If valve opening produces a sound, it is pathological (e.g., an Opening Snap in Mitral Stenosis or an Ejection Click in Aortic Stenosis). #### High-Yield NEET-PG Pearls: * **Timing:** S1 coincides with the **isovolumetric contraction phase** of the cardiac cycle and the peak of the **R-wave** on an ECG. * **Character:** S1 is lower in pitch and longer in duration ("Lubb") compared to S2 ("Dupp"). * **Best heard at:** The Mitral area (5th intercostal space, mid-clavicular line). * **Loud S1:** Seen in Mitral Stenosis (due to stiff leaflets) and Tachycardia. * **Soft S1:** Seen in Mitral Regurgitation and Heart Failure.

Question 238: Cardiac output is increased in which of the following conditions?

A. Sleep
B. Pregnancy (Correct Answer)
C. Sitting
D. Standing

Explanation: **Explanation:** **Correct Answer: B. Pregnancy** **Mechanism:** Cardiac Output (CO) is the product of Stroke Volume (SV) and Heart Rate (HR). In **pregnancy**, CO increases significantly (by 30–50%). This is driven by a physiological increase in blood volume (to meet fetal demands) and a decrease in systemic vascular resistance (due to the vasodilatory effects of progesterone and the low-resistance placental circulation). Both SV and HR increase, peaking around the 20th–24th week of gestation. **Analysis of Incorrect Options:** * **A. Sleep:** During sleep, the body’s metabolic demand decreases. Parasympathetic activity dominates, leading to a decrease in heart rate and blood pressure, which results in a **decreased** CO. * **C & D. Sitting and Standing:** When moving from a supine to an upright position (sitting or standing), gravity causes blood to pool in the lower extremities (venous pooling). This reduces venous return (preload), leading to a decrease in stroke volume and a subsequent **decrease** in CO (by approximately 20%). **High-Yield NEET-PG Pearls:** * **Factors Increasing CO:** Exercise (highest increase), Pregnancy, Anxiety/Excitement, Eating (post-prandial), High altitude, and Anemia (due to decreased viscosity). * **Factors Decreasing CO:** Change from recumbent to upright position, Rapid arrhythmias (due to decreased filling time), and Heart failure. * **Formula:** $CO = SV \times HR$. In early pregnancy, the increase is mainly due to SV; in late pregnancy, HR contributes more. * **Positioning Tip:** In late pregnancy, CO can actually decrease when supine due to **Aortocaval compression** (the gravid uterus compressing the Inferior Vena Cava). This is why the left lateral position is preferred.

Question 239: A standing person lies down. Which of the following physiological changes occurs immediately?

A. Increased heart rate
B. Decreased blood flow to the apices of the lung
C. Immediate increase in venous return (Correct Answer)
D. Increase in blood pressure

Explanation: **Explanation:** The transition from a standing to a lying position (supine) eliminates the effect of gravity on the column of blood in the lower extremities. **1. Why "Immediate increase in venous return" is correct:** When standing, approximately 500–1000 mL of blood pools in the lower limbs due to gravity (venous pooling). Upon lying down, this pooled blood is displaced centrally toward the heart. This results in an **immediate increase in venous return** to the right atrium, which subsequently increases the **End-Diastolic Volume (EDV)** and stroke volume via the Frank-Starling mechanism. **2. Why the other options are incorrect:** * **Increased heart rate:** The increase in venous return leads to an increase in stroke volume and mean arterial pressure. This stimulates the **baroreceptor reflex**, which leads to a compensatory **decrease** in heart rate (bradycardia) to maintain cardiac output. * **Decreased blood flow to the apices:** In a standing position, apical blood flow is low due to gravity (Zone 1/2 of West). In the supine position, gravity acts equally across the lung from ventral to dorsal surfaces, leading to a **more uniform distribution** and an **increase** in blood flow to the apices. * **Increase in blood pressure:** While there is a transient rise in pressure due to increased stroke volume, the body immediately activates the baroreflex to normalize it. Therefore, a sustained "increase" is not the primary physiological goal; the most immediate hemodynamic event is the shift in venous volume. **High-Yield Clinical Pearls for NEET-PG:** * **Bainbridge Reflex:** An increase in venous return stretches atrial receptors, which can cause a transient increase in HR to "pump out" the excess volume. However, the **Baroreceptor reflex** usually dominates in humans during postural changes, leading to a net decrease in HR. * **Orthostatic Hypotension:** Defined as a drop in systolic BP >20 mmHg or diastolic BP >10 mmHg within 3 minutes of standing. * **ANP Release:** The stretch of the right atrium due to increased venous return in the supine position leads to the release of **Atrial Natriuretic Peptide (ANP)**, promoting diuresis.

Question 240: Flow is laminar in small vessels because:

A. Reynolds number is >2000
B. Total cross-sectional area of small vessels is smaller
C. Diameter of smaller vessels is less
D. Effective velocity in small vessels is less (Correct Answer)

Explanation: ### Explanation The type of blood flow (laminar vs. turbulent) is determined by the **Reynolds number (Re)**. The formula for Reynolds number is: $$Re = \frac{\rho \cdot D \cdot v}{\eta}$$ *(Where $\rho$ = density, $D$ = diameter, $v$ = velocity, and $\eta$ = viscosity)* Laminar flow occurs when $Re$ is low (typically <2000). In the microcirculation (small vessels like arterioles and capillaries), the **effective velocity ($v$)** of blood flow is extremely low. Even though individual small vessels have tiny diameters, their **total cross-sectional area** is massive compared to the aorta. According to the Law of Continuity ($Q = A \times v$), as the total cross-sectional area ($A$) increases, the velocity ($v$) must decrease. This profound drop in velocity is the primary factor that keeps the Reynolds number very low, ensuring stable laminar flow. **Analysis of Options:** * **Option A (Incorrect):** A Reynolds number >2000 indicates a transition toward **turbulent flow**, not laminar. * **Option B (Incorrect):** The total cross-sectional area of small vessels (capillaries) is actually **much larger** (approx. 1000 times) than that of the aorta. * **Option C (Incorrect):** While diameter ($D$) is smaller, the Reynolds formula shows that $D$ and $v$ are both in the numerator. However, the decrease in velocity ($v$) in small vessels is much more significant in maintaining laminar flow than the diameter alone. * **Option D (Correct):** The significantly reduced velocity in the vast capillary bed ensures $Re$ remains low, favoring laminar flow. **High-Yield NEET-PG Pearls:** 1. **Velocity vs. Area:** Velocity of blood flow is **inversely proportional** to the total cross-sectional area. Velocity is highest in the aorta and lowest in the capillaries. 2. **Turbulence:** Most likely to occur in the **Aorta** (high diameter and velocity) or in conditions like **Anemia** (decreased viscosity $\eta$). 3. **Bruit/Murmur:** These are clinical manifestations of turbulent flow.

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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