Cardiovascular System Practice Questions

Q: Coronary vasodilatation is caused by which of the following substances?

Adenosine. **Explanation:** **1. Why Adenosine is the Correct Answer:** Adenosine is the most potent local metabolic vasodilator of the coronary circulation. According to the **Metabolic Theory of Autoregulation**, when myocardial oxygen demand increases (e.g., during exercise), ATP is broken down into ADP, AMP, and eventually **Adenosine**. Adenosine diffuses out of the myocytes and binds to **A2A receptors** on the vascular smooth muscle of the coronary arterioles. This activates adenylate cyclase, increasing cAMP, which leads to smooth muscle relaxation and significant vasodilation. This mechanism ensures that coronary blood flow matches the metabolic needs of the heart. **2. Analysis of Incorrect Options:** * **Bradykinin & Histamine:** While both are potent vasodilators in the systemic circulation and play roles in inflammation and anaphylaxis, they are not the primary physiological regulators of coronary vascular tone. * **Ergotamine:** This is a vasoconstrictor (specifically an alpha-adrenergic agonist and 5-HT receptor agonist). It is used in treating migraines but is contraindicated in patients with coronary artery disease because it can induce **coronary vasospasm**. **3. NEET-PG High-Yield Clinical Pearls:** * **Coronary Steal Phenomenon:** Potent vasodilators like **Dipyridamole** and Adenosine can cause "steal" by dilating healthy vessels, diverting blood away from already maximally dilated stenotic vessels. * **Diagnostic Use:** Adenosine is the drug of choice (DOC) for the termination of **Paroxysmal Supraventricular Tachycardia (PSVT)** due to its ability to slow AV node conduction. * **Key Regulators:** While Adenosine is the primary metabolic regulator, **Nitric Oxide (NO)** is the primary endothelium-derived relaxant, and **Hypoxia** is the most potent direct stimulus for coronary vasodilation.

Q: When a person stands suddenly from a lying down posture, what physiological response occurs?

Increased tone of capacitance vessels.. When a person stands up suddenly, gravity causes approximately 500–1000 mL of blood to pool in the lower extremities. This leads to a transient decrease in venous return, stroke volume, and mean arterial pressure (MAP). **Explanation of the Correct Answer:** To counteract this drop in blood pressure, the **Baroreceptor Reflex** is activated. The decrease in MAP is sensed by baroreceptors in the carotid sinus and aortic arch, leading to a decrease in parasympathetic tone and an **increase in sympathetic outflow**. Sympathetic stimulation causes **venoconstriction** (increased tone of capacitance vessels). Since 60–70% of blood volume resides in the veins, this constriction shifts blood toward the heart, restoring venous return and cardiac output. **Analysis of Incorrect Options:** * **B. Increased efferent discharge from the IX cranial nerve:** The Glossopharyngeal nerve (IX) carries **afferent** (sensory) signals from the carotid sinus to the medulla. In response to hypotension, the *firing rate* of these afferent fibers actually **decreases**, not increases. * **C. Decreased heart rate:** Sympathetic activation leads to an **increase in heart rate** (tachycardia) and myocardial contractility to restore blood pressure. A decrease in heart rate would worsen the hypotension. **High-Yield Clinical Pearls for NEET-PG:** * **Orthostatic Hypotension:** Defined as a drop in systolic BP >20 mmHg or diastolic BP >10 mmHg within 3 minutes of standing. * **The "Buffer Nerve":** The Hering’s nerve (branch of CN IX) and Cyon’s nerve (branch of CN X) are known as buffer nerves because they help minimize fluctuations in BP. * **Initial Response:** The very first compensatory change is an increase in heart rate, followed by peripheral vasoconstriction.

Q: Cardiac index is determined by which of the following parameters?

Cardiac output and body surface area. **Explanation:** **1. Why the correct answer is right:** Cardiac Index (CI) is a hemodynamic parameter that relates the **Cardiac Output (CO)** to an individual's **Body Surface Area (BSA)**. Since people vary significantly in size, a standard cardiac output of 5 L/min might be adequate for a small person but insufficient for a large person. By dividing CO by BSA, we normalize the measurement to the individual's body size, providing a more accurate assessment of whether the heart is meeting the metabolic demands of the tissues. * **Formula:** $CI = \frac{Cardiac Output (CO)}{Body Surface Area (BSA)}$ * **Normal Range:** Approximately $2.5 \text{ to } 4.0 \text{ L/min/m}^2$. **2. Why the incorrect options are wrong:** * **Option B:** Stroke volume is only one component of cardiac output ($CO = SV \times HR$). Using stroke volume alone ignores the heart rate, which is essential for determining total flow. * **Option C:** Body surface area is the denominator, but it cannot determine the index without knowing the heart's actual output (the numerator). * **Option D:** Peripheral resistance (SVR) relates to blood pressure and afterload, not the normalization of flow relative to body size. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Clinical Significance:** A Cardiac Index below $2.2 \text{ L/min/m}^2$ is often used as a diagnostic threshold for **cardiogenic shock**. * **BSA Calculation:** Most commonly calculated using the **Mosteller formula** or DuBois formula. * **Age Factor:** Cardiac Index is highest at age 10 (approx. $4.5 \text{ L/min/m}^2$) and gradually declines with age. * **Key Distinction:** While Cardiac Output measures total flow, Cardiac Index measures **efficiency** relative to size.

