Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 331: What is the primary system responsible for transporting blood throughout the human body?

A. Urinary system
B. Circulatory system (Correct Answer)
C. Lymphatic system
D. Digestive system

Explanation: The **Circulatory System** (also known as the cardiovascular system) is the primary transport network of the body. It consists of the heart (the pump), blood vessels (the conduits), and blood (the medium). Its fundamental role is to deliver oxygen and nutrients to tissues while removing metabolic waste products like carbon dioxide. This is achieved through two major circuits: the pulmonary circulation (for gas exchange) and the systemic circulation (for tissue perfusion). **Analysis of Incorrect Options:** * **Urinary System:** Its primary role is the filtration of blood to maintain electrolyte balance, acid-base homeostasis, and the excretion of nitrogenous wastes (urea/creatinine) via urine. * **Lymphatic System:** While it transports "lymph" (excess interstitial fluid), its primary functions are immune surveillance and the absorption of dietary lipids (chylomicrogens) from the small intestine. It is an accessory to the circulatory system but not the primary transport for blood. * **Digestive System:** This system is responsible for the mechanical and chemical breakdown of food and the absorption of nutrients into the bloodstream; it does not transport blood itself. **Clinical Pearls for NEET-PG:** * **Starling’s Law:** The heart's stroke volume increases in response to an increase in the volume of blood filling the heart (end-diastolic volume). * **Total Peripheral Resistance (TPR):** Arterioles are the primary "resistance vessels" that regulate blood pressure. * **Velocity of Flow:** Blood flow velocity is lowest in the **capillaries** due to their large total cross-sectional area, allowing maximum time for nutrient exchange.

Question 332: Endothelium-derived relaxing factor is:

A. Nitric oxide (Correct Answer)
B. Angiotensin
C. Serotonin
D. Norepinephrine

Explanation: **Explanation:** **Endothelium-derived relaxing factor (EDRF)** is a potent endogenous vasodilator produced by vascular endothelial cells. In 1987, researchers (Furchgott and Ignarro) identified that EDRF is actually **Nitric Oxide (NO)**. 1. **Why Nitric Oxide is Correct:** NO is synthesized from the amino acid **L-arginine** by the enzyme **Nitric Oxide Synthase (NOS)**. Once released, it diffuses into the underlying vascular smooth muscle cells and activates the enzyme **soluble Guanylyl Cyclase (sGC)**. This increases levels of **cyclic GMP (cGMP)**, which leads to dephosphorylation of myosin light chains, resulting in smooth muscle relaxation and vasodilation. 2. **Why Other Options are Incorrect:** * **Angiotensin (II):** A potent **vasoconstrictor** and a key component of the Renin-Angiotensin-Aldosterone System (RAAS). * **Serotonin (5-HT):** Generally acts as a **vasoconstrictor** in damaged blood vessels to assist in hemostasis, though its effects can vary by receptor subtype. * **Norepinephrine:** Acts on $\alpha_1$-adrenergic receptors to cause systemic **vasoconstriction**. **High-Yield Clinical Pearls for NEET-PG:** * **Stimuli for NO release:** Shear stress (blood flow), Acetylcholine, Bradykinin, and Histamine. * **Mechanism:** NO $\rightarrow$ $\uparrow$ cGMP $\rightarrow$ Vasodilation (Remember: Sildenafil/Viagra inhibits PDE-5, preventing cGMP breakdown). * **Nitroglycerin:** Acts by being converted into Nitric Oxide, providing rapid relief in Angina Pectoris. * **Septic Shock:** Overproduction of NO by inducible NOS (iNOS) leads to the characteristic massive vasodilation and hypotension.

Question 333: According to the Frank-Starling law, to what is the extent of preload proportional?

