Cardiovascular System Practice Questions

Q: Acetylcholine decreases heart rate by:

Acting on specific K+ channels and increasing efflux. **Explanation:** The heart rate is primarily regulated by the autonomic nervous system’s effect on the **Sinoatrial (SA) node**. Acetylcholine (ACh) is the primary neurotransmitter of the parasympathetic system (vagus nerve). **1. Why Option A is Correct:** ACh binds to **Muscarinic (M2) receptors** in the SA node. This leads to the activation of a specific type of G-protein-coupled inward-rectifier potassium channel known as **$K_{ACh}$ channels**. Activation of these channels causes an **increased efflux (outward movement) of $K^+$ ions**. This loss of positive charge results in **hyperpolarization** of the nodal cells, making the resting membrane potential more negative. Consequently, it takes longer for the prepotential to reach the threshold, thereby decreasing the heart rate (negative chronotropic effect). **2. Why Other Options are Incorrect:** * **Option B:** $Ca^{2+}$ ions are in higher concentration extracellularly; therefore, they do not "efflux" to decrease heart rate. Furthermore, ACh actually *decreases* $Ca^{2+}$ conductance. * **Option C:** $K^+$ ions move out of the cell (efflux) down their concentration gradient, not into the cell (influx). * **Option D:** Increasing $Ca^{2+}$ influx would cause depolarization and increase the heart rate (the mechanism of Sympathetic/Catecholamine action). ACh inhibits $I_{Ca}$ (calcium current) and $I_f$ (funny current). **Clinical Pearls for NEET-PG:** * **Vagal Tone:** The resting heart rate is lower than the intrinsic SA node rate (100 bpm) due to continuous vagal "tone" mediated by ACh. * **Atropine:** A competitive antagonist of M2 receptors; it blocks ACh action, leading to tachycardia. It is the drug of choice for symptomatic bradycardia. * **Mechanism Summary:** ACh $\rightarrow$ M2 Receptor $\rightarrow$ $\uparrow$ $K^+$ conductance + $\downarrow$ cAMP $\rightarrow$ Hyperpolarization $\rightarrow$ $\downarrow$ Heart Rate.

Q: Which of the following is the last part of the ventricle to be depolarized?

Epicardium of the base of the left ventricle. ### Explanation The sequence of ventricular depolarization is a high-yield concept in cardiac physiology, determined by the specialized conduction system (Purkinje fibers). **1. Why Option A is Correct:** Ventricular depolarization follows a specific anatomical sequence: * **Direction 1 (Septum to Apex):** It begins at the left side of the interventricular septum and moves toward the apex. * **Direction 2 (Endocardium to Epicardium):** Because Purkinje fibers are located in the subendocardial layer, the electrical impulse travels from the **inner (endocardial) surface to the outer (epicardial) surface.** * **Direction 3 (Apex to Base):** The wave of depolarization sweeps from the apex toward the base of the heart. Consequently, the **posterobasal portion of the left ventricle** (specifically the epicardial surface) is the furthest point from the initial septal activation and the last to receive the impulse. **2. Why Other Options are Incorrect:** * **B & D (Endocardium):** The endocardium is always depolarized *before* the epicardium because the Purkinje system initiates the impulse from the subendocardial layer. * **C & D (Apical regions):** The apex is one of the earliest regions to depolarize as the Bundle of His branches reach the papillary muscles and apical walls first. **3. NEET-PG High-Yield Pearls:** * **First part to depolarize:** Left side of the interventricular septum (moving left to right). * **First part to repolarize:** Epicardium (Repolarization occurs in the *opposite* direction of depolarization: Epicardium $\rightarrow$ Endocardium). * **Septal Q-wave:** Initial septal depolarization (left to right) is responsible for the small physiological Q-waves seen in lateral leads (V5, V6). * **Total Ventricular Conduction Time:** Approximately 0.06 seconds.

Q: Increase in heart rate just before starting exercise is due to?

