Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 861: Which of the following stimuli is primarily responsible for triggering the Bezold-Jarisch reflex?

A. Parasympathetic withdrawal
B. Decreased venous return
C. Increased sympathetic stimulation
D. Activation of cardiac C-fiber afferents (Correct Answer)

Explanation: ***Activation of cardiac C-fiber afferents*** - The **Bezold-Jarisch reflex** is primarily triggered by stimulation of **cardiac mechanoreceptors and chemoreceptors** located in the ventricles, particularly the inferoposterior wall of the left ventricle. - These receptors have **unmyelinated vagal C-fiber afferents** that transmit signals to the medullary cardiovascular centers. - Activation of these afferents leads to the characteristic triad: **bradycardia, hypotension, and vasodilation** via increased parasympathetic activity and withdrawal of sympathetic tone. - Common triggers include vigorous ventricular contraction with decreased filling, certain drugs (veratridine), myocardial ischemia (especially inferior wall MI), and reperfusion. *Decreased venous return* - While **decreased venous return** creates the hemodynamic context (ventricular underfilling) that can lead to vigorous contraction of a relatively empty ventricle, it is not itself the *trigger* of the reflex. - The actual trigger is the activation of the ventricular receptors sensing this abnormal contraction pattern, which then signal via C-fiber afferents. - Decreased venous return alone, without receptor activation, would not produce the reflex. *Parasympathetic withdrawal* - **Parasympathetic withdrawal** would cause tachycardia and is opposite to the Bezold-Jarisch reflex, which involves **increased parasympathetic activity**. - This is a compensatory response seen in other reflexes like the baroreceptor reflex during hypotension. *Increased sympathetic stimulation* - **Increased sympathetic stimulation** produces tachycardia, increased contractility, and vasoconstriction—effects opposite to the Bezold-Jarisch reflex. - The reflex actually causes **sympathetic withdrawal** along with parasympathetic activation.

Question 862: Which of the following is NOT an effect of Angiotensin II?

A. Stimulation of thirst
B. Aldosterone secretion
C. Increased ADH secretion
D. Vasodilation (Correct Answer)

Explanation: ***Vasodilation*** - **Angiotensin II** primarily causes **vasoconstriction** of arterioles, leading to an **increase in systemic vascular resistance** and blood pressure, rather than vasodilation. - This effect is crucial for maintaining blood pressure, especially in conditions of **hypovolemia** or **low renal perfusion**. *Stimulation of thirst* - **Angiotensin II** acts directly on the **hypothalamus** and subfornical organ to stimulate **thirst**, encouraging water intake to increase blood volume. - This helps to restore fluid balance and thereby **increase blood pressure**. *Aldosterone secretion* - **Angiotensin II** is a potent stimulator of **aldosterone secretion** from the adrenal cortex. - **Aldosterone** promotes **sodium and water reabsorption** in the kidneys, leading to increased blood volume and blood pressure. *Increased ADH secretion* - **Angiotensin II** stimulates the release of **antidiuretic hormone (ADH)**, also known as vasopressin, from the posterior pituitary gland. - **ADH** increases water reabsorption in the collecting ducts of the kidneys, contributing to higher blood volume and **blood pressure**.

Question 863: Slowest blood flow is seen in?

A. Arteriole
B. Veins
C. Capillaries (Correct Answer)
D. Venules

Explanation: ***Capillaries*** - Blood flow is slowest in capillaries due to their **large total cross-sectional area**, allowing sufficient time for efficient **exchange of nutrients, gases, and waste products** between blood and tissues. - Despite their individual small diameter, the combined area of millions of capillaries significantly reduces the overall velocity of blood flow. *Arteriole* - **Arterioles** are designed to **regulate blood flow** into capillary beds by constricting and dilating, but blood velocity is still relatively high compared to capillaries. - While smaller than arteries, the **cross-sectional area** of individual arterioles does not collectively exceed that of the major arteries enough to cause the slowest flow rate in the circulatory system. *Veins* - Blood flow in **veins** is generally faster than in capillaries, and is aided by muscle pumps and valves, as they collect blood from the capillary beds. - Although veins have a larger total capacity than arteries, the **velocity of blood flow increases** as blood returns to the heart through progressively larger vessels. *Venules* - **Venules** collect blood from capillaries and begin the return journey to the heart, with blood flow velocity starting to increase as they merge into larger veins. - While slightly faster than in capillaries, the flow in venules is still relatively slow compared to larger veins and arteries, but not the slowest in the system due to their **collecting function and relatively small combined cross-sectional area compared to the entire capillary network**.

Question 864: Deoxygenated blood is not seen in which of the following?

