Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 371: Clamping of the carotid arteries below the carotid sinus is likely to produce what?

A. Increase in vasomotor center activity (Correct Answer)
B. Increase in discharge of carotid sinus afferent nerves
C. Decreased heart rate and blood pressure
D. Baroreceptor adaptation

Explanation: **Explanation:** The carotid sinus, located at the bifurcation of the common carotid artery, contains **baroreceptors** (stretch receptors) that monitor arterial blood pressure. These receptors send inhibitory signals via the **Hering’s nerve** (branch of Glossopharyngeal nerve, CN IX) to the Nucleus Tractus Solitarius (NTS) in the medulla. **Why Option A is correct:** When the carotid arteries are clamped **below** the sinus, blood flow to the sinus is cut off. This leads to a **decrease in transmural pressure** within the carotid sinus. The baroreceptors perceive this as a drop in systemic blood pressure. Consequently, the rate of afferent firing decreases, leading to "disinhibition" of the **Vasomotor Center (VMC)**. The VMC then increases sympathetic outflow, resulting in peripheral vasoconstriction, increased heart rate, and a rise in systemic blood pressure (the **Carotid Sinus Reflex**). **Why other options are incorrect:** * **Option B:** Clamping reduces pressure in the sinus; therefore, the discharge rate of afferent nerves **decreases**, not increases. * **Option C:** The reflex response to perceived hypotension is an **increase** in heart rate (tachycardia) and blood pressure (hypertension) to compensate. * **Option D:** Baroreceptor adaptation refers to the resetting of receptors to a higher baseline in chronic hypertension; it is not an acute response to clamping. **High-Yield NEET-PG Pearls:** * **Afferent Pathway:** Carotid Sinus → CN IX; Aortic Arch → CN X (Vagus). * **Location:** Carotid sinus is a dilatation of the **Internal Carotid Artery** just above the bifurcation. * **Clinical Correlation:** Carotid sinus massage mimics high pressure, stimulating the baroreceptors to increase vagal tone, which can terminate Paroxysmal Supraventricular Tachycardia (PSVT).

Question 372: Which of the following is NOT a function of blood plasma?

A. Transport of hormones
B. Transport of oxygen (Correct Answer)
C. Transport of antibodies
D. Transport of chylomicrons

Explanation: ### Explanation **1. Why "Transport of Oxygen" is the Correct Answer:** While a very small amount of oxygen (about 1.5% or 0.3 ml/dL) is dissolved physically in the plasma, the **primary and functional transport of oxygen** is the responsibility of **Hemoglobin** located within **Red Blood Cells (RBCs)**. In the context of physiological functions, oxygen transport is categorized as a cellular function rather than a plasma function. Plasma's role in gas transport is primarily focused on Carbon Dioxide (as bicarbonate ions). **2. Analysis of Incorrect Options:** * **A. Transport of Hormones:** Plasma serves as the primary vehicle for hormones. Water-soluble hormones (e.g., Catecholamines) travel freely, while lipid-soluble hormones (e.g., Steroids, Thyroid hormones) travel bound to specific plasma proteins like Albumin or Globulins. * **C. Transport of Antibodies:** Antibodies (Immunoglobulins) are specialized proteins synthesized by plasma cells and are found exclusively in the **gamma-globulin fraction** of the blood plasma. * **D. Transport of Chylomicrons:** After digestion, dietary lipids are packaged into chylomicrons by enterocytes. These enter the bloodstream via the thoracic duct and are transported through the plasma to reach the liver and adipose tissue. **3. NEET-PG High-Yield Pearls:** * **Plasma vs. Serum:** Plasma contains clotting factors (like Fibrinogen); Serum is Plasma minus the clotting factors. * **Oncotic Pressure:** Plasma proteins (mainly **Albumin**) maintain the Colloid Osmotic Pressure (~25-28 mmHg), which prevents edema. * **Buffering:** Plasma proteins act as an important blood buffer system due to their amphoteric nature (Zwitterions). * **Specific Gravity:** The specific gravity of plasma is approximately **1.022 to 1.026**, primarily determined by the concentration of plasma proteins.

