Cardiovascular System Practice Questions

Q: Which of the following is true about stroke volume?

It decreases with an increase in heart rate.. ### Explanation **Correct Option: A (It decreases with an increase in heart rate)** Stroke volume (SV) is the volume of blood pumped by the left ventricle per beat ($SV = EDV - ESV$). When the heart rate increases significantly (tachycardia), the duration of the cardiac cycle decreases. This reduction primarily affects **diastole**, the period when the ventricles fill with blood. Shorter diastolic filling time leads to a decreased **End-Diastolic Volume (EDV)**. According to the Frank-Starling Law, a lower EDV results in a reduced stroke volume. **Analysis of Incorrect Options:** * **B. It is determined by pre-diastolic volume:** This is a distractor term. SV is determined by **End-Diastolic Volume (EDV)** (preload), not "pre-diastolic" volume. * **C. It is determined by afterload:** While afterload *influences* SV (increased afterload decreases SV), the question asks for a "true statement" among the choices. Option A is a more fundamental physiological relationship in the context of the cardiac cycle. Furthermore, SV is determined by three factors: Preload, Afterload, and Contractility. * **D. It is equal to cardiac output:** This is mathematically incorrect. **Cardiac Output (CO) = Stroke Volume × Heart Rate**. SV is only one component of the total output per minute. **High-Yield Clinical Pearls for NEET-PG:** * **Frank-Starling Law:** Within physiological limits, the force of ventricular contraction is proportional to the initial length of the muscle fibers (EDV). * **Filling Time:** At heart rates above 170–180 bpm, SV drops so significantly that Cardiac Output may actually begin to fall despite the high rate. * **Ejection Fraction (EF):** $EF = (SV / EDV) \times 100$. Normal range is 55–70%. It is the most common clinical index of left ventricular function.

Q: Where is the major amount of angiotensin I converted to angiotensin II?

Lung. **Explanation:** The conversion of Angiotensin I to Angiotensin II is a critical step in the **Renin-Angiotensin-Aldosterone System (RAAS)**. This process is mediated by the **Angiotensin-Converting Enzyme (ACE)**. 1. **Why Lung is Correct:** While ACE is present in various vascular beds (including the kidneys and heart), the **lungs** contain the highest concentration of this enzyme. The pulmonary circulation receives the entire cardiac output, and the extensive surface area of the pulmonary capillary endothelium provides a massive site for ACE activity. Consequently, the majority of systemic Angiotensin I is converted to Angiotensin II during its first pass through the pulmonary vasculature. 2. **Why Other Options are Incorrect:** * **Liver:** The liver is the site of synthesis for **Angiotensinogen** (the precursor protein), but it is not the primary site for the conversion of Angiotensin I to II. * **Kidney:** The kidneys (specifically the Juxtaglomerular apparatus) secrete **Renin**, which converts Angiotensinogen to Angiotensin I. While some local conversion to Angiotensin II occurs in the renal endothelium, it is not the "major" site compared to the lungs. **High-Yield Clinical Pearls for NEET-PG:** * **ACE Inhibitors (e.g., Enalapril):** These drugs block the conversion in the lungs, leading to decreased blood pressure. A common side effect is a **dry cough**, caused by the accumulation of **Bradykinin** (which ACE normally degrades). * **Angiotensin II Functions:** It is a potent vasoconstrictor, stimulates Aldosterone secretion from the adrenal cortex, and triggers thirst/ADH release. * **Alternative Pathway:** Small amounts of Angiotensin II can be produced via non-ACE pathways involving enzymes like **Chymase**.

Q: Which of the following are known as the resistance vessels?

Arterioles. **Explanation:** **Arterioles** are designated as the **resistance vessels** of the cardiovascular system because they offer the highest resistance to blood flow. According to **Poiseuille’s Law**, resistance is inversely proportional to the fourth power of the radius ($R \propto 1/r^4$). Arterioles have a small lumen and a thick layer of smooth muscle in their walls, allowing them to undergo significant changes in diameter (vasoconstriction and vasodilation) under the influence of the sympathetic nervous system and local metabolites. This makes them the primary site for regulating **Total Peripheral Resistance (TPR)** and systemic arterial blood pressure. **Why other options are incorrect:** * **Venules:** Known as **capacitance vessels** (along with veins), they hold approximately 60-70% of the total blood volume due to their high distensibility. * **Capillaries:** Known as **exchange vessels**. Although they have the smallest individual radius, their massive total cross-sectional area results in the slowest blood flow velocity, facilitating nutrient and gas exchange. * **Aorta:** Known as a **distributing/windkessel vessel**. Its high elastic content allows it to dampen the pulsatile output of the heart, maintaining continuous flow during diastole. **High-Yield Clinical Pearls for NEET-PG:** * **Site of maximum pressure drop:** The largest drop in mean arterial pressure occurs across the arterioles (from ~90 mmHg to ~35 mmHg). * **Velocity vs. Area:** Blood flow velocity is lowest in capillaries (highest area) and highest in the aorta (lowest area). * **Critical Closing Pressure:** The internal pressure at which a small vessel (arteriole) collapses and flow ceases.