A. Increase in heart rate
B. End-diastolic volume (Correct Answer)
C. End-systolic volume
D. Ejection systolic volume

Explanation: ### Explanation **The Core Concept: Frank-Starling Law** The Frank-Starling Law of the heart states that the force of ventricular contraction is directly proportional to the initial length of the cardiac muscle fibers. In clinical physiology, the **End-Diastolic Volume (EDV)** serves as the primary measure of this "initial length" or **Preload**. As the ventricle fills with more blood during diastole, the myocardial fibers are stretched; this stretch optimizes the overlap between actin and myosin filaments, leading to an increased force of contraction and a higher stroke volume. **Analysis of Options:** * **B. End-diastolic volume (Correct):** This represents the volume of blood in the ventricles just before systole begins. It is the gold-standard physiological parameter for preload. * **A. Increase in heart rate:** While an increase in heart rate can increase cardiac output, it is not the basis of the Frank-Starling mechanism. In fact, excessive tachycardia can decrease preload by shortening diastolic filling time. * **C. End-systolic volume:** This is the volume remaining in the ventricle *after* contraction. It reflects afterload and contractility rather than the initial stretch (preload). * **D. Ejection systolic volume:** This is a distractor term; the volume ejected is the "Stroke Volume," which is the *result* of the Frank-Starling mechanism, not the measure of preload itself. **NEET-PG High-Yield Pearls:** * **Preload** is synonymous with **End-Diastolic Fiber Length** or **EDV**. * **Afterload** is the resistance the heart must pump against (represented by Mean Arterial Pressure). * The Frank-Starling curve shifts **upward and to the left** with positive inotropic agents (e.g., Digoxin, Adrenaline) and **downward** in heart failure. * The mechanism is "intrinsic" to the heart and does not require nerve input (it occurs in denervated, transplanted hearts).

Question 334: Which of the following occurs due to filtration at the arteriolar end of the capillary bed?

A. Decrease in hydrostatic pressure of capillaries
B. Increase in hydrostatic pressure of capillaries (Correct Answer)
C. Increase in oncotic pressure of capillaries
D. Decrease in oncotic pressure of interstitium

Explanation: ### Explanation The movement of fluid across capillary walls is governed by **Starling’s Forces**. At the arteriolar end of the capillary, the **Capillary Hydrostatic Pressure ($P_c$)** is the primary driving force that pushes fluid out into the interstitium (filtration). **Why the Correct Answer is Right:** As blood enters the capillary bed from the high-resistance arterioles, the **Capillary Hydrostatic Pressure ($P_c$)** is at its peak (approx. 30–35 mmHg). This pressure is significantly higher than the opposing Interstitial Hydrostatic Pressure and the Capillary Oncotic Pressure. Therefore, the "increase" or presence of high hydrostatic pressure is the physiological prerequisite and cause for filtration to occur at this end. **Analysis of Incorrect Options:** * **Option A:** A decrease in hydrostatic pressure would favor reabsorption, not filtration. Hydrostatic pressure actually drops as blood moves toward the venous end. * **Option C:** As fluid is filtered out, the concentration of non-diffusible plasma proteins (like albumin) remaining in the capillary increases. This leads to an **increase in Capillary Oncotic Pressure ($\pi_c$)** as a *result* of filtration, but it is not the *cause* of filtration. * **Option D:** Filtration moves fluid into the interstitium, which would typically dilute the interstitial proteins, potentially decreasing interstitial oncotic pressure. However, this is a secondary effect and not the mechanism driving the initial filtration. **High-Yield NEET-PG Pearls:** 1. **Starling Equation:** $Net\ Filtration = K_f [(P_c - P_i) - \sigma(\pi_c - \pi_i)]$. 2. **Albumin** is the chief determinant of Capillary Oncotic Pressure ($\pi_c$); hypoalbuminemia (e.g., Nephrotic syndrome, Cirrhosis) leads to edema due to decreased $\pi_c$. 3. **Arteriolar Dilatation** increases $P_c$ and promotes edema, while **Arteriolar Constriction** decreases $P_c$ and protects against edema. 4. The **Lymphatic system** is responsible for returning the small amount of net filtrate (not reabsorbed at the venous end) back into the circulation.

Question 335: Which scientific principle is the basis of the thermodilution method used in the measurement of cardiac output?