Question 373: Rubor (redness) during inflammation is primarily due to:

A. Decreased tissue oncotic pressure
B. Decreased oncotic pressure in arterioles
C. Constriction of the capillaries
D. Dilatation of the arterioles (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Dilatation of the arterioles** **Mechanism:** The cardinal signs of inflammation (Rubor, Calor, Tumor, Dolor, and Functio Laesa) are initiated by chemical mediators like histamine, bradykinin, and prostaglandins. **Rubor (redness)** and **Calor (heat)** are primarily caused by **active hyperemia**. This occurs when inflammatory mediators cause the smooth muscles of the **arterioles** to relax, leading to vasodilation. This increases blood flow to the capillary bed, resulting in the characteristic redness and warmth seen in inflamed tissues. **Analysis of Incorrect Options:** * **A & B (Decreased Oncotic Pressure):** Oncotic pressure (primarily maintained by albumin) governs fluid movement between compartments. A decrease in oncotic pressure contributes to **Tumor (edema)** by allowing fluid to leak into the interstitium, but it does not cause the redness associated with Rubor. * **C (Constriction of the capillaries):** Capillaries lack smooth muscle and do not "constrict" in the traditional sense. Furthermore, any reduction in blood flow (vasoconstriction) would lead to pallor (whiteness), not rubor. **High-Yield Clinical Pearls for NEET-PG:** * **Triple Response of Lewis:** Includes **Flush** (capillary dilatation), **Flare** (arteriolar dilatation via axon reflex), and **Wheal** (exudation/edema). * **Sequence of Hemodynamic Changes:** Transient vasoconstriction (seconds) → Persistent arteriolar vasodilation → Increased vascular permeability (leading to stasis). * **Key Mediator:** Histamine is the most important mediator for the immediate transient phase of increased vascular permeability.

Question 374: What is the first event to occur due to activation of baroreceptors?

A. Inhibition of the rostral ventrolateral medulla
B. Stimulation of the nucleus tractus solitarius (Correct Answer)
C. Stimulation of the cardio-vagal center
D. Stimulation of the caudal ventrolateral medulla

Explanation: ### Explanation The baroreceptor reflex is the body's rapid-response mechanism for maintaining blood pressure homeostasis. **Why Option B is Correct:** When blood pressure rises, stretch receptors in the **carotid sinus** (via Glossopharyngeal nerve) and **aortic arch** (via Vagus nerve) are activated. These afferent fibers carry impulses directly to the **Nucleus Tractus Solitarius (NTS)** in the medulla. The NTS acts as the primary sensory relay station; therefore, its stimulation is the **obligatory first central event** in the reflex arc. **Analysis of Incorrect Options:** * **Option D (Stimulation of CVLM):** This occurs *after* the NTS is stimulated. The NTS sends excitatory glutamatergic projections to the Caudal Ventrolateral Medulla (CVLM). * **Option A (Inhibition of RVLM):** This is a downstream effect. The CVLM sends inhibitory GABAergic signals to the Rostral Ventrolateral Medulla (RVLM). The RVLM is the primary "pressor" area; its inhibition leads to decreased sympathetic outflow. * **Option C (Stimulation of cardio-vagal center):** Simultaneously with CVLM activation, the NTS stimulates the Nucleus Ambiguus and Dorsal Motor Nucleus of Vagus. While this occurs, it is secondary to the initial NTS activation. **NEET-PG High-Yield Pearls:** * **Afferent Pathways:** Carotid sinus = Hering’s nerve (CN IX); Aortic arch = Cyon’s nerve (CN X). * **The "Buffer" Nerves:** Baroreceptor nerves are called buffer nerves because they minimize BP fluctuations. Denervation leads to "empty baroreceptor" syndrome (labile hypertension). * **Sensitivity:** Baroreceptors are most sensitive to the **rate of change** in pressure rather than a constant mean pressure. * **Resetting:** In chronic hypertension, baroreceptors "reset" to a higher baseline, maintaining the high BP rather than correcting it.

Question 375: What is the effect of Angiotensin II?

A. Vasoconstriction (Correct Answer)
B. Vasodilation
C. Increased heart rate
D. Decreased heart rate

Explanation: **Explanation:** **Angiotensin II** is a potent octapeptide and a central component of the Renin-Angiotensin-Aldosterone System (RAAS). Its primary physiological effect is **potent vasoconstriction** (Option A). It acts directly on AT1 receptors located on vascular smooth muscle cells, leading to an increase in total peripheral resistance and a subsequent rise in arterial blood pressure. **Analysis of Options:** * **Option B (Vasodilation):** This is incorrect. Angiotensin II is one of the most powerful endogenous vasoconstrictors known. Vasodilation is typically mediated by substances like Nitric Oxide, Bradykinin, or ANP. * **Options C & D (Heart Rate):** Angiotensin II does not have a primary, direct chronotropic effect on the heart. While it can increase sympathetic outflow (potentially increasing HR) or cause a baroreceptor-mediated reflex bradycardia (decreasing HR) due to the sudden rise in blood pressure, these are secondary responses and not its direct mechanism of action. **High-Yield Clinical Pearls for NEET-PG:** 1. **Receptor Specificity:** Most known effects (vasoconstriction, aldosterone release, thirst) are mediated via **AT1 receptors**. AT2 receptors generally oppose these effects but are less dominant in adults. 2. **Adrenal Effect:** Angiotensin II stimulates the *Zona Glomerulosa* of the adrenal cortex to release **Aldosterone**, leading to sodium and water retention. 3. **Renal Effect:** It preferentially constricts the **efferent arteriole** of the glomerulus, which helps maintain the Glomerular Filtration Rate (GFR) when renal perfusion pressure is low. 4. **Pharmacology Link:** ACE Inhibitors (e.g., Enalapril) and ARBs (e.g., Losartan) are first-line antihypertensives because they block the production or action of Angiotensin II.