Release of adrenaline. **Explanation:** The increase in heart rate just before the commencement of exercise is known as the **Anticipatory Rise**. This phenomenon is primarily mediated by the **limbic system** and the **cerebral cortex**, which trigger the sympathetic nervous system and the adrenal medulla. **Why "Release of Adrenaline" is correct:** Before physical exertion begins, psychological anticipation triggers a sympathetic "fight-or-flight" response. This leads to the release of **epinephrine (adrenaline)** from the adrenal medulla and norepinephrine from sympathetic nerve endings. Adrenaline acts on the **$\beta_1$ receptors** of the SA node, increasing the rate of depolarization and resulting in tachycardia even before any muscle movement occurs. **Why other options are incorrect:** * **Proprioceptors (Option B):** These are mechanoreceptors located in joints and muscles. They stimulate the cardiorespiratory centers only **at the onset** of movement. While they contribute to the rapid rise in heart rate during the initial seconds of exercise, they do not account for the rise *before* exercise starts. * **Stretch Receptors (Option A):** Atrial stretch receptors (involved in the **Bainbridge reflex**) respond to increased venous return. During exercise, the skeletal muscle pump increases venous return, which then increases heart rate. However, this occurs **during** exercise, not before. **High-Yield Facts for NEET-PG:** * **Bainbridge Reflex:** Increased right atrial pressure $\rightarrow$ Increased heart rate (to prevent pooling of blood in veins). * **Marey’s Law:** Heart rate is inversely proportional to blood pressure (mediated by baroreceptors). * **Vagal Tone:** The resting heart rate is lower than the intrinsic SA node rate (100 bpm) due to dominant parasympathetic (vagal) tone. * **Anticipatory Response:** Also involves an increase in rate and depth of ventilation (hyperpnea) before exercise.

Q: A 60-year-old patient with a 25-year history of hypertension underwent renal artery Doppler, which showed narrowing and turbulence in the right renal artery. If the diameter of the lumen is reduced by 50%, by how much will the blood flow be reduced?

1/16th. ### Explanation The correct answer is **1/16th**. #### 1. Underlying Medical Concept: Poiseuille’s Law The relationship between blood vessel dimensions and blood flow is governed by **Poiseuille’s Law**. According to this principle, the flow rate ($Q$) is directly proportional to the fourth power of the radius ($r^4$) of the vessel: $$Q \propto r^4$$ In this scenario, the diameter (and thus the radius) is reduced by 50%, meaning the new radius is **1/2** of the original. To find the change in flow, we apply the fourth-power rule: $$(1/2)^4 = 1/2 \times 1/2 \times 1/2 \times 1/2 = \mathbf{1/16}$$ Therefore, reducing the lumen diameter by half results in the blood flow decreasing to **1/16th** of its original value. #### 2. Analysis of Incorrect Options * **A. 1/4th:** This would be the reduction if flow were proportional to the square of the radius ($r^2$), which applies to surface area, not flow. * **B. 1/8th:** This would be the reduction if flow were proportional to the cube of the radius ($r^3$). * **D. 1/32nd:** This would be the reduction if flow were proportional to the fifth power ($r^5$). #### 3. Clinical Pearls & High-Yield Facts for NEET-PG * **Resistance ($R$):** Resistance is inversely proportional to the fourth power of the radius ($R \propto 1/r^4$). If the radius is halved, resistance increases **16-fold**. * **Arterioles:** These are the primary "resistance vessels" of the body because small changes in their diameter (via sympathetic tone) lead to massive changes in total peripheral resistance (TPR) and blood pressure. * **Turbulence:** The question mentions turbulence, which occurs when the **Reynolds number** exceeds 2000. Narrowing (stenosis) increases velocity, which promotes turbulent flow, clinically heard as a **bruit** (e.g., renal artery bruit in hypertension).

Q: Peripheral resistance is maximum in which of the following?

