Cardiovascular System Practice Questions

Q: Discharge from baroreceptors causes inhibition of which of the following medullary centers?

Rostral ventrolateral medulla. ### Explanation The baroreceptor reflex is the body's primary mechanism for short-term blood pressure regulation. When blood pressure rises, baroreceptors (located in the carotid sinus and aortic arch) increase their firing rate. **Why Option B is Correct:** The **Rostral Ventrolateral Medulla (RVLM)** is the primary **vasoconstrictor center** (pressor area). It sends excitatory glutamatergic fibers to the sympathetic preganglionic neurons in the spinal cord. To lower blood pressure, the baroreceptor reflex must **inhibit** the RVLM. This inhibition results in decreased sympathetic outflow, leading to vasodilation and a drop in peripheral resistance. **Analysis of Incorrect Options:** * **C. Nucleus of Tractus Solitarius (NTS):** This is the first relay station. Baroreceptor afferents (via CN IX and X) **excite** the NTS. It does not get inhibited. * **A. Caudal Ventrolateral Medulla (CVLM):** When the NTS is excited, it activates the CVLM. The CVLM then releases GABA to inhibit the RVLM. Thus, the CVLM is **stimulated**, not inhibited. * **D. Nucleus Ambiguus:** This is the cardioinhibitory center (parasympathetic). The NTS **excites** the Nucleus Ambiguus to increase vagal tone, slowing the heart rate. **High-Yield NEET-PG Pearls:** 1. **The Pathway:** Baroreceptors → NTS (+) → CVLM (+) → RVLM (–) → Decreased Sympathetic Tone. 2. **Neurotransmitters:** The NTS uses **Glutamate** to excite the CVLM; the CVLM uses **GABA** to inhibit the RVLM. 3. **Location:** The RVLM is located in the medulla; its destruction leads to a massive drop in basal blood pressure. 4. **Carotid Sinus vs. Aortic Arch:** Carotid sinus baroreceptors (CN IX) are more sensitive to both increases and decreases in pressure, whereas aortic arch receptors (CN X) primarily respond to increases.

Q: Which endogenous peptide causes vasodilation and is inactivated by angiotensin-converting enzyme?

Bradykinin. **Explanation:** The correct answer is **Bradykinin**. **1. Why Bradykinin is correct:** Bradykinin is a potent endogenous vasodilator peptide belonging to the kinin system. It acts on $B_2$ receptors to release nitric oxide and prostacyclin. Crucially, **Angiotensin-Converting Enzyme (ACE)**, also known as **Kininase II**, is the primary enzyme responsible for the degradation (inactivation) of bradykinin. When ACE is inhibited (e.g., by Enalapril), bradykinin levels rise, leading to vasodilation but also common side effects like dry cough and angioedema. **2. Why the other options are incorrect:** * **Angiotensinogen:** This is an α-2-globulin produced by the liver. It is the precursor protein acted upon by *renin* to form Angiotensin-I, not a vasodilator. * **Angiotensin-I:** This is a decapeptide formed from angiotensinogen. It is biologically inactive and is **converted** (not inactivated) by ACE into the potent vasoconstrictor Angiotensin-II. * **Angiotensin-II:** This is the primary effector molecule of the RAAS system. It is a potent **vasoconstrictor** (not a vasodilator) and is produced by the action of ACE, not inactivated by it. **3. NEET-PG Clinical Pearls:** * **ACE Inhibitor-induced Cough:** The accumulation of bradykinin in the lungs is the classic cause of the dry, irritating cough seen in patients on ACE inhibitors. * **Dual Role of ACE:** Remember that ACE has two primary functions: converting Angiotensin-I to Angiotensin-II (vasoconstriction) and inactivating Bradykinin (preventing vasodilation). * **Icatibant:** A selective $B_2$ receptor antagonist used in the treatment of Hereditary Angioedema (where bradykinin levels are excessively high).

Q: In an ECG, what is the duration of one small division?

