Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 631: In the cardiac cycle diagram, when does the first heart sound occur?

A. Point A (Correct Answer)
B. Point B
C. Point C
D. Point D

Explanation: ***Point A*** - The first heart sound (**S1**) occurs at the beginning of **ventricular systole** when the **mitral and tricuspid valves** close abruptly. - This valve closure prevents **backflow of blood** from the ventricles to the atria as ventricular pressure rises. *Point B* - Typically represents the **aortic valve opening** during ventricular systole, which is silent. - This occurs after S1 when **ventricular pressure** exceeds **aortic pressure**. *Point C* - Usually indicates the second heart sound (**S2**) caused by **aortic and pulmonary valve** closure. - This marks the end of ventricular systole and beginning of **diastole**. *Point D* - Often represents the **dicrotic notch** or events during **ventricular diastole**. - This occurs after S2 during the **filling phase** of the cardiac cycle.

Question 632: Regarding hemostasis, what is the true statement for nitric oxide?

A. Is a vasoconstrictor
B. Inhibits platelet activating factor-1
C. Inhibits Sinoatrial node
D. Inhibits platelet aggregation (Correct Answer)

Explanation: ### Explanation Nitric Oxide (NO), formerly known as Endothelium-Derived Relaxing Factor (EDRF), is a key gaseous signaling molecule produced by vascular endothelial cells. **Why Option D is Correct:** Nitric oxide plays a crucial role in maintaining vascular patency and preventing intravascular thrombosis. It diffuses into platelets and activates **soluble guanylyl cyclase**, which increases intracellular levels of **cyclic GMP (cGMP)**. Elevated cGMP leads to a decrease in intracellular calcium levels, which effectively **inhibits platelet adhesion and aggregation**. This ensures that the clotting process is localized only to the site of vascular injury and not spread across healthy endothelium. **Analysis of Incorrect Options:** * **Option A:** NO is a potent **vasodilator**, not a vasoconstrictor. It relaxes vascular smooth muscle via the cGMP pathway. * **Option B:** NO does not specifically target "Platelet Activating Factor-1." Its primary anti-thrombotic action is via cGMP-mediated inhibition of platelet activation and the expression of adhesion molecules (like P-selectin). * **Option C:** While NO has some modulatory effects on the autonomic nervous system, its primary physiological role in this context is vascular and hemostatic, not the inhibition of the SA node. **High-Yield Facts for NEET-PG:** * **Precursor:** NO is synthesized from the amino acid **L-arginine** by the enzyme **Nitric Oxide Synthase (NOS)**. * **Synergy:** NO works synergistically with **Prostacyclin ($PGI_2$)** to inhibit platelet aggregation. * **Clinical Correlation:** Nitroglycerin (used in Angina) works by being converted into Nitric Oxide, causing systemic vasodilation and reducing cardiac preload. * **Septic Shock:** Overproduction of NO by inducible NOS (iNOS) is a major cause of the profound vasodilation seen in septic shock.

Question 633: Which of the following conditions does not cause right axis deviation in ECG?

A. Lying down posture (Correct Answer)
B. End of deep inspiration
C. Right ventricular hypertrophy
D. Right bundle branch block

