Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 791: Which type of blood vessel is primarily responsible for regulating blood flow to different tissues by varying resistance?

A. Arteries
B. Veins
C. Arterioles (Correct Answer)
D. Capillaries

Explanation: ***Arterioles*** - **Arterioles** are small muscular blood vessels that are the primary sites of **vascular resistance** due to their ability to constrict and dilate. - This **vasoconstriction** and **vasodilation** allows them to regulate blood flow to specific capillary beds and ultimately to different tissues, matching metabolic demands. *Arteries* - **Arteries** are large-diameter vessels that transport **high-pressure blood** away from the heart to the arterioles. - While they contribute to overall resistance, their primary role is less about **fine-tuning** regional flow compared to arterioles. *Veins* - **Veins** are responsible for returning **deoxygenated blood** to the heart and act as a **blood reservoir**. - They have thinner walls and lower pressure than arteries and arterioles, and their capacitance, not resistance, is their primary regulatory function. *Capillaries* - **Capillaries** are the smallest blood vessels, specialized for **exchange of gases, nutrients, and waste products** between blood and tissues. - They have very thin walls and a large surface area for efficient exchange, but their role in regulating blood flow resistance is minimal.

Question 792: What are the expected changes in the pressure-volume loop of the cardiac cycle in a patient with systolic heart failure?

A. Increased end-systolic volume and decreased stroke volume. (Correct Answer)
B. Decreased end-systolic volume and increased stroke volume.
C. Increased end-diastolic volume and increased stroke volume.
D. Decreased end-diastolic volume and decreased stroke volume.

Explanation: **Increased end-systolic volume and decreased stroke volume in systolic heart failure.** - In **systolic heart failure**, the heart's ability to contract effectively is impaired, leading to a **larger volume of blood remaining in the ventricle** after systole (increased end-systolic volume). - This reduced contractile function also means that **less blood is ejected with each beat**, resulting in a **decreased stroke volume** despite potentially normal or increased end-diastolic volumes. *Decreased end-systolic volume and increased stroke volume.* - A **decreased end-systolic volume** would indicate improved ventricular emptying, which is contrary to the definition of **systolic heart failure**. - An **increased stroke volume** would imply better cardiac output, which is not characteristic of systolic heart failure. *Increased end-diastolic volume and increased stroke volume.* - While **increased end-diastolic volume** can occur in heart failure as a compensatory mechanism (Preload), **increased stroke volume** would indicate improved cardiac function, which is not the case in systolic heart failure. - In systolic heart failure, the heart struggles to eject blood despite a larger filling volume, so stroke volume would typically be reduced. *Decreased end-diastolic volume and decreased stroke volume.* - **Decreased end-diastolic volume** is more characteristic of **diastolic heart failure** (impaired filling) or significant hypovolemia, not the primary issue in systolic heart failure. - While stroke volume is indeed decreased in systolic heart failure, the primary defect is in ejection, not necessarily reduced ventricular filling (end-diastolic volume).

Question 793: Which reflex is primarily activated in response to an increase in venous return to the heart?

A. Bainbridge reflex (Correct Answer)
B. Baroreceptor reflex
C. Chemoreceptor reflex
D. Bezold-Jarisch reflex

Explanation: ***Bainbridge reflex*** - The **Bainbridge reflex** is triggered by an increase in **venous return** and consequent stretching of the right atrial wall. - This reflex leads to an increase in **heart rate**, primarily to prevent blood from pooling in the atria and accommodate the increased volume. *Baroreceptor reflex* - The **baroreceptor reflex** is primarily involved in regulating **arterial blood pressure** by responding to changes in stretch in the carotid sinus and aortic arch. - It works to maintain blood pressure homeostasis by altering **heart rate** and **peripheral vascular resistance**. *Chemoreceptor reflex* - The **chemoreceptor reflex** is activated by changes in **blood pH, PCO2, and PO2**, primarily to regulate respiration and, secondarily, blood pressure. - It is sensitive to **hypoxia, hypercapnia, and acidosis**, and its main goal is to restore normal blood gas levels. *Bezold-Jarisch reflex* - The **Bezold-Jarisch reflex** is a cardiac reflex characterized by **bradycardia, vasodilation, and hypotension**. - It is typically activated by strong stimulation of ventricular mechanoreceptors, often in situations of **myocardial ischemia** or severe cardiac stress.

Question 794: An increase in cardiac output during exercise is primarily achieved through which mechanism?

A. Increased stroke volume
B. Decreased venous return
C. Decreased sympathetic activity
D. Increased heart rate (Correct Answer)

Explanation: ***Increased heart rate*** - During exercise, cardiac output (CO = HR × SV) increases primarily through **marked elevation in heart rate**, which can increase **3-4 fold** (from ~70 bpm to 180-200 bpm in maximal exercise). - Heart rate contributes approximately **60-70% of the total increase** in cardiac output during exercise. - **Sympathetic stimulation** and **decreased parasympathetic tone** rapidly increase heart rate to meet the body's metabolic demands. - While stroke volume also increases, it plateaus at moderate exercise intensity (~40-60% of maximum capacity), whereas heart rate continues to rise linearly with exercise intensity. *Increased stroke volume* - Stroke volume does increase during exercise through the **Frank-Starling mechanism** (increased venous return) and **enhanced contractility** (sympathetic stimulation). - However, stroke volume increases by only **20-50%** and contributes approximately **30-40% of the total increase** in cardiac output. - Stroke volume reaches a **plateau at submaximal exercise levels**, while heart rate continues to increase, making heart rate the **quantitatively dominant mechanism**. *Decreased venous return* - This would **decrease cardiac output**, not increase it. - During exercise, venous return actually **increases dramatically** due to the **skeletal muscle pump**, **respiratory pump**, and **venoconstriction**. *Decreased sympathetic activity* - This would lead to **decreased heart rate and contractility**, reducing cardiac output. - Exercise is characterized by **increased sympathetic activity** and **decreased parasympathetic activity** to enhance cardiovascular performance.

