Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 101: What organ has the greatest resting arteriovenous difference in oxygen content?

A. Heart (Correct Answer)
B. Kidney
C. Brain
D. Skeletal muscles

Explanation: **Explanation:** The **Arteriovenous (A-V) oxygen difference** represents the amount of oxygen extracted by an organ from the blood. The **Heart** has the highest resting A-V oxygen difference because it has the highest oxygen extraction ratio of any organ in the body. 1. **Why the Heart is Correct:** Under resting conditions, the myocardium extracts approximately **70-80%** of the oxygen delivered to it (A-V difference of ~11-15 ml/dL). Because the extraction is already near-maximal at rest, the heart cannot significantly increase oxygen extraction during periods of high demand (like exercise). Instead, it must rely almost entirely on **increasing coronary blood flow** to meet increased metabolic needs. 2. **Why the Other Options are Incorrect:** * **Kidney:** Has the lowest A-V oxygen difference (~1.5 ml/dL). Although it consumes significant oxygen, its blood flow is disproportionately high for its metabolic needs to facilitate filtration. * **Brain:** Has a high metabolic rate but a moderate A-V difference (~6 ml/dL), extracting about 25-30% of delivered oxygen. * **Skeletal Muscle:** At rest, the A-V difference is low (~5 ml/dL). However, during **strenuous exercise**, skeletal muscle can surpass the heart's extraction rate, but the question specifies "resting" conditions. **High-Yield NEET-PG Pearls:** * **Coronary Sinus:** The blood in the coronary sinus has the lowest oxygen saturation in the entire body (~25-30%). * **Adenosine:** The primary local metabolic vasodilator that increases coronary blood flow in response to hypoxia. * **Flow-Limited:** Since oxygen extraction is maximal at rest, myocardial oxygen consumption is "flow-limited," not "extraction-limited."

Question 102: CVP denotes the pressure of which chamber?

A. Left ventricle
B. Left atrium
C. Right ventricle
D. Right atrium (Correct Answer)

Explanation: **Explanation:** **Central Venous Pressure (CVP)** is defined as the pressure measured in the central veins close to the heart, specifically the superior vena cava. Because there are no valves between the central veins and the heart, CVP is considered a direct reflection of the **Right Atrial Pressure (RAP)**. 1. **Why Right Atrium is Correct:** The right atrium receives deoxygenated blood from the systemic circulation via the vena cavae. CVP serves as an estimate of right ventricular end-diastolic pressure (in the absence of tricuspid stenosis) and is a key indicator of venous return and intravascular volume status. 2. **Why Other Options are Incorrect:** * **Left Ventricle & Left Atrium:** These represent the "left-sided" pressures. Left atrial pressure is clinically estimated using **Pulmonary Capillary Wedge Pressure (PCWP)**, not CVP. * **Right Ventricle:** While CVP influences right ventricular filling, the pressure within the ventricle during systole is significantly higher than the CVP. CVP only equals right ventricular pressure during diastole when the tricuspid valve is open. **NEET-PG High-Yield Pearls:** * **Normal Range:** 2–8 mmHg (or 3–11 cm $H_2O$). * **Reference Point:** The zero point for CVP measurement is the **phlebostatic axis** (4th intercostal space, mid-axillary line). * **Waveforms:** Remember the "a" wave (atrial contraction), "c" wave (tricuspid bulging/ventricular contraction), and "v" wave (venous filling). * **Clinical Use:** A low CVP typically indicates hypovolemia, while a high CVP may suggest fluid overload, right heart failure, or cardiac tamponade.

Question 103: What is the initial mechanism by which lymphatic vessels clear excess fluid from interstitial tissue spaces?

A. Creating a lower hydrostatic pressure within the lymphatic vessel compared to the surrounding tissue. (Correct Answer)
B. Contracting to propel lymph into larger lymphatic vessels.
C. Utilizing one-way valves that open and close within the lymph vessels.
D. Reducing the colloid osmotic pressure inside the lymphatic vessel.

