Cardiovascular System Practice Questions

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

3:01. **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.

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

Calcium ions (Ca++). ### 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.

Q: Which of the following statements regarding autoregulation is true?

It maintains blood flow.. **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).

Q: During ventricular systole, atrioventricular valves open and semilunar valves close. The statement is?

False. ### Explanation **1. Why the statement is False:** Ventricular systole is the period of ventricular contraction. To ensure blood flows in the correct direction (from the ventricles into the great arteries), the pressure dynamics must change: * **AV Valves (Mitral and Tricuspid) Close:** As ventricular pressure rises above atrial pressure at the start of systole, the AV valves snap shut to prevent backflow (regurgitation) into the atria. This closure produces the **First Heart Sound (S1)**. * **Semilunar Valves (Aortic and Pulmonary) Open:** Once ventricular pressure exceeds the pressure in the aorta and pulmonary artery, these valves open to allow blood ejection. Therefore, the statement is exactly the opposite of physiological reality: during systole, AV valves are **closed** and semilunar valves are **open**. **2. Analysis of Incorrect Options:** * **Option A (True):** Incorrect because if AV valves were open during systole, blood would flow backward into the atria instead of the systemic/pulmonary circulation. * **Options C & D (Partially True/False):** These are distractors. In a normal cardiac cycle, the valve states are binary during the ejection phase of systole. There is no physiological phase where AV valves are open while semilunar valves are closed during systole. **3. High-Yield Clinical Pearls for NEET-PG:** * **Isovolumetric Contraction:** This is the earliest phase of systole where **all four valves are closed**. Pressure rises sharply, but volume remains constant. * **S1 vs. S2:** S1 (Lubb) marks the beginning of systole (AV closure); S2 (Dupp) marks the beginning of diastole (Semilunar closure). * **Pressure Gradient:** The Aortic valve opens when Left Ventricular pressure exceeds ~80 mmHg. * **Wiggers Diagram:** Always correlate valve movements with the pressure curves; the "c" wave in the atrial pressure tracing occurs due to the bulging of AV valves into the atria during isovolumetric contraction.

Q: Which of the following is an action of angiotensin II?

Systemic vasodilation. **Explanation** Angiotensin II is a potent multifunctional hormone and a central component of the Renin-Angiotensin-Aldosterone System (RAAS). **Why Option B is Correct:** Angiotensin II acts primarily on **AT1 receptors** located on vascular smooth muscle cells. Its most immediate and potent effect is **systemic vasoconstriction** of the arterioles. This increases Total Peripheral Resistance (TPR), thereby rapidly elevating systemic blood pressure. **Analysis of Incorrect Options:** * **Option A & C:** Angiotensin II is a powerful **vasoconstrictor**, not a vasodilator. In the kidneys, it preferentially constricts the **efferent arterioles** more than the afferent arterioles to maintain Glomerular Filtration Rate (GFR) during states of low perfusion. * **Option D:** While Angiotensin II does promote sodium reabsorption, its primary direct action in the kidney is on the **Proximal Convoluted Tubule (PCT)** via the Na+/H+ exchanger. However, in the context of "classic" rapid systemic actions, vasoconstriction is its hallmark physiological effect. (Note: If the question asks for its effect on the adrenal cortex, it stimulates **Aldosterone** release, which acts on the Distal Tubule/Collecting Duct). **NEET-PG High-Yield Pearls:** * **Potency:** Angiotensin II is roughly 40-80 times more potent than Noradrenaline in raising blood pressure. * **Receptor Specificity:** Most known cardiovascular effects (vasoconstriction, aldosterone release, thirst) are mediated by **AT1 receptors**. AT2 receptors generally oppose these actions (vasodilation). * **ACE Inhibitors/ARBs:** These are first-line antihypertensives because they block the production or action of Angiotensin II, preventing systemic vasoconstriction. * **Dipsogenic Effect:** Angiotensin II acts on the subfornical organ in the brain to stimulate the **thirst center**.

Q: Coronary blood flow is regulated by which of the following mechanisms?