Arteriole. ### Explanation The correct answer is **Arteriole**. **1. Why Arterioles have the maximum resistance:** According to **Poiseuille’s Law**, resistance ($R$) is inversely proportional to the fourth power of the radius ($r^4$). While capillaries have a smaller individual radius, **arterioles** are considered the primary "resistance vessels" of the systemic circulation for two reasons: * **Muscular Wall:** Arterioles possess a thick layer of smooth muscle in their tunica media, allowing them to constrict or dilate significantly under sympathetic and local metabolic control. * **Pressure Drop:** The greatest drop in mean arterial pressure (MAP) occurs as blood passes through the arterioles (from ~90 mmHg to ~35 mmHg). This steep pressure gradient is the physiological hallmark of high resistance. **2. Why other options are incorrect:** * **Aorta:** As the largest vessel, it has a massive radius. Since resistance is inversely proportional to radius, the aorta offers minimal resistance to flow. * **Artery:** Large and medium-sized arteries act as conduits. While they have some resistance, it is significantly lower than that of the terminal arterioles. * **Vein:** Veins are "capacitance vessels." They are highly distensible, have large lumens, and operate under low pressure, offering very low resistance. **3. NEET-PG High-Yield Pearls:** * **Total Peripheral Resistance (TPR):** Arterioles contribute approximately 50-70% of the total TPR. * **Capillaries vs. Arterioles:** Although an individual capillary is narrower than an arteriole, the **total cross-sectional area** of the capillary bed is much larger. This results in a lower resistance and the slowest velocity of blood flow (ideal for nutrient exchange). * **Sympathetic Control:** Arterioles are the main site of action for norepinephrine on $\alpha_1$ receptors to regulate systemic blood pressure.

Q: A patient suffers a severe hemorrhage resulting in a lowered mean arterial pressure. Which of the following would be elevated above normal levels?

Heart rate. **Explanation:** The physiological response to hemorrhage is driven by the **Baroreceptor Reflex**, which aims to restore mean arterial pressure (MAP) and maintain perfusion to vital organs. **Why Heart Rate is Elevated:** When hemorrhage occurs, the decrease in blood volume leads to a drop in venous return and cardiac output, causing a fall in MAP. This decrease in pressure is sensed by high-pressure baroreceptors (located in the carotid sinus and aortic arch). The reduced stretch on these receptors decreases their firing rate to the medulla, leading to: 1. **Increased Sympathetic outflow:** Stimulates the SA node to increase **Heart Rate** (tachycardia) and increases myocardial contractility. 2. **Decreased Parasympathetic (Vagal) tone:** Further contributes to the rise in heart rate. **Analysis of Incorrect Options:** * **A. Splanchnic blood flow:** This **decreases**. Sympathetic activation causes vasoconstriction of peripheral and visceral (splanchnic) beds to divert blood toward the brain and heart. * **B. Cardiopulmonary receptor activity:** These are "low-pressure" receptors in the atria and pulmonary vessels. In hemorrhage, decreased blood volume reduces the stretch on these receptors, thereby **decreasing** their firing rate. * **C. Right ventricular end-diastolic volume (RVEDV):** This **decreases**. Hemorrhage reduces total blood volume and venous return (preload), leading to lower filling volumes in the ventricles. **High-Yield Clinical Pearls for NEET-PG:** * **Tachycardia** is often the earliest clinical sign of compensatory shock. * **The Bainbridge Reflex** (which increases HR due to increased atrial stretch) is the *opposite* of what happens here; in hemorrhage, the Baroreceptor reflex dominates. * **Formula to remember:** $MAP = CO \times TPR$. To compensate for low $CO$ (due to low stroke volume), the body must increase $HR$ and $TPR$ (Total Peripheral Resistance).

Q: What is the most potent vasopressor?