Explanation: **Explanation:** The electrical axis of the heart represents the average direction of depolarization. **Right Axis Deviation (RAD)** is defined as a QRS axis between +90° and +180°. **Why "Lying down posture" is the correct answer:** When a person moves from a standing to a **lying down (supine)** position, the abdominal viscera push the diaphragm upward. This physically shifts the heart into a more horizontal position, leading to a **Left Axis Deviation (LAD)**, not RAD. Conversely, standing causes the heart to become more vertical, leading to a rightward shift. **Analysis of Incorrect Options:** * **End of deep inspiration:** During deep inspiration, the diaphragm descends. This makes the heart more vertical (verticalization), causing the electrical axis to shift to the **right**. * **Right Ventricular Hypertrophy (RVH):** This is a classic cause of RAD. The increased muscle mass in the right ventricle generates greater electrical forces, pulling the mean QRS vector toward the right side. * **Right Bundle Branch Block (RBBB):** In RBBB, depolarization of the right ventricle is delayed. This late electrical activity occurs directed toward the right, resulting in a rightward shift of the mean axis. **High-Yield Clinical Pearls for NEET-PG:** * **Normal Axis:** -30° to +90°. * **RAD Causes:** Thin tall build, RVH, RBBB, Left Posterior Fascicular Block (LPFB), Pulmonary Embolism (S1Q3T3 pattern), and Lateral Wall MI. * **LAD Causes:** Obesity, Pregnancy, Ascites (all via diaphragm elevation), LVH, LBBB, and Left Anterior Fascicular Block (LAFB). * **Quick Rule:** If QRS is positive in Lead I and negative in aVF, it is LAD. If QRS is negative in Lead I and positive in aVF, it is RAD.

Question 634: Blood flow to the brain is not influenced by which of the following?

A. PaCO2
B. PaO2 (Correct Answer)
C. Cerebral circulation
D. Systemic circulation

Explanation: **Explanation:** The cerebral circulation is unique in its autoregulatory mechanisms, designed to maintain constant blood flow despite fluctuations in systemic pressure. **Why PaO2 is the correct answer:** Under normal physiological conditions, **PaO2 has little to no effect** on cerebral blood flow (CBF). CBF remains constant until PaO2 drops below a critical threshold of approximately **50 mmHg** (severe hypoxia). Only below this level does vasodilation occur to increase flow. Since the question implies normal physiological ranges, PaO2 is the least influential factor compared to the others. **Analysis of Incorrect Options:** * **PaCO2:** This is the **most potent physiological regulator** of CBF. An increase in PaCO2 (hypercapnia) causes marked cerebral vasodilation, while a decrease (hypocapnia) causes vasoconstriction. * **Cerebral Circulation:** Local factors such as metabolic products (H+, Adenosine, K+) and myogenic mechanisms directly control the resistance of cerebral vessels to maintain flow. * **Systemic Circulation:** While the brain autoregulates between a Mean Arterial Pressure (MAP) of **60–140 mmHg**, extreme changes in systemic circulation (e.g., shock or hypertensive crisis) will directly impact cerebral perfusion pressure (CPP = MAP - ICP). **High-Yield Pearls for NEET-PG:** 1. **CO2 Reactivity:** For every 1 mmHg rise in PaCO2, CBF increases by approximately 3-4%. 2. **Hyperventilation:** Clinically used in neurosurgery to lower PaCO2, causing vasoconstriction to reduce intracranial pressure (ICP). 3. **Monro-Kellie Doctrine:** The cranial vault is a fixed volume; an increase in blood, CSF, or brain tissue must be compensated by a decrease in the others to maintain pressure.

Question 635: What stimulates myocardial contraction?

A. Influx of Ca++ ions
B. Influx of Na+ ions (Correct Answer)
C. Efflux of K+ ions
D. Efflux of Na+ ions

Explanation: **Explanation:** The initiation of myocardial contraction is a result of **depolarization**, which is primarily triggered by the rapid **influx of Na+ ions**. In ventricular muscle fibers, the resting membrane potential is approximately -85 to -90 mV. When a stimulus reaches the cell, fast voltage-gated sodium channels open, leading to a massive influx of Na+ ions (Phase 0 of the action potential). This rapid shift in membrane potential toward a positive value is the electrical trigger that subsequently leads to the opening of L-type calcium channels and the "Calcium-Induced Calcium Release" (CICR) mechanism required for actual mechanical contraction. **Analysis of Options:** * **B. Influx of Na+ ions (Correct):** This represents Phase 0 (Depolarization). Without this initial sodium influx, the action potential cannot be generated to trigger the contractile machinery. * **A. Influx of Ca++ ions:** While Ca++ influx (Phase 2/Plateau phase) is essential for sustaining contraction and coupling excitation to contraction, it is the Na+ influx that *initiates* the electrical impulse in non-pacemaker myocardial cells. * **C. Efflux of K+ ions:** This occurs during Phase 1, 2, and 3 (Repolarization). It serves to reset the membrane potential to its resting state, thereby *ending* contraction. * **D. Efflux of Na+ ions:** This occurs via the Na+/K+ ATPase pump to maintain ionic gradients but does not stimulate contraction. **High-Yield NEET-PG Pearls:** * **Phase 0:** Rapid Depolarization (Na+ Influx). * **Phase 2 (Plateau):** Responsible for the long refractory period of cardiac muscle, preventing tetany (Ca++ Influx via L-type channels). * **Pacemaker Cells (SA Node):** Unlike the myocardium, the "pre-potential" or "pacemaker potential" is driven by **HCN channels (funny currents - Na+)** and **T-type Ca++ channels**, while the upstroke is due to **L-type Ca++ influx**, not Na+.