A. Pulmonary artery
B. Umbilical artery
C. Pulmonary vein (Correct Answer)
D. Right atrium

Explanation: ***Pulmonary vein*** - The pulmonary veins carry **oxygenated blood** from the lungs back to the left atrium of the heart. - Their primary function is to transport blood that has undergone **gas exchange** in the lungs, making it rich in oxygen. *Pulmonary artery* - The pulmonary artery carries **deoxygenated blood** from the right ventricle of the heart to the lungs. - This is an exception to the general rule that arteries carry oxygenated blood, as its purpose is to deliver blood for **oxygenation**. *Right atrium* - The right atrium receives **deoxygenated blood** from the systemic circulation via the superior and inferior vena cava. - It acts as a collecting chamber for blood that has supplied oxygen to the body's tissues before it is pumped to the lungs. *Umbilical artery* - The umbilical arteries carry **deoxygenated blood** and waste products from the fetus to the placenta. - In fetal circulation, these arteries are responsible for removing metabolic wastes and carbon dioxide from the fetal circulation.

Question 865: By what percentage can cardiac output increase in a healthy adult during intense physical activity compared to resting levels?

A. 300 - 400 % (Correct Answer)
B. 0 - 50 %
C. 50 - 100 %
D. 100 - 200 %

Explanation: ***300 - 400 %*** - In a healthy adult, **cardiac output** can increase remarkably during intense physical activity. - The heart can increase its output by **3 to 4 times** (or 300-400%) above resting levels during peak exertion. - At rest, cardiac output is approximately **5 L/min**, but during maximal exercise, it can reach **20-25 L/min** in well-conditioned individuals. - This represents the heart's **reserve capacity** to meet increased metabolic demands during exercise. *0 - 50 %* - This range represents a very **limited increase** in cardiac output and would be indicative of significant underlying cardiac impairment or **heart failure**. - A healthy individual would experience a much greater increase in cardiac output during intense activity than this small percentage. *50 - 100 %* - This range also suggests a **suboptimal cardiac response** for a healthy adult undergoing intense physical activity. - While some increase is present, it does not reflect the full capacity of a healthy cardiovascular system to adapt to extreme demands. *100 - 200 %* - While a 100-200% increase is substantial, it still **underestimates the maximal capacity** achievable in a healthy, well-conditioned individual during intense physical exertion. - The heart has a greater capacity for increasing its output to meet metabolic demands during peak exercise.

Question 866: What is the normal mean velocity of blood flow in the aorta?

A. 100-150 cm/sec
B. 200-250 cm/sec
C. 250-300 cm/sec
D. 40-50 cm/sec (Correct Answer)

Explanation: ***40-50 cm/sec*** - This range represents the **normal mean velocity** of blood flow in the **aorta**, reflecting efficient cardiac output and systemic circulation. - Blood flow velocity can vary slightly based on factors like age, cardiac health, and physical activity, but this range is a common physiological benchmark. *100-150 cm/sec* - This velocity is significantly **higher** than normal for mean aortic flow and would typically indicate a state of **hyperdynamic circulation** or specific pathological conditions. - Such elevated velocities might be seen in conditions like severe **aortic stenosis**, where the heart works harder to push blood through a narrowed valve. *200-250 cm/sec* - This range is **pathologically high** for mean aortic blood flow and is not compatible with normal physiological function. - Velocities in this range would strongly suggest a severe **cardiovascular abnormality**, such as critical **aortic stenosis** or a significant **arteriovenous shunt**. *250-300 cm/sec* - This velocity is **extremely high** and far exceeds any normal or even most pathological mean aortic flow rates found in humans. - Such high velocities would likely be associated with a highly turbulent and severely compromised cardiovascular system, potentially leading to **acute circulatory failure**.

Question 867: Which hormone is primarily responsible for regulating blood pressure in response to significant blood loss due to hemorrhage?