Question 376: What is preload?

A. End systolic volume
B. End diastolic volume (Correct Answer)
C. Peripheral resistance
D. Stroke volume

Explanation: **Explanation:** **Preload** is defined as the initial stretching of the cardiac myocytes (muscle cells) prior to contraction. In clinical practice, it represents the volume of blood present in the ventricles at the end of the filling phase. 1. **Why Option B is Correct:** **End-Diastolic Volume (EDV)** is the most accurate clinical surrogate for preload. According to the **Frank-Starling Law**, the force of heart contraction is directly proportional to the initial length of the muscle fiber. As EDV increases, the ventricular walls stretch more, increasing the preload and subsequently increasing the stroke volume (within physiological limits). 2. **Why Other Options are Incorrect:** * **Option A (End-Systolic Volume):** This is the volume of blood remaining in the ventricle *after* contraction. It does not represent the initial stretch. * **Option C (Peripheral Resistance):** This is a major component of **Afterload**, which is the resistance the heart must pump against to eject blood. * **Option D (Stroke Volume):** This is the volume of blood ejected per beat (EDV minus ESV). It is a *result* of preload, not the preload itself. **High-Yield Clinical Pearls for NEET-PG:** * **Factors increasing Preload:** Intravenous fluids, sympathetic stimulation (venoconstriction), and horizontal positioning. * **Factors decreasing Preload:** Diuretics (furosemide), nitrates (venodilators), and hemorrhage. * **Key Formula:** Stroke Volume = EDV – ESV. * **Relationship:** Preload ∝ Venous Return. If venous return increases, EDV (preload) increases.

Question 377: Elasticity of heart muscle mainly depends on which protein?

A. Myosin
B. Actin
C. Titin (Correct Answer)
D. Troponin

Explanation: **Explanation:** The correct answer is **Titin** (also known as connectin). **Why Titin is correct:** Titin is the largest known protein in the human body and acts as a molecular spring within the sarcomere. It extends from the Z-disc to the M-line, anchoring the thick filaments (myosin) in the center. Its primary physiological role is to provide **passive elasticity** and stiffness to the cardiac muscle. During diastole, as the heart fills with blood, titin molecules stretch; during systole, they recoil, contributing to the Frank-Starling mechanism by ensuring the sarcomere returns to its original length. **Why the other options are incorrect:** * **Myosin (Option A):** This is the primary protein of the **thick filament** responsible for the "power stroke" and active contraction (force generation), not passive elasticity. * **Actin (Option B):** This is the primary protein of the **thin filament**. It provides the binding sites for myosin heads during contraction but does not possess elastic properties. * **Troponin (Option D):** This is a regulatory protein complex (T, I, and C) that modulates the interaction between actin and myosin in response to calcium levels. It does not contribute to the structural elasticity of the muscle. **High-Yield NEET-PG Pearls:** * **Frank-Starling Law:** Titin is a major determinant of the length-tension relationship in the heart. * **Clinical Correlation:** Mutations in the *TTN* gene (encoding Titin) are the most common genetic cause of **Dilated Cardiomyopathy (DCM)**. * **Stiffness:** In Diastolic Heart Failure (HFpEF), alterations in titin phosphorylation can lead to increased myocardial stiffness. * **Size:** Remember Titin as the "giant" protein of the sarcomere.

Question 378: If the radius of a blood vessel is doubled, by how many times does the blood flow increase?