Question 636: Under normal conditions, the SA node acts as the pacemaker due to which of the following?

A. Slow depolarization, slow repolarization
B. Rapid depolarization, rapid repolarization
C. Slow depolarization, early repolarization (Correct Answer)
D. Rapid depolarization, delayed repolarization

Explanation: **Explanation:** The SA node is the physiological pacemaker of the heart because it possesses the highest intrinsic rate of firing (automaticity). This is primarily due to the unique characteristics of its action potential. **1. Why Option C is Correct:** The SA node exhibits **slow depolarization** (Phase 4), also known as the pacemaker potential. This is mediated by the "funny" sodium currents ($I_f$) and T-type calcium channels. This gradual rise toward the threshold ensures a rhythmic, spontaneous discharge. Furthermore, the SA node undergoes **early repolarization** (Phase 3) compared to other parts of the conduction system. Because it completes its recovery cycle faster than the AV node or Purkinje fibers, it reaches the threshold for the next beat first, thereby "overdrive suppressing" other potential pacemakers and maintaining control of the heart rate. **2. Why Other Options are Incorrect:** * **Options B & D (Rapid Depolarization):** Rapid depolarization (Phase 0) is a feature of **ventricular myocytes** and Purkinje fibers, mediated by fast sodium channels. The SA node lacks these channels and relies on slow L-type calcium channels for depolarization. * **Option A (Slow Repolarization):** If repolarization were slow, the refractory period would be prolonged, leading to a slower heart rate. The SA node must repolarize efficiently to initiate the next spontaneous depolarization cycle. **High-Yield NEET-PG Pearls:** * **Overdrive Suppression:** The mechanism by which the SA node inhibits slower latent pacemakers. * **Pre-potential (Phase 4):** The most critical phase for determining heart rate. Parasympathetic stimulation (ACh) decreases the slope of Phase 4, while Sympathetic stimulation (NE) increases it. * **Ionic Basis:** Phase 0 (Ca²⁺ influx), Phase 3 (K⁺ efflux), Phase 4 (Na⁺ influx via $I_f$ channels).

Question 637: A capillary that connects a metaeriole directly with a venule is called as?

A. Windkessel vessel
B. Resistance vessel
C. Exchange vessel
D. Thoroughfare vessel (Correct Answer)

Explanation: ### Explanation **1. Why the Correct Answer is Right:** The microcirculation consists of arterioles, capillaries, and venules. Within this network, a **metarteriole** acts as a transitional vessel. A **thoroughfare vessel** (or thoroughfare channel) is the distal continuation of a metarteriole that bypasses the true capillary bed and connects directly to a post-capillary venule. * **Mechanism:** When precapillary sphincters are constricted, blood is diverted away from the exchange network and flows directly through this "central channel" (metarteriole + thoroughfare vessel) to the venous side. This allows for rapid transit of blood without significant nutrient exchange. **2. Why the Other Options are Incorrect:** * **A. Windkessel vessel:** These are large elastic arteries (e.g., Aorta). They convert the intermittent, pulsatile output of the heart into a continuous flow through their elastic recoil properties. * **B. Resistance vessel:** These are primarily the **arterioles**. They have thick muscular walls and provide the greatest resistance to blood flow, thereby regulating systemic blood pressure. * **C. Exchange vessel:** These are the **true capillaries**. They lack smooth muscle and consist of a single layer of endothelial cells, specialized for the diffusion of gases, nutrients, and waste. **3. High-Yield Clinical Pearls for NEET-PG:** * **Capacitance Vessels:** Veins and venules (they hold ~60-70% of total blood volume). * **Precapillary Sphincters:** These are not found on thoroughfare vessels; they are located only at the origin of **true capillaries**. Their activity is primarily regulated by local metabolites (e.g., low $O_2$, high $CO_2$, low pH). * **Flow Regulation:** Blood flow through the metarteriole-thoroughfare channel is "vasomotion" (intermittent flow), which is a key physiological concept in tissue perfusion.