Explanation: ### Explanation **1. Why Option A is Correct:** The entry of fluid into the lymphatic system is governed by a **pressure gradient**. For interstitial fluid to move into the initial lymphatic capillaries, the **hydrostatic pressure** inside the lymphatic vessel must be lower than the hydrostatic pressure of the surrounding interstitial fluid. This is achieved through **anchoring filaments** that connect the lymphatic endothelial cells to the surrounding connective tissue. When excess fluid accumulates in the interstitium, the tissue swells, pulling these filaments. This action physically pulls the lymphatic endothelial junctions open and expands the vessel lumen, momentarily creating a **negative (sub-atmospheric) pressure** relative to the tissue, which "sucks" the fluid into the lymphatic capillary. **2. Why Other Options are Incorrect:** * **Option B:** Contraction (via smooth muscle in larger lymphatics or skeletal muscle pumps) is the mechanism for **propelling** lymph forward, not the *initial* mechanism of fluid entry into the capillaries. * **Option C:** One-way valves (semilunar valves) are crucial for ensuring **unidirectional flow** and preventing backflow, but they do not create the initial gradient required for fluid uptake. * **Option D:** Reducing colloid osmotic pressure would actually decrease the inward movement of fluid. Lymph typically has a higher protein concentration than plasma filtrate, which helps "hold" fluid once it enters, but hydrostatic pressure is the primary driver for initial clearance. **3. NEET-PG High-Yield Pearls:** * **Anchoring Filaments:** Composed of fibrillin; they are the structural key to opening lymphatic junctions during tissue edema. * **Lymphatic Pump:** Once inside, lymph is moved by the "intrinsic pump" (contraction of lymphangions) and "extrinsic pump" (skeletal muscle contraction and arterial pulsations). * **Starling Forces:** Lymphatic flow increases significantly when interstitial fluid pressure rises from negative values toward 0 mmHg or positive values. * **Thoracic Duct:** The largest lymphatic vessel, draining 75% of the body’s lymph into the left subclavian vein.

Question 104: Carbon monoxide poisoning is a type of which of the following?

A. Anemic hypoxia (Correct Answer)
B. Histotoxic hypoxia
C. Hypoxic hypoxia
D. Stagnant hypoxia

Explanation: **Explanation:** **Why Anemic Hypoxia is Correct:** Anemic hypoxia is defined as a condition where the arterial $PO_2$ is normal, but the **oxygen-carrying capacity** of the blood is reduced. In Carbon Monoxide (CO) poisoning, CO binds to hemoglobin with an affinity approximately **210–250 times greater** than oxygen, forming carboxyhemoglobin. This reduces the amount of hemoglobin available to carry oxygen. Furthermore, CO causes a **leftward shift of the Oxygen-Hemoglobin Dissociation Curve**, meaning the remaining oxygen binds more tightly to hemoglobin and is not easily released to the tissues. Despite normal dissolved oxygen (normal $PaO_2$), the total oxygen content is severely decreased, fitting the definition of anemic hypoxia. **Why Other Options are Incorrect:** * **Hypoxic Hypoxia:** Characterized by low arterial $PO_2$. This occurs at high altitudes or in pulmonary diseases where oxygen cannot enter the blood. In CO poisoning, $PaO_2$ remains normal. * **Stagnant (Ischemic) Hypoxia:** Occurs due to slow circulation or reduced blood flow (e.g., heart failure, shock). The blood has oxygen, but it isn't reaching tissues fast enough. * **Histotoxic Hypoxia:** Occurs when tissues cannot utilize oxygen despite adequate delivery (e.g., **Cyanide poisoning**, which inhibits Cytochrome Oxidase). **High-Yield Clinical Pearls for NEET-PG:** * **Cherry-red skin discoloration** is a classic (though often post-mortem) sign of CO poisoning. * **Pulse Oximetry (SpO2)** is notoriously unreliable in CO poisoning because standard sensors cannot distinguish between oxyhemoglobin and carboxyhemoglobin, often giving falsely high readings. * **Treatment:** 100% Oxygen (reduces CO half-life from 5 hours to ~80 mins) or Hyperbaric Oxygen.

Question 105: What is the major ion responsible for depolarization in Purkinje fibers?