0.04 sec. **Explanation:** The standard ECG paper speed is **25 mm/sec**. This constant speed is the basis for calculating time intervals on the horizontal axis of an ECG tracing. 1. **Why 0.04 sec is correct:** The ECG grid consists of small squares (1 mm) and large squares (5 mm). * Since 25 mm = 1 second, then 1 mm = 1/25 second. * **1/25 second = 0.04 seconds.** Therefore, one small division (1 mm) represents 0.04 seconds. Consequently, one large box (5 small divisions) represents 0.20 seconds (0.04 × 5). 2. **Analysis of Incorrect Options:** * **0.4 sec:** This is ten times the duration of a small box. It represents two large boxes. * **0.02 sec:** This would be the duration only if the paper speed were doubled to 50 mm/sec (sometimes used in pediatrics to resolve fast heart rates). * **0.1 sec:** This represents 2.5 small divisions or half of a large box. **High-Yield Clinical Pearls for NEET-PG:** * **Standard Calibration:** On the vertical axis, 10 mm (2 large boxes) equals **1 mV**. * **Heart Rate Calculation:** * Rate = 300 / (number of large boxes between R-R intervals). * Rate = 1500 / (number of small boxes between R-R intervals). * **Paper Speed Variations:** If the paper speed is increased to 50 mm/sec, the waves appear wider, and the duration of a small box becomes 0.02 sec. * **Normal PR Interval:** 0.12 to 0.20 seconds (3 to 5 small boxes). * **Normal QRS Duration:** < 0.12 seconds (< 3 small boxes).

Q: Which of the following is NOT true about the SA node?

It is supplied by the left vagus nerve.. **Explanation:** The **Sinoatrial (SA) node** is the physiological pacemaker of the heart, located at the junction of the superior vena cava and the right atrium. **Why Option C is the correct (false) statement:** The SA node is predominantly supplied by the **right vagus nerve**, while the Atrioventricular (AV) node is supplied by the **left vagus nerve**. This anatomical distribution is clinically significant: stimulation of the right vagus primarily slows the heart rate (negative chronotropy) by affecting the SA node, whereas stimulation of the left vagus primarily slows conduction through the AV node (negative dromotropy). **Analysis of other options:** * **Option A:** The SA node is supplied by the **nodal artery**, which arises from the Right Coronary Artery (RCA) in approximately 60% of individuals and the Left Circumflex Artery (LCX) in 40%. * **Option B:** It is the **primary pacemaker** because it possesses the highest intrinsic rate of spontaneous depolarization (60–100 bpm) due to the presence of "funny" currents ($I_f$). * **Option D:** Histologically, the SA node consists of specialized **P-cells** (pacemaker cells), transitional cells, and a dense matrix of **connective tissue** which increases with age. **NEET-PG High-Yield Pearls:** * **Location:** Subepicardial, in the *sulcus terminalis*. * **Blood Supply:** Most common source is the **Right Coronary Artery**. * **Ion Channels:** The prepotential (phase 4) is due to $I_f$ (sodium) channels, $T$-type calcium channels, and decreasing potassium efflux. * **Vagal Escape:** If vagal stimulation is intense, the heart may stop and then resume beating at a slower rate (ventricular escape), usually driven by the Purkinje system.

Q: Cardiac output is determined by which of the following?

Mean stroke volume. ### Explanation **Correct Answer: B. Mean stroke volume** **The Concept:** Cardiac Output (CO) is defined as the volume of blood pumped by each ventricle per minute. It is mathematically expressed by the formula: **Cardiac Output (CO) = Stroke Volume (SV) × Heart Rate (HR)** Stroke volume is the amount of blood ejected by the left ventricle in one contraction. Since CO is directly proportional to stroke volume, the **mean stroke volume** is a primary determinant of the total output. If stroke volume increases (via Frank-Starling mechanism or increased contractility) while the heart rate remains stable, the cardiac output increases. **Analysis of Incorrect Options:** * **Option A (Ratio of organ to total peripheral resistance):** This determines the **distribution** of blood flow to specific organs, not the total volume pumped by the heart. * **Option C (Mean arterial blood pressure):** MAP is a *result* of cardiac output and systemic vascular resistance (MAP = CO × SVR + CVP). While high afterload (pressure) can oppose ejection, MAP itself is not a primary determinant of CO; rather, CO helps determine MAP. * **Option D (Contractility of the heart):** While contractility *influences* stroke volume (and thus CO), it is an intrinsic property. In the context of the standard physiological equation, stroke volume is the direct quantitative determinant. **High-Yield Clinical Pearls for NEET-PG:** * **Cardiac Index (CI):** It is CO adjusted for body surface area (Normal: 2.5–4.0 L/min/m²). It is a more accurate marker than CO. * **Fick’s Principle:** The gold standard for measuring CO. $CO = \frac{\text{Oxygen Consumption}}{\text{Arterial } O_2 \text{ content} - \text{Venous } O_2 \text{ content}}$. * **Preload vs. Afterload:** Increased preload (End-Diastolic Volume) increases SV (Frank-Starling Law), whereas increased afterload (SVR) typically decreases SV.