Angiotensin II. **Explanation:** **Angiotensin II** is the correct answer because it is one of the most powerful endogenous vasoconstrictors known. It acts directly on **AT1 receptors** located on vascular smooth muscle cells, leading to intense systemic vasoconstriction. This increases total peripheral resistance (TPR) and, consequently, arterial blood pressure. It is significantly more potent than norepinephrine in its pressor effects. **Analysis of Incorrect Options:** * **Renin (B):** Renin is a proteolytic enzyme secreted by the juxtaglomerular cells. It does not have any direct vasopressor activity; its role is to catalyze the conversion of Angiotensinogen to Angiotensin I. * **Aldosterone (C):** This is a mineralocorticoid that regulates blood pressure primarily through **volume expansion**. It promotes sodium and water reabsorption in the distal tubules, but it does not cause acute vasoconstriction. * **Cortisol (D):** While cortisol is essential for maintaining vascular tone by increasing the sensitivity of receptors to catecholamines (permissive effect), it is not a direct potent vasopressor. **High-Yield NEET-PG Pearls:** * **Potency Hierarchy:** While Angiotensin II is the most potent *physiological* vasopressor in this list, **Urotensin II** is technically the most potent endogenous vasoconstrictor discovered in humans (though rarely tested). * **RAAS Pathway:** Angiotensin I is converted to Angiotensin II by **ACE** (Angiotensin Converting Enzyme), primarily in the pulmonary capillaries. * **Clinical Link:** ACE inhibitors and ARBs (Angiotensin Receptor Blockers) are first-line antihypertensives because they block the potent pressor effects of Angiotensin II.

Question 1

In a standard Electrocardiogram, an augmented limb lead measures the electrical potential difference between which points?

Accepted Answer

One limb and two other limbs

Answer

Two limbs

Answer

One limb and a neutral (zero) reference

Answer

Two limbs and two other limbs

Question 2

Acetylcholine decreases heart rate by:

Accepted Answer

Acting on specific K+ channels and increasing efflux

Answer

Acting on Ca2+ channels and increasing efflux

Answer

Acting on specific K+ channels and increasing influx

Answer

Acting on specific Ca2+ channels and increasing influx

Question 3

Which of the following is the last part of the ventricle to be depolarized?

Accepted Answer

Epicardium of the base of the left ventricle

Answer

Endocardium of the base of the left ventricle

Answer

Apical epicardium

Answer

Apical endocardium

Question 4

Increase in heart rate just before starting exercise is due to?

Accepted Answer

Release of adrenaline

Answer

Stretch receptors

Answer

Proprioceptors

Answer

All of the above

Question 5

Massage of the carotid sinus results in all of the following, EXCEPT:

Accepted Answer

Decreased firing rate of the carotid sinus fibers

Answer

Increased pressure at the carotid sinus baroreceptors

Answer

Decreased firing rate of cardiac sympathetic fibers

Answer

Increased firing rate of the vagus nerve

Question 6

A 60-year-old patient with a 25-year history of hypertension underwent renal artery Doppler, which showed narrowing and turbulence in the right renal artery. If the diameter of the lumen is reduced by 50%, by how much will the blood flow be reduced?

Accepted Answer

1/16th

Answer

1/4th

Answer

1/8th

Answer

1/32nd

Question 7

Peripheral resistance is maximum in which of the following?

Accepted Answer

Arteriole

Answer

Aorta

Answer

Artery

Answer

Vein

Question 8

A patient has an aerial blood pressure of 90 mm Hg and a cardiac output of 5.4 L/min. What is the peripheral resistance?

Accepted Answer

1 R

Answer

2 R

Answer

4 R

Answer

6 R

Question 9

A patient suffers a severe hemorrhage resulting in a lowered mean arterial pressure. Which of the following would be elevated above normal levels?

Accepted Answer

Heart rate

Answer

Splanchnic blood flow

Answer

Cardiopulmonary receptor activity

Answer

Right ventricular end-diastolic volume

Question 10

What is the most potent vasopressor?

Accepted Answer

Angiotensin II

Answer

Renin

Answer

Aldosterone

Answer

Cortisol

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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