Cardiovascular System Practice Questions

Q: Cardiac output depends on all of the following except?

Body surface area. **Explanation:** The fundamental equation for cardiac output is **Cardiac Output (CO) = Stroke Volume (SV) × Heart Rate (HR)**. **Why Body Surface Area (BSA) is the correct answer:** Cardiac output is an absolute measurement of the volume of blood pumped by the heart per minute (typically ~5 L/min). While CO is often *normalized* to a person's body size to allow for clinical comparison between individuals of different sizes—a parameter known as the **Cardiac Index (CI = CO/BSA)**—the actual generation of cardiac output itself does not depend on the body surface area. BSA is a scaling factor used for interpretation, not a physiological determinant of the heart's pumping capacity. **Analysis of incorrect options:** * **Cardiac Rate (HR):** As per the formula (CO = SV × HR), any change in heart rate directly impacts the cardiac output. * **Stroke Volume (SV):** This is the volume of blood ejected per beat. It is a primary determinant of CO. * **Cardiac Contractility:** This is a major determinant of Stroke Volume (along with preload and afterload). Increased contractility (inotropy) increases the ejection fraction and stroke volume, thereby increasing cardiac output. **High-Yield Clinical Pearls for NEET-PG:** * **Cardiac Index (CI):** Normal range is **2.5 to 4.0 L/min/m²**. It is a more accurate indicator of whether the CO is sufficient for an individual's metabolic needs. * **Fick’s Principle:** The gold standard for measuring CO. $CO = \text{Oxygen Consumption} / (\text{Arterial } O_2 \text{ content} - \text{Mixed Venous } O_2 \text{ content})$. * **Preload:** According to the **Frank-Starling Law**, increased preload increases SV and thus CO, up to a physiological limit.

Q: What is the main role of angiotensin II?

Increased TPR. **Explanation:** Angiotensin II (AT-II) is a potent octapeptide and a central component of the Renin-Angiotensin-Aldosterone System (RAAS). Its primary physiological role is to maintain blood pressure and fluid balance. **1. Why "Increased TPR" is correct:** Angiotensin II is one of the most powerful direct **vasoconstrictors** known. It acts on **AT1 receptors** located on vascular smooth muscle cells throughout the systemic circulation. By causing widespread arteriolar constriction, it significantly increases **Total Peripheral Resistance (TPR)**, which directly raises the Mean Arterial Pressure (MAP = CO × TPR). **2. Analysis of Incorrect Options:** * **B. Constriction of afferent renal arteriole:** AT-II preferentially constricts the **efferent arteriole** more than the afferent. This increases glomerular capillary hydrostatic pressure, thereby maintaining the Glomerular Filtration Rate (GFR) even when renal blood flow is low. * **C. Decreased release of aldosterone:** AT-II actually **stimulates** the zona glomerulosa of the adrenal cortex to release aldosterone, which promotes sodium and water retention. * **D. Diuresis:** AT-II is **anti-diuretic** and **anti-natriuretic**. It promotes water and salt retention both directly (by stimulating Na+/H+ exchange in the proximal tubule) and indirectly (via aldosterone and ADH release). **High-Yield Clinical Pearls for NEET-PG:** * **Receptor Specificity:** Most known cardiovascular effects (vasoconstriction, thirst, aldosterone release) are mediated via **AT1 receptors**. AT2 receptors generally mediate vasodilation and anti-proliferation. * **ACE Inhibitors/ARBs:** These are first-line antihypertensives because they block the production or action of AT-II, leading to decreased TPR. * **Thirst Center:** AT-II acts on the subfornical organ in the brain to stimulate the thirst mechanism.

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

End-diastolic volume. ### 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).

Q: Endothelium-derived relaxing factor is:

Nitric oxide. **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.

Q: What is the effect of sympathetic stimulation?

Vasoconstriction of skin and mucus membranes. The sympathetic nervous system (SNS) is the "fight or flight" system, designed to redirect blood flow to vital organs and prepare the body for physical exertion. ### **Explanation of the Correct Answer** **D. Vasoconstriction of skin and mucus membranes:** This occurs via the stimulation of **$\alpha_1$-adrenergic receptors**. During sympathetic activation, the body shunts blood away from non-essential peripheral areas (like the skin and mucosa) toward the skeletal muscles, heart, and brain. This is why a person may appear pale during a "fight or flight" response. ### **Analysis of Incorrect Options** * **A. Pupillary constriction:** This is a **parasympathetic** effect (miosis) mediated by $M_3$ receptors. Sympathetic stimulation causes **pupillary dilation (mydriasis)** via $\alpha_1$ receptors on the radial dilator pupillae muscle. * **B. Contraction of bladder detrusor:** This is a **parasympathetic** effect ($M_3$) to facilitate voiding. Sympathetic stimulation causes **relaxation** of the detrusor ($\beta_2/\beta_3$) and **contraction** of the internal sphincter ($\alpha_1$) to promote urinary retention. * **C. Bronchial smooth muscle contraction:** This is a **parasympathetic** effect ($M_3$). Sympathetic stimulation causes **bronchodilation** via **$\beta_2$ receptors** to increase airflow for oxygenation. ### **High-Yield NEET-PG Pearls** * **Dual Supply Exception:** Most blood vessels only have sympathetic innervation. Vasoconstriction is $\alpha_1$ mediated, while vasodilation in skeletal muscle is $\beta_2$ mediated. * **Sweat Glands:** Anatomically sympathetic but **cholinergic** (mediated by Acetylcholine acting on $M$ receptors). * **Mnemonic for SNS:** "Dilation" (Pupils, Bronchioles) and "Constriction" (Sphincters, Peripheral Vessels).