Local metabolic activity and reflexes. **Explanation:** The primary determinant of coronary blood flow is **local metabolic demand** (autoregulation). The heart is a highly aerobic organ with a high basal oxygen extraction rate (70-80%). Therefore, any increase in myocardial work must be met by an increase in blood flow rather than increased extraction. **1. Why the Correct Answer is Right:** When myocardial activity increases, local metabolites—most importantly **Adenosine**, but also $K^+$, $H^+$, $CO_2$, and lactate—accumulate. These act as potent vasodilators on the coronary arterioles. This "Active Hyperemia" ensures that blood supply matches the oxygen demand. Additionally, mechanical factors (reflexes) play a role, though metabolic control is the dominant force. **2. Why the Other Options are Wrong:** * **A & B (Sympathetic System):** While the heart has sympathetic innervation, its direct effect is weak. Sympathetic stimulation causes vasoconstriction (via $\alpha$-receptors), but this is immediately overridden by "functional sympatholysis"—where the increased heart rate and contractility produce metabolites that cause profound vasodilation. * **D (Parasympathetic System):** Vagal stimulation has a negligible direct effect on coronary vascular tone. **Clinical Pearls for NEET-PG:** * **Phasic Flow:** Coronary blood flow to the **Left Ventricle** is maximum during **Early Diastole** and minimum during Isovolumetric Contraction (due to mechanical compression of subendocardial vessels). * **Right Ventricle:** Flow is more uniform throughout the cardiac cycle because RV pressures are lower. * **Adenosine:** It is the most important local metabolic regulator of coronary blood flow. * **Coronary Steal Phenomenon:** Potent vasodilators (like Dipyridamole) can divert blood away from ischemic zones toward non-ischemic zones, worsening ischemia.

Q: Which of the following special circulations has the widest range of blood flows as part of its contributions to both the regulation of systemic vascular resistance and the modification of resistance to suit the organ's metabolic needs?

Skeletal muscle. **Explanation:** The correct answer is **Skeletal muscle**. This is because skeletal muscle constitutes approximately 40% of total body mass and exhibits the most dramatic range of blood flow variation in the human body. 1. **Why Skeletal Muscle is Correct:** * **Metabolic Range:** At rest, muscle blood flow is low (approx. 2–5 mL/min/100g). However, during maximal exercise, it can increase up to **20–50 fold** (reaching 100+ mL/min/100g) due to active hyperemia and local metabolic factors (lactate, adenosine, K+). * **Systemic Regulation:** Because of its massive total volume, skeletal muscle vasculature is a primary determinant of **Systemic Vascular Resistance (SVR)**. Under sympathetic stimulation (α1 receptors), vasoconstriction in muscles can significantly increase blood pressure and shunt blood to vital organs. 2. **Why Other Options are Incorrect:** * **Cerebral:** The brain requires a constant, stable blood flow (approx. 50 mL/min/100g). It has the tightest **autoregulation** and shows very little variation in total flow, regardless of activity levels. * **Small & Large Intestine:** While splanchnic blood flow increases after a meal (post-prandial hyperemia), the range of variation (approx. 8–10 fold) is significantly narrower than that of skeletal muscle. **High-Yield NEET-PG Pearls:** * **Resting Tone:** Skeletal muscle has high intrinsic sympathetic tone; its removal causes immediate vasodilation. * **Capillary Recruitment:** The massive increase in flow during exercise is achieved not just by vasodilation, but by "recruiting" previously closed capillaries. * **Key Regulator:** At rest, sympathetic nerves control flow; during exercise, **local metabolic factors** override sympathetic control (Functional Sympatholysis).

Q: What is true regarding myocardial oxygen demand?

Directly proportional to the duration of systole. **Explanation:** Myocardial oxygen demand ($MVO_2$) is primarily determined by the energy required for ventricular contraction and the maintenance of wall tension. **Why Option C is Correct:** The duration of systole is a critical determinant of oxygen consumption. During systole, the heart performs its most energy-intensive work (isovolumetric contraction and ventricular ejection). The **Tension-Time Index (TTI)**, which is the area under the left ventricular pressure curve during systole, is a major correlate of $MVO_2$. Therefore, any increase in the duration of systole (e.g., in aortic stenosis) significantly increases oxygen demand. **Analysis of Incorrect Options:** * **Option A:** $MVO_2$ is **directly related** to heart rate. A higher heart rate increases the number of contractions per minute, leading to higher cumulative energy expenditure. * **Option B:** There is **no constant relation** to external work. The heart is "inefficient"; pressure work (overcoming afterload) consumes much more oxygen than volume work (cardiac output/stroke volume). This is why hypertensive patients have higher oxygen demands than athletes with high stroke volumes. * **Option D:** $MVO_2$ is **never negligible**. Even at rest, the heart has a high basal metabolic rate to maintain ionic gradients and internal basal metabolism, extracting 70-80% of oxygen from the blood (the highest extraction ratio in the body). **High-Yield NEET-PG Pearls:** 1. **Law of Laplace:** Wall Tension = (Pressure × Radius) / (2 × Wall Thickness). Increased wall tension is the #1 determinant of $MVO_2$. 2. **Oxygen Extraction:** Unlike other organs, the heart cannot increase oxygen extraction significantly during exercise (as it is already near maximum); it must increase **coronary blood flow** to meet demand. 3. **Most Energy Consuming Phase:** Isovolumetric contraction consumes the most oxygen relative to the work performed.

