Cardiovascular System Practice Questions

Q: Which fibers in the ventricle depolarize most rapidly?

Fibers at the base. **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).

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

Kidney. **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.

Q: Preload leads to which of the following?

Isovolumetric contraction. **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.

Q: If the ejection fraction increases, what will decrease?

End-systolic volume. ### 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.

Q: Which of the following best describes the primary function of arterioles?

Regulation of vascular resistance. ### 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).

Q: What produces the first heart sound?

Closure of the mitral and tricuspid valves. ### 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.

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

Pregnancy. **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 1

Which fibers in the ventricle depolarize most rapidly?

Accepted Answer

Fibers at the base

Answer

Fibers at the apex

Answer

Fibers in the middle of the ventricle

Answer

All fibers from apex to base depolarize equally rapidly

Question 2

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

Accepted Answer

Kidney

Answer

Heart

Answer

Brain

Answer

Adrenal gland

Question 3

Preload leads to which of the following?

Accepted Answer

Isovolumetric contraction

Answer

Isovolumetric relaxation

Answer

Peripheral resistance

Answer

Parasympathetic nervous system activation

Question 4

If the ejection fraction increases, what will decrease?

Accepted Answer

End-systolic volume

Answer

Cardiac output

Answer

Heart rate

Answer

Pulse pressure

Question 5

Which of the following best describes the primary function of arterioles?

Accepted Answer

Regulation of vascular resistance

Answer

Gas and nutrient exchange

Answer

Blood reservoir

Answer

Maintenance of blood pressure

Question 6

What is true about shock?

Accepted Answer

Renin secretion may be increased.

Answer

In the early stage, cardiac output and BP are maintained.

Answer

There is decreased sympathetic activity.

Answer

Aldosterone secretion is decreased.

Question 7

What produces the first heart sound?

Accepted Answer

Closure of the mitral and tricuspid valves

Answer

Closure of the aortic and pulmonary valves

Answer

Opening of the aortic and pulmonary valves

Answer

Opening of the mitral and tricuspid valves

Question 8

Cardiac output is increased in which of the following conditions?

Accepted Answer

Pregnancy

Answer

Sleep

Answer

Sitting

Answer

Standing

Question 9

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

Accepted Answer

Immediate increase in venous return

Answer

Increased heart rate

Answer

Decreased blood flow to the apices of the lung

Answer

Increase in blood pressure

Question 10

Flow is laminar in small vessels because:

Accepted Answer

Effective velocity in small vessels is less

Answer

Reynolds number is >2000

Answer

Total cross-sectional area of small vessels is smaller

Answer

Diameter of smaller vessels is less

Cardiovascular System — MCQs

Cardiovascular System — MCQs

On this page

Practice by Chapter

Want unlimited practice?