A. Na+ (Correct Answer)
B. Ca++
C. K+
D. Cl-

Explanation: **Explanation:** The cardiac action potential varies significantly between different types of cardiac tissue. To answer this question, one must distinguish between **Fast-response action potentials** and **Slow-response action potentials**. **1. Why Na+ is Correct:** Purkinje fibers, along with atrial and ventricular myocytes, exhibit a **Fast-response action potential**. The rapid depolarization phase (Phase 0) is caused by the sudden opening of **voltage-gated fast Na+ channels**, leading to a rapid influx of sodium ions into the cell. This results in a steep upstroke velocity ($V_{max}$), which is essential for the rapid conduction of impulses throughout the ventricular conduction system. **2. Why the other options are incorrect:** * **B. Ca++:** Calcium is the major ion responsible for depolarization in **Slow-response tissues** (SA node and AV node). In Purkinje fibers, calcium influx occurs during the Plateau phase (Phase 2), not the initial depolarization. * **C. K+:** Potassium is primarily responsible for **repolarization** (Phases 1, 2, and 3). The efflux of K+ moves the membrane potential back toward a negative resting state. * **D. Cl-:** Chloride ions play a minor role in the early brief repolarization (Phase 1) in some cardiac cells but do not contribute to depolarization. **High-Yield Clinical Pearls for NEET-PG:** * **Conduction Velocity:** Purkinje fibers have the **fastest conduction velocity** (approx. 4 m/s) in the heart, ensuring synchronous ventricular contraction. * **Automaticity:** While the SA node is the primary pacemaker, Purkinje fibers act as tertiary pacemakers (intrinsic rate: 15–40 bpm) if higher centers fail. * **Phase 4:** In Purkinje fibers, Phase 4 is nearly flat, whereas in the SA node, Phase 4 has a spontaneous upward drift (pacemaker potential) due to $I_f$ (funny) currents.

Question 106: Which of the following is true of Endothelins?

A. Secreted by endothelium (Correct Answer)
B. Most potent vasoconstrictor
C. Both
D. None

Explanation: **Explanation:** **1. Why Option A is correct:** Endothelins are a family of potent vasoconstrictor peptides (ET-1, ET-2, and ET-3). **Endothelin-1 (ET-1)** is the most biologically relevant isoform in humans. It is synthesized and secreted primarily by **vascular endothelial cells** in response to stimuli such as thrombin, epinephrine, and shear stress. It acts locally (paracrine) on smooth muscle cells via $ET_A$ and $ET_B$ receptors to cause profound vasoconstriction. **2. Why Option B is technically incorrect in this context:** While Endothelin-1 is often described as the most potent *endogenous* vasoconstrictor, it is **not the most potent vasoconstrictor overall**. In pharmacological and physiological comparisons, **Urotensin II** (a somatostatin-like peptide) has been identified as the most potent vasoconstrictor known in humans, being roughly 8–10 times more potent than Endothelin-1. Therefore, in a competitive MCQ setting, "Secreted by endothelium" is the absolute physiological fact, whereas "Most potent" is a relative term often superseded by Urotensin II. **3. Why Option C and D are incorrect:** Since Option B is factually contested by Urotensin II, Option C (Both) becomes incorrect. Option D is incorrect because the endothelial origin of endothelins is a fundamental physiological principle. **High-Yield Clinical Pearls for NEET-PG:** * **Most Potent Vasoconstrictor:** Urotensin II > Endothelin-1 > Angiotensin II > Vasopressin. * **Receptors:** $ET_A$ (on smooth muscle → Vasoconstriction); $ET_B$ (on endothelium → NO release/Vasodilation; on smooth muscle → Vasoconstriction). * **Clinical Correlation:** **Bosentan** is a dual $ET_A$ and $ET_B$ receptor antagonist used in the treatment of Pulmonary Arterial Hypertension (PAH). * **Inhibitor:** Endothelin-converting enzyme (ECE) converts pro-endothelin to active ET-1.

Question 107: Dicumarol is a drug that impairs the utilization of vitamin K by the liver. Dicumarol therapy, therefore, would decrease the plasma concentration of which of the following procoagulants?