A. 8 times
B. 16 times (Correct Answer)
C. 32 times
D. 256 times

Explanation: ### Explanation **1. The Underlying Concept: Poiseuille’s Law** The correct answer is **16 times** because blood flow ($Q$) through a vessel is governed by **Poiseuille’s Law**. This law states that flow is directly proportional to the fourth power of the radius ($r^4$). The formula is: $Q \propto r^4$ When the radius is doubled ($r$ becomes $2r$), the new flow ($Q_{new}$) is calculated as: $Q_{new} \propto (2)^4$ $2 \times 2 \times 2 \times 2 = 16$ Therefore, doubling the radius increases the flow by a factor of 16. This highlights that the radius is the most powerful determinant of blood flow and vascular resistance. **2. Analysis of Incorrect Options** * **Option A (8 times):** This would occur if flow were proportional to $r^3$. This is a common calculation error where students confuse the exponent. * **Option C (32 times):** This would occur if flow were proportional to $r^5$. * **Option D (256 times):** This occurs if the radius is quadrupled ($4^4 = 256$), not doubled. **3. NEET-PG Clinical Pearls & High-Yield Facts** * **Resistance ($R$):** Resistance is inversely proportional to the fourth power of the radius ($R \propto 1/r^4$). If the radius doubles, resistance drops to **1/16th** of its original value. * **Arterioles as "Resistance Vessels":** Because of Poiseuille’s Law, small changes in the diameter of arterioles (via sympathetic tone) lead to massive changes in total peripheral resistance (TPR) and blood pressure. * **Series vs. Parallel:** Remember that adding resistance in **series** increases total resistance, while adding it in **parallel** (as seen in most organ systems) decreases total resistance. * **Viscosity:** Flow is inversely proportional to viscosity ($\eta$). In conditions like **Polycythemia**, increased viscosity significantly decreases blood flow.

Question 379: Which phase of the cardiac cycle follows immediately after the beginning of the QRS wave?

A. Isovolumic relaxation
B. Atrial systole
C. Diastasis
D. Isovolumic contraction (Correct Answer)

Explanation: **Explanation:** The cardiac cycle is a sequence of electrical and mechanical events. To answer this question, one must correlate the **Electrocardiogram (ECG)** with the mechanical phases of the heart. **Why Isovolumic Contraction is Correct:** The **QRS complex** represents **ventricular depolarization**. This electrical trigger leads to the onset of ventricular systole. The very first phase of ventricular systole is **isovolumic contraction**. During this phase, the ventricles begin to contract, causing intraventricular pressure to rise sharply. This pressure rise immediately closes the Atrioventricular (AV) valves (producing the **S1 heart sound**). Since the semilunar valves are not yet open, the ventricle contracts as a closed chamber with no change in volume. **Analysis of Incorrect Options:** * **Atrial Systole:** This corresponds to the **P wave** (atrial depolarization) on the ECG. It occurs before the QRS complex. * **Diastasis:** This is the phase of slow ventricular filling during diastole. It occurs long after the T wave and before the next P wave. * **Isovolumic Relaxation:** This occurs at the beginning of ventricular diastole, immediately following the closure of the semilunar valves (associated with the end of the **T wave**). **High-Yield NEET-PG Pearls:** * **S1 Heart Sound:** Occurs at the beginning of isovolumic contraction (just after the R wave peak). * **S2 Heart Sound:** Occurs at the beginning of isovolumic relaxation. * **Maximum Oxygen Consumption:** The heart consumes the most oxygen during the **isovolumic contraction phase** because it is generating high pressure against closed valves. * **c-wave (JVP):** Corresponds to isovolumic contraction (bulging of the tricuspid valve into the right atrium).

Question 380: Which of the following is NOT true regarding endothelin-1?

A. Bronchodilation (Correct Answer)
B. Vasoconstriction
C. Decreased GFR
D. Has inotropic effect

Explanation: **Explanation:** Endothelin-1 (ET-1) is a potent 21-amino acid peptide produced primarily by vascular endothelial cells. It acts via two main G-protein coupled receptors: **$ET_A$** (found on vascular smooth muscle, mediating contraction) and **$ET_B$** (found on both endothelium and smooth muscle). **Why Option A is the Correct Answer:** Endothelin-1 is a potent **bronchoconstrictor**, not a bronchodilator. It stimulates the contraction of airway smooth muscle and is often found in elevated levels in patients with asthma. Therefore, "Bronchodilation" is the false statement. **Analysis of Other Options:** * **B. Vasoconstriction:** ET-1 is one of the most powerful endogenous vasoconstrictors known (nearly 10 times more potent than Angiotensin II). It acts via $ET_A$ receptors to increase intracellular calcium in vascular smooth muscle. * **C. Decreased GFR:** In the kidneys, ET-1 causes profound afferent and efferent arteriolar vasoconstriction. This leads to a reduction in renal blood flow and a subsequent **decrease in Glomerular Filtration Rate (GFR)**. * **D. Has Inotropic Effect:** ET-1 exerts a significant **positive inotropic effect** on the myocardium and can also induce cardiac hypertrophy over time. **High-Yield NEET-PG Pearls:** * **Stimulus for Release:** ET-1 release is stimulated by Thrombin, Epinephrine, Angiotensin II, and low shear stress. It is inhibited by Nitric Oxide (NO) and Prostacyclin. * **Clinical Application:** **Bosentan** is a dual $ET_A$ and $ET_B$ receptor antagonist used in the treatment of **Pulmonary Arterial Hypertension (PAH)**. * **Marker:** It is often considered a marker of endothelial dysfunction.

Practice by Chapter

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