Q: Velocity of blood flow is inversely proportional to which of the following?

Square of the radius. **Explanation:** The velocity of blood flow ($v$) is governed by the relationship between the flow rate ($Q$) and the total cross-sectional area ($A$) of the vascular bed, expressed by the formula: **$v = Q / A$** Since blood vessels are cylindrical, the cross-sectional area ($A$) is calculated as **$\pi r^2$**. Substituting this into the equation gives: **$v = Q / \pi r^2$** This demonstrates that velocity is **inversely proportional to the square of the radius ($1/r^2$)**. As the total cross-sectional area increases (as seen in the transition from the aorta to the vast network of capillaries), the velocity of blood flow significantly decreases, allowing adequate time for nutrient exchange. **Analysis of Incorrect Options:** * **B. Compliance:** Compliance refers to the distensibility of a vessel ($\Delta V / \Delta P$). While it affects pulse pressure and blood storage, it does not have a direct inverse mathematical relationship with velocity. * **C & D. Cardiac Output / Stroke Volume:** These represent the flow rate ($Q$). According to the formula $v = Q/A$, velocity is **directly proportional** to flow. Therefore, an increase in cardiac output or stroke volume would increase the velocity of flow, not decrease it. **High-Yield Clinical Pearls for NEET-PG:** * **Capillaries** have the **largest total cross-sectional area** and, therefore, the **lowest velocity** of blood flow (approx. 0.03 cm/sec). * The **Aorta** has the **smallest total cross-sectional area** and the **highest velocity** (approx. 40 cm/sec). * **Bernoulli’s Principle:** In a narrowed vessel (decreased radius), velocity increases, which leads to a decrease in lateral pressure. This is relevant in understanding vascular bruits and murmurs.

Q: The pre-depolarization phase of the SA node Action potential is due to?

Ca++ entry. ### Explanation The SA node acts as the primary pacemaker of the heart because it exhibits **automaticity**, characterized by a slow, spontaneous depolarization known as the **pacemaker potential** (Phase 4). **Why Option B is Correct:** The pre-depolarization (pacemaker potential) occurs in two stages. While the initial phase is triggered by the "funny" sodium current ($I_f$), the **late stage of pre-depolarization** is specifically driven by the opening of **T-type (Transient) Calcium channels**. These channels allow $Ca^{2+}$ entry, pushing the membrane potential toward the threshold. Once the threshold is reached, **L-type (Long-lasting) Calcium channels** open, causing the actual depolarization (Phase 0). Therefore, $Ca^{2+}$ entry is the critical ion movement leading up to the action potential. **Why Other Options are Incorrect:** * **Option A:** $K^+$ entry would cause hyperpolarization, not depolarization. In the SA node, $K^+$ **efflux** is responsible for repolarization (Phase 3). * **Option C:** While $Na^+$ entry via $I_f$ channels starts the pacemaker potential, the question specifically targets the phase leading into the upstroke. In many competitive exams, the influx of Calcium is highlighted as the definitive trigger for reaching the threshold in nodal tissue. * **Option D:** $Cl^-$ efflux is not a significant contributor to the pacemaker potential in cardiac physiology. ### High-Yield Clinical Pearls for NEET-PG: * **Phase 0 in SA Node:** Driven by $Ca^{2+}$ influx (unlike ventricular muscle, which uses $Na^+$). * **Funny Current ($I_f$):** Activated by hyperpolarization; it is the target of the drug **Ivabradine**, used in chronic heart failure to reduce heart rate. * **Autonomic Control:** Acetylcholine increases $K^+$ conductance (hyperpolarization), slowing the heart rate, while Norepinephrine increases $Ca^{2+}$ and $I_f$ conductance, increasing the heart rate.

Q: Which type of blood vessel primarily regulates blood flow into capillary beds?

Arterioles. **Explanation:** **Why Arterioles are the Correct Answer:** Arterioles are known as the **"resistance vessels"** of the circulatory system. They possess a thick layer of smooth muscle in their walls relative to their lumen size, which is richly innervated by sympathetic adrenergic fibers. By undergoing vasoconstriction or vasodilation, arterioles create the greatest proportion of **Total Peripheral Resistance (TPR)**. This allows them to act as "adjustable nozzles," precisely regulating the volume and pressure of blood entering the fragile capillary beds. According to **Poiseuille’s Law**, since resistance is inversely proportional to the fourth power of the radius ($R \propto 1/r^4$), even small changes in arteriolar diameter significantly impact blood flow. **Analysis of Incorrect Options:** * **Arteries:** These are "conduit vessels" designed to transport blood under high pressure. While they have elastic properties to dampen pulsatility (Windkessel effect), they are not the primary site of resistance. * **Venules:** These are "capacitance vessels" that collect blood from capillaries. Their primary role is returning blood to the heart and serving as a reservoir for blood volume. * **Capillaries:** These are "exchange vessels." They lack smooth muscle entirely, consisting only of a single layer of endothelial cells, making them incapable of active diameter regulation. **High-Yield Clinical Pearls for NEET-PG:** * **Site of Maximum Pressure Drop:** The largest drop in mean arterial pressure occurs across the arterioles. * **Pre-capillary Sphincters:** These are functional rings of smooth muscle at the arteriolar-capillary junction that determine the *number* of capillaries perfused at any given time. * **Pharmacology Link:** Drugs like Calcium Channel Blockers (e.g., Amlodipine) primarily act on arterioles to reduce TPR and blood pressure.