Question 638: Which of the following is a better predictor of vagal tone?

A. Basal heart rate (Correct Answer)
B. Ejection fraction
C. Stroke volume
D. LVET

Explanation: **Explanation:** **1. Why Basal Heart Rate is the Correct Answer:** The heart possesses intrinsic rhythmicity (the SA node naturally fires at ~100 bpm). However, in a resting state, the parasympathetic nervous system (vagus nerve) exerts a continuous inhibitory influence known as **vagal tone**. This "vagal brake" slows the heart rate down to the typical resting range of 60–80 bpm. Therefore, the **Basal Heart Rate** is the most direct clinical reflection of this parasympathetic activity. A lower basal heart rate (in the absence of pathology) typically indicates higher vagal tone, a common finding in endurance athletes. **2. Why Other Options are Incorrect:** * **B. Ejection Fraction (EF):** This is a measure of systolic function (Stroke Volume/End-Diastolic Volume). It is primarily influenced by myocardial contractility and afterload, not autonomic vagal tone. * **C. Stroke Volume (SV):** This is the volume of blood pumped per beat. While SV increases if the heart rate is slow (due to increased filling time), it is fundamentally a measure of ventricular performance and preload (Frank-Starling law), rather than a direct predictor of neural vagal input. * **D. LVET (Left Ventricular Ejection Time):** This is the interval from the opening to the closing of the aortic valve. It is influenced by heart rate and stroke volume but is used more to assess valvular function (e.g., aortic stenosis) and contractility rather than autonomic tone. **Clinical Pearls for NEET-PG:** * **Atropine Effect:** Administration of Atropine (a vagolytic) increases the heart rate to its intrinsic rate (~100 bpm) by blocking vagal tone. * **HRV (Heart Rate Variability):** While basal HR is a good predictor, HRV is considered the most sensitive non-invasive marker of autonomic balance in modern physiology. * **Vagal Maneuvers:** Carotid sinus massage or the Valsalva maneuver are used clinically to increase vagal tone to terminate Supraventricular Tachycardia (SVT).

Question 639: In the presence of a drug that blocks all effects of norepinephrine and epinephrine on the heart, the autonomic nervous system can:

A. Raise the heart rate above its intrinsic rate
B. Lower the heart rate below its intrinsic rate (Correct Answer)
C. Raise and lower the heart rate above and below its intrinsic rate
D. Neither raise nor lower the heart rate from its intrinsic rate