A. Prothrombin (Correct Answer)
B. Fibrinogen
C. Factor XI
D. Ac-globulin (factor V)

Explanation: **Explanation:** **1. Why Prothrombin (Factor II) is correct:** Dicumarol is a competitive inhibitor of Vitamin K epoxide reductase, similar to Warfarin. Vitamin K is a vital cofactor for the post-translational **gamma-carboxylation** of glutamic acid residues on specific clotting factors. This process is essential for these factors to bind calcium and phospholipids to become active. The Vitamin K-dependent factors are **Factors II (Prothrombin), VII, IX, and X**, as well as Proteins C and S. By impairing Vitamin K utilization, Dicumarol leads to the production of inactive precursors and a significant decrease in the plasma concentration of functional Prothrombin. **2. Why the other options are incorrect:** * **Fibrinogen (Factor I):** It is synthesized by the liver but does not require Vitamin K for its synthesis or activation. * **Factor XI (Plasma Thromboplastin Antecedent):** This factor is part of the intrinsic pathway but is not Vitamin K-dependent. * **Ac-globulin (Factor V):** Also known as Proaccelerin, it is a cofactor in the prothrombinase complex. While synthesized in the liver, its production is independent of Vitamin K. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic:** Remember Vitamin K-dependent factors as "**1972**" (Factors **10, 9, 7, and 2**). * **Monitoring:** The effect of Dicumarol/Warfarin is monitored using **Prothrombin Time (PT)** and **INR**, as Factor VII has the shortest half-life and is affected first. * **Antidote:** In case of overdose, the immediate treatment is **Fresh Frozen Plasma (FFP)** or Prothrombin Complex Concentrate (PCC) for rapid reversal, and **Vitamin K** for sustained recovery. * **Site of Action:** Gamma-carboxylation occurs in the **Rough Endoplasmic Reticulum** of hepatocytes.

Question 108: The vasomotor center of the medulla is associated with what function?

A. Acts with the cardiovagal center to maintain blood pressure. (Correct Answer)
B. Is independent of cortico-hypothalamic inputs.
C. Is influenced by baroreceptors but not chemoreceptors.
D. Is essentially silent during sleep.

Explanation: ### Explanation The **Vasomotor Center (VMC)**, located bilaterally in the reticular substance of the medulla and lower third of the pons, is the primary control center for blood pressure regulation. **Why Option A is Correct:** The VMC maintains blood pressure through a coordinated effort with the **Cardiovagal Center** (Nucleus Ambiguus and Dorsal Motor Nucleus of Vagus). While the VMC increases blood pressure via sympathetic outflow (vasoconstriction and increased heart rate), the cardiovagal center decreases it via parasympathetic (vagal) tone. The **Nucleus Tractus Solitarius (NTS)** acts as the sensory integration hub, receiving input from baroreceptors and modulating both centers to maintain hemodynamic stability. **Why Other Options are Incorrect:** * **Option B:** The VMC is **highly dependent** on higher centers. The hypothalamus (especially the posterior and lateral areas) and the cerebral cortex (limbic system) exert powerful excitatory or inhibitory effects on the VMC during stress, exercise, or emotional states. * **Option C:** The VMC is influenced by **both** baroreceptors (pressure-sensitive) and chemoreceptors (sensitive to $O_2$, $CO_2$, and $pH$). Chemoreceptors stimulate the VMC primarily when MAP falls below 80 mmHg to prevent hypoxia. * **Option D:** The VMC is **never silent**. It maintains a continuous state of partial contraction in blood vessels known as **sympathetic vasoconstrictor tone**, even during sleep, though its activity levels may fluctuate. ### High-Yield Clinical Pearls for NEET-PG * **Location:** The VMC consists of the C1 (vasopressor) and A1 (vasodepressor) areas. * **CNS Ischemic Response:** This is the most powerful activator of the VMC, triggered when cerebral blood flow decreases drastically (MAP < 60 mmHg). * **Cushing Reflex:** A specific type of CNS ischemic response where increased intracranial pressure leads to a triad of **Hypertension, Bradycardia, and Irregular Respiration.**

Question 109: Ventricular depolarization starts from which area?