Q: What is perfusion pressure?

Arterial–venous pressure difference. **Explanation:** **Perfusion pressure** is the pressure gradient that drives blood flow through an organ or a vascular bed. According to **Ohm’s Law** applied to hemodynamics ($Q = \Delta P / R$), the flow ($Q$) is directly proportional to the pressure difference ($\Delta P$) between two points. In the systemic circulation, blood flows from the high-pressure arterial system to the low-pressure venous system. Therefore, the perfusion pressure is defined as the **Arterial–Venous pressure difference** ($P_a - P_v$). * **Why Option C is correct:** For any organ, the net pressure available to push blood through the capillaries is the difference between the inflow (arterial) pressure and the outflow (venous) pressure. * **Why Option A & B are incorrect:** While arterial pressure is the primary driver, it does not account for the "back-pressure" exerted by the venous system. A single pressure point cannot define a gradient. * **Why Option D is incorrect:** Left ventricular pressure fluctuates significantly between systole and diastole and represents the pump's generation of pressure, not the specific gradient across a distal vascular bed. **High-Yield Clinical Pearls for NEET-PG:** 1. **Cerebral Perfusion Pressure (CPP):** A critical exam concept. $CPP = MAP - ICP$ (where MAP is Mean Arterial Pressure and ICP is Intracranial Pressure). If ICP rises, CPP falls, leading to ischemia. 2. **Renal Perfusion Pressure:** Primarily determined by MAP; the kidneys use autoregulation to maintain a constant GFR despite fluctuations in perfusion pressure (between 80–180 mmHg). 3. **Coronary Perfusion Pressure:** Unlike other organs, the left ventricle is perfused mainly during **diastole**. Its perfusion pressure is the difference between Aortic Diastolic Pressure and Left Ventricular End-Diastolic Pressure (LVEDP).

Q: Which part of the heart is the last to be repolarized?

Apical endocardium. **Explanation:** The sequence of cardiac electrical activity is a high-yield concept in physiology. To understand repolarization, one must first understand the sequence of depolarization. **1. Why Apical Endocardium is correct:** * **Depolarization** occurs from **Endocardium to Epicardium** and from **Apex to Base**. Therefore, the apical endocardium is the *first* part of the ventricles to depolarize. * **Repolarization**, however, occurs in the **reverse order** of depolarization. It proceeds from **Epicardium to Endocardium**. This is because the epicardial cells have a shorter action potential duration compared to endocardial cells (due to a higher density of $I_{to}$ potassium channels). * Additionally, repolarization moves from **Base to Apex**. * Since the apical endocardium is the first to depolarize and the last to finish its long action potential, it is the **last part of the heart to be repolarized**. **2. Analysis of Incorrect Options:** * **Apical epicardium:** This depolarizes early but repolarizes before the endocardium due to its shorter action potential duration. * **Epicardium of the base:** This is generally the **first** area to repolarize because repolarization begins at the epicardial surface of the base. * **Endocardium of the base:** While endocardial, the basal region repolarizes before the apical region. **Clinical Pearls for NEET-PG:** * **T-Wave Direction:** Because repolarization occurs in the opposite direction of depolarization (Epicardium $\rightarrow$ Endocardium), the T-wave remains **upright** (positive) in the same leads where the QRS complex is positive. * **Ischemia:** Subendocardial ischemia delays repolarization further, often leading to ST-segment depression or T-wave inversion. * **Sequence Summary:** * Depolarization: Endocardium $\rightarrow$ Epicardium; Apex $\rightarrow$ Base. * Repolarization: Epicardium $\rightarrow$ Endocardium; Base $\rightarrow$ Apex.

Q: The normal P wave is biphasic in which lead?

V1. **Explanation:** The **P wave** represents atrial depolarization. In a normal ECG, the P wave is typically **biphasic in Lead V1**. **Why V1 is correct:** Lead V1 is positioned horizontally over the 4th intercostal space, directly over the right atrium. Atrial depolarization occurs in two stages: 1. **Initial component:** Represents **Right Atrial (RA)** depolarization, moving anteriorly and toward V1 (causing a positive deflection). 2. **Terminal component:** Represents **Left Atrial (LA)** depolarization, moving posteriorly and away from V1 (causing a negative deflection). This dual directionality results in the characteristic "up-and-down" biphasic morphology in V1. **Why other options are incorrect:** * **Lead II (LII):** This is the best lead to visualize P waves. Since the vector of atrial depolarization moves inferiorly and toward the left (parallel to Lead II), the P wave is always **monophasic and positive**. * **aVF:** Similar to Lead II, this is an inferior lead. The depolarization vector moves toward it, resulting in a **positive** P wave. * **aVR:** The depolarization vector moves directly away from this lead (right shoulder). Therefore, the P wave in aVR is normally **inverted (negative)**, not biphasic. **High-Yield Clinical Pearls for NEET-PG:** * **P-mitrale:** A notched, wide P wave in Lead II (seen in Left Atrial Enlargement). * **P-pulmonale:** A tall, peaked P wave (>2.5 mm) in Lead II (seen in Right Atrial Enlargement). * **V1 Significance:** In Left Atrial Enlargement, the terminal negative component of the biphasic P wave in V1 becomes deeper (>1mm) and wider (>0.04s).