A. Vasopressin (ADH)
B. Aldosterone
C. Epinephrine (Adrenaline) (Correct Answer)
D. Atrial Natriuretic Peptide (ANP)

Explanation: ***Epinephrine (Adrenaline)*** - Released rapidly from the **adrenal medulla** within seconds of hemorrhage as part of the **sympathetic-adrenal response** - Acts as the **primary immediate hormonal response** to severe blood loss, triggering the acute stress response - **Increases heart rate and contractility** (β1 receptors), causes **vasoconstriction** in peripheral vessels (α1 receptors), and **bronchodilation** (β2 receptors) - These combined effects rapidly **maintain blood pressure** and ensure perfusion to vital organs (heart, brain) - Represents the classic **fight-or-flight hormonal response** to acute hemorrhagic stress *Vasopressin (ADH)* - Also plays a **significant role** in hemorrhagic response, with levels increasing dramatically (up to 50-100 fold) - At high concentrations during severe hemorrhage, ADH acts as a **potent vasoconstrictor** via V1 receptors on vascular smooth muscle - Additionally promotes **water reabsorption** in kidneys via V2 receptors to help restore blood volume - However, while vasopressin contributes importantly to blood pressure maintenance, **epinephrine represents the primary immediate hormonal response** in the acute phase - The combined sympathetic-adrenal (catecholamine) response is traditionally considered the first-line hormonal defense *Aldosterone* - A **mineralocorticoid** involved in **longer-term regulation** of blood pressure and volume - Promotes **sodium and water reabsorption** in the distal tubules and collecting ducts, along with **potassium excretion** - Its effects take **hours to days** to manifest, making it important for sustained volume restoration but not the primary acute response to hemorrhage - Part of the RAAS (Renin-Angiotensin-Aldosterone System) activated after hemorrhage *Atrial Natriuretic Peptide (ANP)* - Released from atrial myocytes in response to **atrial stretch** from high blood volume and pressure - Promotes **vasodilation**, **sodium and water excretion** (natriuresis and diuresis), and inhibits renin and aldosterone - Its actions are **counterproductive** during hemorrhage, as they would further lower blood pressure and volume - ANP levels typically **decrease** during hemorrhage, not increase

Question 868: When blood pressure falls below 40 mm Hg, which mechanism of regulation is working?

A. CNS ischemic reflex (Correct Answer)
B. Chemoreceptor response
C. Baroreceptor response
D. None of the options

Explanation: ***CNS ischemic reflex*** - The **CNS ischemic reflex** is activated when blood pressure falls below 60 mmHg, with maximal activation below 40 mmHg, indicating severe ischemia in the brain's vasomotor center. - This reflex elicits an intense **sympathetic vasoconstriction** and cardiac stimulation to prioritize blood flow to the brain even at the expense of other organs. *Chemoreceptor response* - The chemoreceptor reflex is primarily activated by a decrease in **arterial pO2**, an increase in **pCO2**, or a decrease in **pH**. - While it can increase blood pressure, it is not the primary or most profound regulatory mechanism specifically triggered by extremely low blood pressure (below 40 mmHg) to prevent brain ischemia. *Baroreceptor response* - **Baroreceptors** are most sensitive to changes in blood pressure within the normal to moderately hypotensive range (e.g., 60-180 mmHg). - At very low pressures (below 40-50 mmHg), baroreceptors become **less sensitive** or "saturated," and their effectiveness in raising blood pressure significantly diminishes. *None of the options* - This option is incorrect because the **CNS ischemic reflex** specifically functions as a powerful, last-ditch mechanism to maintain cerebral blood flow during severe hypotension which is a life saving reflex during conditions like hemorrhage.

Question 869: What is the critical closing pressure in the context of capillary physiology?

A. Arterial pressure minus venous pressure
B. Capillary pressure minus venous pressure
C. Pressure below which capillaries close (Correct Answer)
D. None of the options

Explanation: ***Pressure below which capillaries close*** - The **critical closing pressure** is the lowest pressure at which blood can flow through a capillary. - When the luminal pressure falls below this threshold, the capillary collapses due to **extrinsic tissue pressure** and intrinsic vascular tone. *Arterial pressure minus venous pressure* - This calculation represents the **arteriovenous pressure gradient**, which drives blood flow through a vascular bed. - It does not directly define the point at which capillaries collapse. *Capillary pressure minus venous pressure* - This difference primarily influences filtration and reabsorption of fluids across the capillary wall. - It is not directly related to the **critical closing pressure** of the capillaries. *None of the options* - This is incorrect as one of the provided options accurately defines the **critical closing pressure**.

Question 870: P wave is due to:

A. Atrial depolarization (Correct Answer)
B. Atrial repolarization
C. Ventricular depolarization
D. Ventricular repolarization

Explanation: **Atrial depolarization** - The **P wave** on an electrocardiogram (ECG) represents the electrical activity associated with the **depolarization of the atria**. - This depolarization leads to **atrial contraction**, pushing blood into the ventricles. *Atrial repolarization* - **Atrial repolarization** also occurs but is usually hidden within the **QRS complex** and thus not separately visible as a distinct wave on a standard ECG. - While it's an electrical event, it does not produce the P wave. *Ventricular depolarization* - **Ventricular depolarization** is represented by the **QRS complex** on an ECG. - This electrical activity leads to **ventricular contraction**, pumping blood out of the heart. *Ventricular repolarization* - **Ventricular repolarization** is represented by the **T wave** on an ECG. - This process allows the ventricles to relax and refill with blood.

Practice by Chapter

Cardiac Electrophysiology

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Cardiac Cycle

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Cardiac Output and Its Regulation

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Hemodynamics and Blood Flow

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Arterial System Physiology

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Microcirculation and Lymphatics

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Venous Return and Central Venous Pressure

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Cardiovascular Reflexes

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Regional Circulations

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Cardiovascular Responses to Exercise and Stress

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