Q: During the Valsalva maneuver, how does the heart rate typically change?

Tachycardia followed by bradycardia. ### Explanation The **Valsalva maneuver** (forced expiration against a closed glottis) involves four distinct phases driven by changes in intrathoracic pressure and the baroreceptor reflex. **Why Option A is Correct:** The heart rate response is biphasic: 1. **Tachycardia (During the maneuver):** In **Phase II**, increased intrathoracic pressure decreases venous return (preload), leading to a drop in cardiac output and blood pressure. The **baroreceptor reflex** detects this hypotension and triggers sympathetic activation, resulting in compensatory **tachycardia**. 2. **Bradycardia (After the maneuver):** In **Phase IV** (Post-maneuver), the sudden release of pressure allows a massive surge of venous return to the heart. This causes an "overshoot" of arterial blood pressure. The baroreceptors respond to this hypertension by triggering the **parasympathetic nervous system (vagus nerve)**, resulting in reflex **bradycardia**. **Why Other Options are Incorrect:** * **Option B:** Reverses the physiological sequence; bradycardia occurs as a late reflex, not an initial response. * **Options C & D:** These options describe a sustained heart rate change. The maneuver is characterized by dynamic fluctuations (tachycardia during strain and bradycardia upon release) to maintain hemodynamic stability. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Use:** Used to terminate **Supraventricular Tachycardia (SVT)** by increasing vagal tone during Phase IV. * **Murmurs:** Valsalva **decreases** most murmurs (due to decreased venous return) but **increases** the intensity of murmurs in **Hypertrophic Obstructive Cardiomyopathy (HOCM)** and **Mitral Valve Prolapse (MVP)**. * **Square Wave Response:** In patients with Heart Failure, the normal BP fluctuations are lost, showing a "square wave" pattern due to fluid overload.

Q: Which structure is known as the gatekeeper of the heart?

AV node. **Explanation:** The **AV (Atrioventricular) node** is known as the **"Gatekeeper of the heart"** because it regulates the electrical impulses traveling from the atria to the ventricles. Its primary function is to provide a physiological delay (approx. 0.1 seconds), ensuring that the atria contract and empty their blood into the ventricles before ventricular contraction begins. Furthermore, in cases of atrial tachyarrhythmias (like atrial fibrillation), the AV node protects the ventricles by limiting the number of impulses that pass through, preventing a dangerously high ventricular rate. **Analysis of Options:** * **SA Node:** Known as the **"Pacemaker of the heart."** It initiates the impulse but does not act as a filter or gatekeeper. * **Purkinje Fibers:** These are responsible for the rapid conduction of impulses throughout the ventricular myocardium to ensure synchronous contraction. They have the fastest conduction velocity in the heart. * **Bundle of His:** This is the only electrical connection between the atria and ventricles, but it functions as a conduction pathway rather than a regulatory gate. **High-Yield Clinical Pearls for NEET-PG:** * **Slowest Conduction Velocity:** AV Node (0.01–0.05 m/s), which accounts for the AV nodal delay. * **Fastest Conduction Velocity:** Purkinje fibers (2–4 m/s). * **Blood Supply:** The AV node is supplied by the **Posterior Descending Artery (PDA)**. In 90% of individuals (right dominant), this arises from the Right Coronary Artery. * **Location:** The AV node is located in the **Koch’s Triangle** (bounded by the Tendon of Todaro, the septal leaflet of the tricuspid valve, and the coronary sinus orifice).

Q: Stroke volume can be decreased by which of the following?