Q: Flare response in triple response occurs due to?

Vasodilation due to release of secondary mediators. The **Triple Response of Lewis** is a physiological reaction of the skin to firm stroking or mechanical injury. It consists of three stages: the Red Reaction, the Flare, and the Wheal. ### **Explanation of the Correct Answer** **Option A** is correct because the **Flare** (the spreading redness beyond the initial line of injury) is mediated by the **Axon Reflex**. When the skin is injured, sensory nerve endings are stimulated. The impulse travels orthodromically toward the spinal cord but also **antidromically** (backward) along collateral branches of the same sensory nerve. This triggers the release of **secondary mediators**, primarily **Substance P** and **Calcitonin Gene-Related Peptide (CGRP)**. These potent vasodilators act on local arterioles, causing them to dilate and create the characteristic spreading flush. ### **Analysis of Incorrect Options** * **Option B:** Chemotaxis and leucocyte adhesion are features of the late-phase inflammatory response and cellular migration, not the acute vascular changes seen in the triple response. * **Option C:** Direct vessel injury causes the initial **Red Reaction** (Stage 1), which is a localized capillary dilation due to mechanical stimulation, independent of the nerve supply. * **Option D:** Increased permeability leads to the **Wheal** (Stage 3). This is localized edema caused by histamine release from mast cells, increasing capillary permeability and leading to exudation of fluid. ### **High-Yield NEET-PG Pearls** * **Sequence:** Red Reaction (Capillary dilation) → Flare (Arteriolar dilation via Axon Reflex) → Wheal (Exudation/Edema). * **Mediator for Wheal:** Histamine. * **Mediator for Flare:** Substance P / CGRP (Axon Reflex). * **Clinical Note:** If the sensory nerve to the skin area is severed and allowed to degenerate, the **Flare response will be absent**, while the Red Reaction and Wheal may still occur.

Question 1

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

Accepted Answer

3:01

Answer

1:01

Answer

1:03

Answer

4:01

Question 2

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

Accepted Answer

Calcium ions (Ca++)

Answer

Potassium ions (K+)

Answer

Sodium ions (Na+)

Answer

Bicarbonate ions (HCO3-)

Question 3

Which of the following statements regarding autoregulation is true?

Accepted Answer

It maintains blood flow.

Answer

It varies with changes in pressure.

Answer

It is well developed in the skin.

Answer

It is regulated by local metabolites.

Question 4

During ventricular systole, atrioventricular valves open and semilunar valves close. The statement is?

Accepted Answer

False

Answer

True

Answer

Partially true

Answer

Partially false

Question 5

Which of the following is an action of angiotensin II?

Accepted Answer

Systemic vasodilation

Answer

Systemic vasoconstriction

Answer

Renal vasodilation

Answer

Reabsorption of sodium ions in the proximal renal tubule

Question 6

Coronary blood flow is regulated by which of the following mechanisms?

Accepted Answer

Local metabolic activity and reflexes

Answer

Sympathetic adrenergic system

Answer

Sympathetic cholinergic system

Answer

Parasympathetic system

Question 7

Which of the following special circulations has the widest range of blood flows as part of its contributions to both the regulation of systemic vascular resistance and the modification of resistance to suit the organ's metabolic needs?

Accepted Answer

Skeletal muscle

Answer

Large intestine

Answer

Cerebral

Answer

Small intestine

Question 8

Which of the following is a true statement about heart sounds S1 and S2?

Accepted Answer

S2 has a higher frequency but shorter duration compared to S1.

Answer

S1 has a higher frequency and longer duration than S2.

Answer

S2 has a higher frequency and longer duration than S1.

Answer

S1 has a higher frequency but shorter duration compared to S2.

Question 9

What is true regarding myocardial oxygen demand?

Accepted Answer

Directly proportional to the duration of systole

Answer

Inversely related to heart rate

Answer

Has a constant relation to external cardiac work

Answer

Is negligible at rest

Question 10

Flare response in triple response occurs due to?

Accepted Answer

Vasodilation due to release of secondary mediators

Answer

Chemotaxis and adhesion of leucocytes to vessel wall

Answer

Direct vessel injury

Answer

Increased permeability

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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