A. Hagen-Poiseuille principle
B. Bernoulli's principle
C. Stewart-Hamilton principle (Correct Answer)
D. Universal gas equation

Explanation: ### Explanation **Correct Answer: C. Stewart-Hamilton principle** The **Stewart-Hamilton principle** is the foundation of the indicator-dilution method, of which **thermodilution** is a specific type. In this method, a known quantity of an indicator (cold saline) is injected into the right atrium. A thermistor at the tip of a Swan-Ganz catheter (positioned in the pulmonary artery) measures the change in temperature over time. The cardiac output is inversely proportional to the area under the temperature-time curve. Simply put: the faster the blood flows, the quicker the indicator is diluted and cleared. **Analysis of Incorrect Options:** * **A. Hagen-Poiseuille principle:** Describes the relationship between flow, pressure, and resistance in a laminar fluid system ($Q = \Delta P/R$). It explains how vessel diameter significantly impacts blood flow resistance but does not measure cardiac output. * **B. Bernoulli's principle:** States that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure. In cardiology, it is used in echocardiography to calculate pressure gradients across stenotic valves. * **C. Universal gas equation ($PV=nRT$):** Relates pressure, volume, and temperature of an ideal gas; it has no direct application in measuring hemodynamic flow. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard:** While the **Fick Principle** (based on oxygen consumption) is the theoretical gold standard, **Thermodilution** is the most common clinical method used in ICUs. * **Site of Injection:** Cold saline is injected into the **Right Atrium**, and temperature change is sensed in the **Pulmonary Artery**. * **Inaccuracy:** Thermodilution can yield inaccurate results in patients with significant **tricuspid regurgitation** or intracardiac shunts.

Question 336: A fall in blood pressure occurs in which of the following situations?

A. Sympathetic stimulation
B. Inhibition of the vasomotor center (Correct Answer)
C. Disinhibition of the vasomotor center
D. Stimulation of the vagal center

Explanation: **Explanation:** Blood pressure (BP) is primarily regulated by the **Vasomotor Center (VMC)** located in the medulla oblongata. The VMC maintains a continuous state of partial contraction in blood vessels (vasomotor tone) via sympathetic outflow. **Why Option B is Correct:** The Vasomotor Center is the "pressor" area of the brain. **Inhibition of the VMC** leads to a decrease in sympathetic outflow to the heart and peripheral blood vessels. This results in peripheral vasodilation (decreased Total Peripheral Resistance) and a decrease in heart rate and myocardial contractility (decreased Cardiac Output). Since $BP = CO \times TPR$, a reduction in both parameters leads to a significant fall in blood pressure. **Analysis of Incorrect Options:** * **Option A (Sympathetic stimulation):** This increases BP by causing vasoconstriction (via $\alpha_1$ receptors) and increasing heart rate/contractility (via $\beta_1$ receptors). * **Option C (Disinhibition of VMC):** Disinhibition means removing an inhibitory influence (like the baroreceptor reflex). This results in overactivity of the VMC, leading to an increase in BP. * **Option D (Stimulation of the vagal center):** While vagal stimulation (parasympathetic) decreases heart rate, it has negligible effects on peripheral blood vessels. While it can lower BP, the **inhibition of the VMC** is a more potent and direct cause of a systemic fall in BP because it affects both the heart and the entire peripheral vascular resistance. **NEET-PG High-Yield Pearls:** * **Baroreceptor Reflex:** An increase in BP stimulates baroreceptors, which send signals via the Glossopharyngeal (CN IX) and Vagus (CN X) nerves to the **Nucleus Tractus Solitarius (NTS)**. The NTS then **inhibits the VMC**, leading to a fall in BP. * **VMC Components:** It consists of the C1 (vasoconstrictor) area and the A1 (vasodepressor) area. * **Cushing Reflex:** Increased intracranial pressure leads to VMC stimulation, causing a classic triad of Hypertension, Bradycardia, and Irregular Respiration.