Explanation: **Explanation:** The heart rate is regulated by the dual influence of the autonomic nervous system (ANS): the **Sympathetic Nervous System (SNS)** and the **Parasympathetic Nervous System (PNS)**. 1. **Why Option B is Correct:** The sympathetic influence on the heart is mediated by **Norepinephrine** (from sympathetic nerves) and **Epinephrine** (from the adrenal medulla) acting primarily on **$\beta_1$-adrenergic receptors**. If a drug blocks all effects of these catecholamines, the sympathetic "accelerator" is effectively disabled. However, the parasympathetic influence, mediated by the **Vagus nerve** releasing **Acetylcholine** on **Muscarinic ($M_2$) receptors**, remains intact. Since the Vagus nerve acts to slow the heart rate, the ANS can still lower the heart rate below its intrinsic level (the rate at which the SA node fires without any neural input). 2. **Why Other Options are Incorrect:** * **Option A & C:** These are incorrect because raising the heart rate above the intrinsic rate requires sympathetic stimulation. Since the drug blocks norepinephrine and epinephrine, the SNS cannot increase the firing rate of the SA node. * **Option D:** This is incorrect because it ignores the functional parasympathetic pathway. The heart rate would only stay fixed at the intrinsic rate if *both* sympathetic and parasympathetic systems were blocked (pharmacological denervation). **High-Yield Clinical Pearls for NEET-PG:** * **Intrinsic Heart Rate:** In a healthy young adult, the intrinsic heart rate is approximately **100–110 bpm**. * **Vagal Tone:** Under resting conditions, the heart is under dominant parasympathetic (vagal) tone, which keeps the resting heart rate around **70–80 bpm**. * **Atropine Effect:** Atropine blocks $M_2$ receptors. If administered, it removes the "vagal brake," causing the heart rate to rise toward its intrinsic rate. * **Propranolol + Atropine:** This combination results in "complete autonomic blockade," revealing the true intrinsic firing rate of the SA node.

Question 640: Vitamin K is involved in the post-translational modification of which of the following coagulation factors?

A. Factor II
B. Factor X
C. Factor I (Correct Answer)
D. Protein C

Explanation: **Explanation** The question asks for the factor involved in Vitamin K-dependent post-translational modification. However, there appears to be a discrepancy in the provided key, as **Factor I (Fibrinogen) is NOT Vitamin K-dependent.** In standard medical teaching, Vitamin K is essential for the synthesis of Factors **II, VII, IX, X**, and **Proteins C and S**. **1. The Underlying Concept (Vitamin K Cycle):** Vitamin K acts as a cofactor for the enzyme **gamma-glutamyl carboxylase**. This enzyme performs the post-translational modification of glutamic acid residues into **gamma-carboxyglutamic acid (Gla)** on specific coagulation factors. This modification allows these proteins to bind calcium ions ($Ca^{2+}$), which is essential for their attachment to phospholipid membranes during the coagulation cascade. **2. Analysis of Options:** * **Factor I (Fibrinogen):** This is a soluble plasma glycoprotein synthesized in the liver. Its conversion to fibrin is mediated by thrombin. It does **not** undergo gamma-carboxylation and is not Vitamin K-dependent. (Note: If this is the "correct" answer in a specific mock test, it is likely a typographical error in the source material). * **Factor II (Prothrombin) & Factor X:** These are classic Vitamin K-dependent procoagulants. They require gamma-carboxylation to become functional. * **Protein C:** This is a Vitamin K-dependent **anticoagulant**. It degrades Factors Va and VIIIa. **3. NEET-PG High-Yield Pearls:** * **Mnemonic:** "1972" (Factors **10, 9, 7, 2**) + Proteins **C** and **S**. * **Warfarin Mechanism:** Inhibits **Vitamin K Epoxide Reductase (VKOR)**, preventing the recycling of Vitamin K, thereby inhibiting the carboxylation of these factors. * **Monitoring:** Warfarin therapy is monitored using **PT/INR** (reflecting Factor VII, which has the shortest half-life). * **Antidote:** For immediate reversal of Warfarin, use **Fresh Frozen Plasma (FFP)** or Prothrombin Complex Concentrate (PCC); for non-emergent reversal, use Vitamin K.

Practice by Chapter

Cardiac Electrophysiology

Practice Questions

Cardiac Cycle

Practice Questions

Cardiac Output and Its Regulation

Practice Questions

Hemodynamics and Blood Flow

Practice Questions

Arterial System Physiology

Practice Questions

Microcirculation and Lymphatics

Practice Questions

Venous Return and Central Venous Pressure

Practice Questions

Cardiovascular Reflexes

Practice Questions

Regional Circulations

Practice Questions

Cardiovascular Responses to Exercise and Stress

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free