Q: In circulatory biomechanics, which of the following statements is true?

Cardiac output is increased in anemia.. ### Explanation **Correct Answer: C. Cardiac output is increased in anemia.** In **anemia**, the reduction in hemoglobin concentration leads to two primary physiological changes that increase cardiac output (CO): 1. **Reduced Viscosity:** A lower red blood cell count decreases blood viscosity. According to **Poiseuille’s Law**, decreased viscosity reduces peripheral resistance, facilitating easier blood flow and increasing venous return. 2. **Tissue Hypoxia:** Decreased oxygen-carrying capacity triggers peripheral vasodilation to improve oxygen delivery. This further reduces Total Peripheral Resistance (TPR). Since **CO = Mean Arterial Pressure / TPR**, a significant drop in TPR leads to a "hyperdynamic circulation" and increased cardiac output. **Analysis of Incorrect Options:** * **A & B (Viscosity):** Blood viscosity is primarily determined by the **hematocrit**. In **Anemia** (low RBCs), viscosity **decreases**. In **Polycythemia** (high RBCs), viscosity **increases**, which can lead to sluggish blood flow and increased risk of thrombosis. * **D (Beri-Beri):** Wet Beri-Beri (Thiamine/B1 deficiency) is a classic cause of **High-Output Heart Failure**. Thiamine deficiency leads to systemic vasodilation and impaired cellular metabolism, resulting in an **increased** cardiac output, not a decreased one. **High-Yield Clinical Pearls for NEET-PG:** * **High-Output States:** Remember the mnemonic **"ABCD"**: **A**nemia, **B**eri-Beri/AV malformations, **C**hronic Paget’s disease, and **D**eranged thyroid (Hyperthyroidism). * **Fahraeus-Lindqvist Effect:** In capillaries (vessels <300μm), blood viscosity decreases because RBCs move to the center of the vessel (axial streaming), leaving a plasma layer at the periphery. * **Viscosity & Velocity:** Viscosity is inversely proportional to the velocity of blood flow (non-Newtonian fluid behavior).

Question 1

Coronary vasodilatation is caused by which of the following substances?

Accepted Answer

Adenosine

Answer

Bradykinin

Answer

Histamines

Answer

Ergotamine

Question 2

When a person stands suddenly from a lying down posture, what physiological response occurs?

Accepted Answer

Increased tone of capacitance vessels.

Answer

Increased efferent discharge from the IX cranial nerve.

Answer

Decreased heart rate.

Answer

All of the above.

Question 3

In a study, dye ABC is used to measure cardiac output and blood volume. If the dye is replaced with a new dye XYZ which diffuses more rapidly out of the capillaries, how would this affect the study measurements?

Accepted Answer

Normal cardiac output, altered blood volume

Answer

Altered cardiac output, normal blood volume estimation

Answer

Both cardiac output and blood volume are altered

Answer

Both cardiac output and blood volume estimations are normal

Question 4

Which statement is true regarding blood pressure measurement using a sphygmomanometer compared to direct intra-arterial pressure measurements?

Accepted Answer

Sphygmomanometer measurements are more than intravascular pressure.

Answer

Sphygmomanometer measurements are less than intravascular pressure.

Answer

Sphygmomanometer measurements are equal to intravascular pressure.

Answer

The difference depends upon blood flow.

Question 5

What is common between systemic and pulmonary circulation?

Accepted Answer

Volume of the circulation per minute

Answer

Peripheral vascular resistance

Answer

Pulse pressure

Answer

Total vascular capacity

Question 6

Cardiac index is determined by which of the following parameters?

Accepted Answer

Cardiac output and body surface area

Answer

Stroke volume and body surface area

Answer

Body surface area only

Answer

Peripheral resistance

Question 7

What is perfusion pressure?

Accepted Answer

Arterial–venous pressure difference

Answer

Arterial pressure

Answer

Venous pressure

Answer

Pressure in the left ventricle

Question 8

Which part of the heart is the last to be repolarized?

Accepted Answer

Apical endocardium

Answer

Apical epicardium

Answer

Epicardium of the base of the left ventricle

Answer

Endocardium of the base of the left ventricle

Question 9

The normal P wave is biphasic in which lead?

Accepted Answer

V1

Answer

LII

Answer

aVF

Answer

aVR

Question 10

In circulatory biomechanics, which of the following statements is true?

Accepted Answer

Cardiac output is increased in anemia.

Answer

Blood viscosity is increased in anemia.

Answer

Blood viscosity is decreased in polycythemia.

Answer

Cardiac output is decreased in Beri-Beri.

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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