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

Stewart-Hamilton principle. ### 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.

Q: When capillary hydrostatic pressure is 30 mm of Hg and interstitial hydrostatic pressure is 5 mm of Hg, and the colloid oncotic pressure of capillaries is 25 mm of Hg and the interstitium is 5 mm of Hg, what is the net filtration pressure?

5 mm Hg. ### Explanation The net movement of fluid across a capillary membrane is determined by **Starling’s Forces**. The Net Filtration Pressure (NFP) is calculated using the Starling equation: **NFP = (Forces favoring filtration) – (Forces opposing filtration)** **NFP = [ (Pc + πi) – (Pi + πc) ]** Where: * **Pc** (Capillary Hydrostatic Pressure) = 30 mm Hg (Favors filtration) * **πi** (Interstitial Oncotic Pressure) = 5 mm Hg (Favors filtration) * **Pi** (Interstitial Hydrostatic Pressure) = 5 mm Hg (Opposes filtration) * **πc** (Capillary Oncotic Pressure) = 25 mm Hg (Opposes filtration) **Calculation:** NFP = (30 + 5) – (5 + 25) NFP = 35 – 30 = **5 mm Hg** Since the result is positive, there is a net movement of fluid out of the capillary into the interstitial space. #### Analysis of Incorrect Options: * **B (10 mm Hg):** This error usually occurs if one forgets to subtract the interstitial hydrostatic pressure or incorrectly adds the oncotic pressures. * **C (15 mm Hg):** This result occurs if the interstitial oncotic pressure is ignored or if the hydrostatic pressures are subtracted incorrectly (30 - 15). * **D (20 mm Hg):** This value is obtained if only the difference between the two hydrostatic pressures (30 - 10) or two oncotic pressures is considered in isolation. #### High-Yield Clinical Pearls for NEET-PG: 1. **Edema Formation:** Edema occurs when NFP increases significantly, often due to increased $P_c$ (e.g., Heart Failure), decreased $\pi_c$ (e.g., Nephrotic Syndrome, Cirrhosis), or lymphatic obstruction. 2. **The "Safety Factor":** The lymphatic system can increase its flow up to 20-fold to compensate for increased filtration before clinical edema becomes apparent. 3. **Negative Interstitial Pressure:** In most loose subcutaneous tissues, the interstitial hydrostatic pressure ($P_i$) is actually slightly **sub-atmospheric (negative)**, which helps hold the tissues together.

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.

Question 1

In a patient with a transplanted heart, which of the following mechanisms contributes to the increase in cardiac output during exercise?

Accepted Answer

Circulating epinephrine released from the adrenal medulla

Answer

Reinnervation of the transplanted heart by the vagus nerve

Answer

Intrinsic contractile mechanisms of the transplanted heart

Answer

The Bainbridge reflex

Question 2

Cardiac output depends on all of the following except?

Accepted Answer

Body surface area

Answer

Cardiac rate

Answer

Stroke volume

Answer

Cardiac contractility

Question 3

What is the main role of angiotensin II?

Accepted Answer

Increased TPR

Answer

Constriction of afferent renal arteriole

Answer

Decreased release of aldosterone

Answer

Diuresis

Question 4

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

Accepted Answer

End-diastolic volume

Answer

Increase in heart rate

Answer

End-systolic volume

Answer

Ejection systolic volume

Question 5

Endothelium-derived relaxing factor is:

Accepted Answer

Nitric oxide

Answer

Angiotensin

Answer

Serotonin

Answer

Norepinephrine

Question 6

What is the effect of sympathetic stimulation?

Accepted Answer

Vasoconstriction of skin and mucus membranes

Answer

Pupillary constriction

Answer

Contraction of bladder detrusor

Answer

Bronchial smooth muscle contraction

Question 7

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

Accepted Answer

Stewart-Hamilton principle

Answer

Hagen-Poiseuille principle

Answer

Bernoulli's principle

Answer

Universal gas equation

Question 8

When capillary hydrostatic pressure is 30 mm of Hg and interstitial hydrostatic pressure is 5 mm of Hg, and the colloid oncotic pressure of capillaries is 25 mm of Hg and the interstitium is 5 mm of Hg, what is the net filtration pressure?

Accepted Answer

5 mm Hg

Answer

10 mm Hg

Answer

15 mm Hg

Answer

20 mm Hg

Question 9

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 10

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-)

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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