Increasing heart rate. **Explanation:** Stroke Volume (SV) is the volume of blood pumped by the left ventricle per beat. It is determined by three primary factors: **Preload, Afterload, and Contractility.** **Why "Increasing Heart Rate" is correct:** When the heart rate increases significantly (tachycardia), the duration of the cardiac cycle decreases. This reduction occurs primarily at the expense of **diastole** (the filling phase). A shorter diastolic filling time leads to a decrease in **End-Diastolic Volume (EDV)**. According to the Frank-Starling Law, a lower EDV results in a reduced stroke volume. While cardiac output may initially stay stable due to the higher rate, the stroke volume itself decreases. **Analysis of Incorrect Options:** * **A. Increasing ventricular contractility:** This increases the force of contraction, leading to a lower End-Systolic Volume (ESV) and thus an **increase** in stroke volume. * **C. Decreasing total peripheral resistance (TPR):** TPR is a major component of afterload. Decreasing afterload makes it easier for the ventricle to eject blood, thereby **increasing** stroke volume. * **D. Decreasing systemic blood pressure:** Similar to option C, lower systemic pressure reduces the afterload against which the heart must pump, which typically **increases** stroke volume. **High-Yield NEET-PG Pearls:** * **Formula:** $Stroke Volume (SV) = EDV - ESV$. * **Frank-Starling Law:** Stroke volume increases in response to an increase in the volume of blood filling the heart (Preload), within physiological limits. * **Clinical Correlation:** In conditions like Supraventricular Tachycardia (SVT), the heart rate is so high that filling time is severely compromised, leading to a drop in SV and blood pressure (syncope). * **Inverse Relationship:** SV is directly proportional to Preload and Contractility, but inversely proportional to Afterload.

Question 1

Discharge from baroreceptors causes inhibition of which of the following medullary centers?

Accepted Answer

Rostral ventrolateral medulla

Answer

Caudal ventrolateral medulla

Answer

Nucleus of tractus solitarius

Answer

Nucleus ambiguus

Question 2

A 0.5 litre blood loss in 30 minutes will lead to which of the following physiological responses?

Accepted Answer

Slight increase in HR, normal BP

Answer

Increase in HR, decrease in BP

Answer

Decrease in HR and BP

Answer

Prominent increase in HR

Question 3

Which endogenous peptide causes vasodilation and is inactivated by angiotensin-converting enzyme?

Accepted Answer

Bradykinin

Answer

Angiotensinogen

Answer

Angiotensin–I

Answer

Angiotensin–II

Question 4

In an ECG, what is the duration of one small division?

Accepted Answer

0.04 sec

Answer

0.4 sec

Answer

0.02 sec

Answer

0.1 sec

Question 5

Which of the following is NOT true about the SA node?

Accepted Answer

It is supplied by the left vagus nerve.

Answer

It is supplied by the nodal artery.

Answer

It acts as the primary pacemaker of the heart.

Answer

It is composed of nodal cells and connective tissue.

Question 6

Cardiac output is determined by which of the following?

Accepted Answer

Mean stroke volume

Answer

Ratio of organ to total peripheral resistance

Answer

Mean arterial blood pressure

Answer

Contractility of the heart

Question 7

During the Valsalva maneuver, how does the heart rate typically change?

Accepted Answer

Tachycardia followed by bradycardia

Answer

Bradycardia followed by tachycardia

Answer

Tachycardia during and after the Valsalva maneuver

Answer

Bradycardia during and after the Valsalva maneuver

Question 8

During the T-P interval in an ECG of a patient with a damaged cardiac muscle, which of the following is true?

Accepted Answer

The entire ventricle is repolarized except for the damaged cardiac muscle

Answer

The entire ventricle is depolarized

Answer

The entire ventricle is depolarized except for the damaged cardiac muscle

Answer

The entire ventricle is repolarized

Question 9

Which structure is known as the gatekeeper of the heart?

Accepted Answer

AV node

Answer

SA node

Answer

Purkinje fibers

Answer

Bundle of His

Question 10

Stroke volume can be decreased by which of the following?

Accepted Answer

Increasing heart rate

Answer

Increasing ventricular contractility

Answer

Decreasing total peripheral resistance

Answer

Decreasing systemic blood pressure

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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