Question 337: What is the Na+: Ca++ binding ratio on the sodium-calcium exchanger (NCX) in the myocardial fibers?

A. 1:01
B. 1:03
C. 3:01 (Correct Answer)
D. 4:01

Explanation: **Explanation:** The **Sodium-Calcium Exchanger (NCX)** is a secondary active transport mechanism located on the sarcolemma of myocardial fibers. It plays a critical role in cardiac relaxation (lusitropy) by removing calcium from the cytoplasm. **1. Why 3:1 is Correct:** The NCX operates by moving **3 Na⁺ ions** into the cell in exchange for **1 Ca²⁺ ion** moving out of the cell (during the relaxation phase). Because three positive charges (3x Na⁺) enter for every two positive charges (1x Ca²⁺) that leave, the process is **electrogenic**, creating a net inward current ($I_{NaCa}$). This stoichiometry is essential for maintaining the low intracellular calcium levels required for diastole. **2. Analysis of Incorrect Options:** * **1:1 (Option A):** This would be electrically neutral. If the ratio were 1:1, the exchanger would not have enough driving force from the sodium gradient to effectively move calcium against its steep concentration gradient. * **1:3 (Option B):** This is the reverse of the actual ratio. Moving 3 Ca²⁺ for 1 Na⁺ would be energetically impossible under physiological conditions. * **4:1 (Option D):** While some specialized exchangers in other tissues (like the NCKX in the retina) use a 4:1 ratio (often involving Potassium), the standard myocardial NCX specifically utilizes a 3:1 ratio. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Digitalis Mechanism:** Digoxin inhibits the Na⁺-K⁺ ATPase, increasing intracellular Na⁺. This reduces the Na⁺ gradient, slowing down the NCX. Consequently, less Ca²⁺ is pumped out, leading to increased intracellular Ca²⁺ and increased contractility (**Positive Inotropy**). * **Reverse Mode:** During Phase 2 (Plateau) of the cardiac action potential, the NCX can briefly run in "reverse mode," bringing Ca²⁺ into the cell. * **Calcium Removal:** In the myocardium, ~70% of Ca²⁺ is removed by the SERCA pump (into the SR), while ~25-28% is removed by the NCX.

Question 338: Plateau phase of cardiac muscle impulse conduction is due to the inward movement of?

A. Potassium ions (K+)
B. Sodium ions (Na+)
C. Calcium ions (Ca++) (Correct Answer)
D. Bicarbonate ions (HCO3-)

Explanation: ### Explanation The cardiac action potential in ventricular muscle fibers consists of five distinct phases (0-4). The **Plateau Phase (Phase 2)** is the characteristic feature that distinguishes cardiac muscle from skeletal muscle. **1. Why Calcium ions (Ca++) is correct:** During Phase 2, there is a prolonged period of depolarization. This is primarily due to the opening of **L-type (Long-lasting) Calcium channels**, leading to a slow **inward movement of Ca++ ions**. This influx is balanced by a slow outward movement of K+ ions, maintaining a relatively stable membrane potential (the "plateau"). This calcium entry is also crucial for **Excitation-Contraction Coupling**, as it triggers the release of more calcium from the sarcoplasmic reticulum (calcium-induced calcium release). **2. Why other options are incorrect:** * **Potassium ions (K+):** K+ efflux (outward movement) is responsible for **repolarization** (Phases 1, 2, and 3). It does not cause the plateau; rather, its balance with Ca++ maintains it. * **Sodium ions (Na+):** Rapid inward movement of Na+ through fast voltage-gated channels is responsible for **Phase 0 (Rapid Depolarization)**. * **Bicarbonate ions (HCO3-):** These ions are involved in acid-base balance and CO2 transport but do not play a direct role in the phases of the cardiac action potential. **3. NEET-PG High-Yield Pearls:** * **Phase 0:** Rapid Depolarization (Na+ influx). * **Phase 1:** Initial Rapid Repolarization (Closure of Na+ channels, transient K+ efflux). * **Phase 2:** Plateau (Ca++ influx via L-type channels). * **Phase 3:** Rapid Repolarization (K+ efflux). * **Phase 4:** Resting Membrane Potential (-90 mV). * **Clinical Significance:** Class IV antiarrhythmics (Calcium Channel Blockers like Verapamil) primarily act on Phase 2 of the action potential. The plateau phase ensures a long **Absolute Refractory Period**, preventing tetany in cardiac muscle.