A. Posterolateral area of ventricle
B. Base of left ventricle
C. Right part of interventricular septum
D. Left part of interventricular septum (Correct Answer)

Explanation: **Explanation:** The sequence of ventricular depolarization is a high-yield concept in cardiac physiology. The process begins when the impulse travels down the Bundle of His and enters the bundle branches. **Why Option D is Correct:** Ventricular depolarization initiates at the **middle third of the left side of the interventricular septum**. This occurs because the **Left Bundle Branch (LBB)** depolarizes slightly before the Right Bundle Branch. Consequently, the initial vector of depolarization moves from the **left toward the right** across the septum. This specific direction is responsible for the "septal q-wave" often seen in lateral ECG leads (I, aVL, V5, V6). **Analysis of Incorrect Options:** * **Option A (Posterolateral area):** This is one of the **last** areas to depolarize. The impulse travels from the endocardium to the epicardium, reaching the posterolateral walls after the septum and apex. * **Option B (Base of left ventricle):** Along with the pulmonary conus, the posterobasal portion of the left ventricle is the **final part** of the heart to undergo depolarization. * **Option C (Right part of septum):** Depolarization moves *toward* the right side, but it *originates* from the left side. **NEET-PG High-Yield Pearls:** 1. **Sequence of Depolarization:** Septum (Left to Right) → Apex/Major Ventricular Mass (Endocardium to Epicardium) → Base of the Heart. 2. **Sequence of Repolarization:** Epicardium to Endocardium (opposite to depolarization). This is why the T-wave is normally upright in leads with a tall R-wave. 3. **Septal Q-wave:** A small, initial downward deflection in lateral leads representing normal left-to-right septal activation. Its absence or exaggeration can indicate pathology (e.g., LBBB or MI).

Question 110: A decrease in blood pressure causes which of the following responses?

A. Inhibition of the vasoconstrictor center
B. Dis-inhibition of the vasoconstrictor center (Correct Answer)
C. Increased stimulation of the cardiac inhibitory center
D. Increased vagal stimulation

Explanation: ### Explanation The regulation of blood pressure is primarily mediated by the **Baroreceptor Reflex**. Baroreceptors are stretch receptors located in the carotid sinus and aortic arch. **Why Option B is Correct:** When blood pressure decreases, there is less stretch on the baroreceptors, leading to a **decrease in the firing rate** of the carotid sinus nerve (Hering’s nerve) and the glossopharyngeal nerve. Under normal conditions, these nerves stimulate the Nucleus Tractus Solitarius (NTS), which in turn inhibits the **Vasoconstrictor Center** (located in the Rostral Ventrolateral Medulla - RVLM). When the inhibitory signal from the NTS weakens due to low BP, the vasoconstrictor center is "released" from its usual inhibition. This process is called **dis-inhibition**. This leads to increased sympathetic outflow, causing vasoconstriction and increased heart rate to restore BP. **Why Other Options are Incorrect:** * **Option A:** Inhibition of the vasoconstrictor center occurs when BP is **high**, not low. * **Options C & D:** The Cardiac Inhibitory Center (NTS/Nucleus Ambiguus) mediates parasympathetic (vagal) tone. A decrease in BP leads to **decreased** stimulation of this center to allow the heart rate to rise (tachycardia). Increased vagal stimulation would further lower BP and heart rate. **High-Yield NEET-PG Pearls:** * **Receptor Location:** Carotid sinus (sensitive to both increase and decrease in BP) vs. Aortic arch (sensitive mainly to increases in BP). * **Afferents:** Carotid sinus via CN IX (Glossopharyngeal); Aortic arch via CN X (Vagus). * **The "Buffer" Nerve:** The baroreceptor nerves are called "buffer nerves" because they oppose both upward and downward drifts in arterial pressure. * **Inverse Relationship:** Firing rate of baroreceptors is directly proportional to BP, but the resulting sympathetic output is inversely proportional to the firing rate.

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