Q: What happens to the slope of the pacemaker potential when vagal tone is increased?

Decreased Na+ influx, decreased slope. ### Explanation **1. Underlying Medical Concept** The pacemaker potential (Phase 4) in the SA node is primarily driven by the **Funny current ($I_f$)**, which involves the slow influx of **Na+** through HCN channels. When **vagal tone** (parasympathetic activity) increases, Acetylcholine is released. It binds to **$M_2$ receptors** in the SA node, leading to: * **Decreased cAMP levels:** This reduces the opening of HCN channels, leading to **decreased Na+ influx**. * **Activation of $K_{ACh}$ channels:** This causes K+ efflux, hyperpolarizing the cell. * **Result:** The rate of spontaneous depolarization slows down, meaning the **slope of the pacemaker potential decreases**. This increases the time required to reach the threshold, thereby decreasing the heart rate (negative chronotropy). **2. Analysis of Incorrect Options** * **Option A & D:** Increased vagal tone *decreases* the heart rate. An "increased slope" would mean reaching the threshold faster, which increases heart rate (sympathetic effect). * **Option C:** While a decreased slope is correct for vagal stimulation, it is caused by *decreased* Na+ influx, not increased. Increased Na+ influx would steepen the slope. **3. Clinical Pearls & High-Yield Facts for NEET-PG** * **Sympathetic Stimulation:** Acts via $\beta_1$ receptors to increase cAMP, increasing $I_f$ (Na+ influx) and $I_{Ca}$ (Ca2+ influx), which **increases the slope**. * **Phase 0 in SA Node:** Unlike ventricular muscle (Na+ driven), the upstroke in pacemaker cells is due to **Ca2+ influx** (L-type channels). * **Resting Membrane Potential:** Pacemaker cells do not have a true "resting" potential; they have a "maximal diastolic potential" of approximately -60 mV. * **Vagal Escape:** If vagal stimulation is intense and prolonged, the ventricles may begin to beat at their own intrinsic rate (Purkinje fiber rhythm).

Question 1

Which of the following is true about stroke volume?

Accepted Answer

It decreases with an increase in heart rate.

Answer

It is determined by pre-diastolic volume.

Answer

It is determined by afterload.

Answer

It is equal to cardiac output.

Question 2

An increase in contractility is demonstrated on a Frank-Starling diagram by?

Accepted Answer

Increased cardiac output for a given end-diastolic volume

Answer

Increased cardiac output for a given end-systolic volume

Answer

Decreased cardiac output for a given end-diastolic volume

Answer

Decreased cardiac output for a given end-systolic volume

Question 3

Where is the major amount of angiotensin I converted to angiotensin II?

Accepted Answer

Lung

Answer

Liver

Answer

Kidney

Answer

None of the above

Question 4

Myocardial oxygen demand depends upon which of the following?

Accepted Answer

Afterload

Answer

Preload

Answer

Intramyocardial tension

Answer

Myocardial muscle mass

Question 5

Which of the following are known as the resistance vessels?

Accepted Answer

Arterioles

Answer

Venules

Answer

Capillaries

Answer

Aorta

Question 6

Velocity of blood flow is inversely proportional to which of the following?

Accepted Answer

Square of the radius

Answer

Compliance of the blood vessel

Answer

Cardiac output

Answer

Stroke volume

Question 7

The pre-depolarization phase of the SA node Action potential is due to?

Accepted Answer

Ca++ entry

Answer

K+ entry

Answer

Na+ entry towards the end of repolarization

Answer

Cl- efflux

Question 8

Which type of blood vessel primarily regulates blood flow into capillary beds?

Accepted Answer

Arterioles

Answer

Arteries

Answer

Venules

Answer

Capillaries

Question 9

Which of the following situations will lead to increased viscosity of blood?

Accepted Answer

Multiple myeloma

Answer

Fasting state

Answer

Hypoglycemia

Answer

Amyloidogenesis

Question 10

What happens to the slope of the pacemaker potential when vagal tone is increased?

Accepted Answer

Decreased Na+ influx, decreased slope

Answer

Increased Na+ influx, increased slope

Answer

Increased Na+ influx, decreased slope

Answer

Decreased Na+ influx, increased slope

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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