Question 339: Which of the following statements regarding autoregulation is true?

A. It varies with changes in pressure.
B. It maintains blood flow. (Correct Answer)
C. It is well developed in the skin.
D. It is regulated by local metabolites.

Explanation: **Explanation:** **Autoregulation** is the intrinsic ability of an organ or tissue to maintain a relatively constant blood flow despite fluctuations in arterial perfusion pressure. 1. **Why Option B is Correct:** The primary physiological goal of autoregulation is to ensure that vital organs receive a steady supply of oxygen and nutrients. Within a specific range of mean arterial pressure (typically **70–175 mmHg**), the resistance of arterioles adjusts (via myogenic or metabolic mechanisms) to keep the **blood flow constant**. 2. **Why Other Options are Incorrect:** * **Option A:** Autoregulation aims to keep flow constant *despite* changes in pressure, not vary with it. If flow varied directly with pressure, autoregulation would be absent. * **Option C:** Autoregulation is **poorly developed in the skin**. Cutaneous blood flow is primarily regulated by the sympathetic nervous system for thermoregulation. It is **best developed** in the **Brain, Kidneys, and Heart**. * **Option D:** While local metabolites (like adenosine, CO₂, and H⁺) contribute to vasodilation (Metabolic Theory), the broader definition of autoregulation also includes the **Myogenic Mechanism** (Bayliss effect), where stretch-activated ion channels in smooth muscle respond to pressure changes. Therefore, saying it is regulated *only* by metabolites is incomplete compared to its functional definition (maintaining flow). **High-Yield NEET-PG Pearls:** * **Brain:** Most sensitive to CO₂ levels; maintains flow between 60–140 mmHg. * **Kidneys:** Primarily uses the **Tubuloglomerular Feedback (TGF)** mechanism. * **Heart:** Highly dependent on adenosine and local metabolic demand. * **Critical Range:** Below 60–70 mmHg, autoregulation fails, and flow becomes pressure-dependent (ischemia occurs).

Question 340: The velocity of blood flow is maximum in which of the following vessels?

A. Large arteries (Correct Answer)
B. Small arteries
C. Arterioles
D. Capillaries

Explanation: **Explanation:** The velocity of blood flow is governed by the principle of continuity, which states that velocity ($V$) is inversely proportional to the **total cross-sectional area** ($A$) of the vascular bed ($V = Q/A$, where $Q$ is blood flow/cardiac output). 1. **Large Arteries (Correct):** The aorta and large arteries have the smallest total cross-sectional area in the entire circulatory system. Because the entire cardiac output must pass through this narrow "pipe," the velocity is at its maximum (approx. 30–40 cm/sec in the aorta). 2. **Small Arteries & Arterioles:** As blood moves distally, the vessels branch. Although individual vessels are smaller, their **combined** total cross-sectional area increases, causing the velocity to decrease. 3. **Capillaries (Incorrect):** Capillaries have the largest total cross-sectional area (nearly 1000 times that of the aorta). Consequently, the velocity is at its **minimum** (approx. 0.03 cm/sec). This slow flow is physiologically essential to allow sufficient time for the exchange of gases and nutrients. **High-Yield Facts for NEET-PG:** * **Velocity vs. Area:** Velocity is lowest in capillaries; highest in the aorta. * **Pressure Profile:** The greatest **pressure drop** (highest resistance) occurs in the **arterioles**, not the capillaries. * **Blood Volume Distribution:** At any given time, the largest volume of blood (~64%) is contained within the **veins/venules** (capacitance vessels). * **Bernoulli’s Principle:** In a constricted vessel (like in stenosis), velocity increases while lateral pressure decreases.

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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