Question 795: A patient with chronic liver disease presents with ascites. What is the primary physiological mechanism for the development of ascites in this condition?

A. Increased plasma albumin
B. Increased lymphatic drainage
C. Increased capillary hydrostatic pressure (Correct Answer)
D. Decreased capillary permeability

Explanation: ***Increased capillary hydrostatic pressure*** - **Portal hypertension**, a common complication of chronic liver disease, leads to increased pressure in the **hepatic portal system**. - This elevated pressure translates to increased capillary hydrostatic pressure within the splanchnic circulation, forcing fluid out of the capillaries and into the peritoneal cavity, forming **ascites**. *Increased plasma albumin* - Chronic liver disease typically leads to **decreased synthesis of albumin** (hypoalbuminemia), not increased levels. - Reduced albumin would lower plasma oncotic pressure, contributing to fluid extravasation, not opposing it. *Increased lymphatic drainage* - While lymphatic drainage does increase in an attempt to compensate for increased fluid extravasation, it eventually becomes **overwhelmed** in chronic liver disease. - The primary mechanism for the accumulation of fluid is the leakage from capillaries, not an initial increase in drainage. *Decreased capillary permeability* - **Decreased capillary permeability** would actually restrict fluid movement out of capillaries, thus preventing or reducing ascites formation. - In chronic liver disease and portal hypertension, capillary permeability can even be **increased**, which would further contribute to fluid leakage.

Question 796: During the cardiac cycle, the period immediately following the closure of the aortic valve is called:

A. Isovolumetric contraction
B. Isovolumetric relaxation (Correct Answer)
C. Rapid filling phase
D. Reduced filling phase

Explanation: ***Isovolumetric relaxation*** - This phase begins immediately after the **closure of the aortic and pulmonary valves** (marking the end of systole) and before the opening of the mitral and tricuspid valves. - During this period, the ventricles **relax without a change in volume**, causing a rapid drop in intraventricular pressure until it falls below atrial pressure. *Isovolumetric contraction* - This phase occurs **before the ejection of blood**, after the closure of the mitral and tricuspid valves and before the opening of the aortic and pulmonary valves. - It involves the ventricles contracting and increasing pressure, but the **volume of blood remains constant**. *Rapid filling phase* - This phase occurs **after isovolumetric relaxation**, once ventricular pressure falls below atrial pressure, causing the mitral and tricuspid valves to open. - During this time, blood flows rapidly from the atria into the ventricles, but it is not immediately after aortic valve closure. *Reduced filling phase* - This is a later stage of ventricular filling, occurring towards the **end of diastole**, where the rate of blood flow from the atria to the ventricles slows down. - It is also known as **diastasis** and is distinct from the events immediately following aortic valve closure.

Question 797: A 50-year-old woman presents with a sudden onset of severe headache and visual disturbances. Her blood pressure is 210/130 mmHg. Which of the following physiological processes is most likely contributing to her symptoms?

A. Cerebral autoregulation failure (Correct Answer)
B. Increased cerebral perfusion due to hypertension
C. Decreased intracranial pressure due to fluid shifts
D. Cerebral vasoconstriction in response to high blood pressure

Explanation: ***Cerebral autoregulation failure*** - With **severe hypertension** (210/130 mmHg), the brain's ability to maintain a constant **cerebral blood flow** can be overwhelmed. - This leads to loss of vascular tone, allowing excessive blood flow and **cerebral edema**, causing symptoms like headache and visual disturbances. *Increased cerebral perfusion due to hypertension* - While hypertension does lead to increased perfusion pressure, the direct cause of symptoms is the **failure of autoregulation** to compensate and protect the brain from this increased pressure. - The brain normally compensates for moderate increases in blood pressure through **vasoconstriction** to maintain stable cerebral blood flow. *Decreased intracranial pressure due to fluid shifts* - **Severe hypertension** typically leads to **increased intracranial pressure** due to vasogenic edema, not decreased ICP. - Reduced ICP would generally alleviate headache and visual disturbances, not cause them. *Cerebral vasoconstriction in response to high blood pressure* - **Cerebral vasoconstriction** is part of the normal autoregulatory response to mild-to-moderate hypertension, aiming to protect the brain from excessive blood flow. - In severe hypertension, this autoregulatory mechanism **fails**, leading to vasodilation and hyperperfusion.

Question 798: The Frank-Starling mechanism in the heart refers to the relationship between:

A. Heart rate and stroke volume
B. Venous return and cardiac output
C. Preload and stroke volume (Correct Answer)
D. Afterload and cardiac output

Explanation: ***Preload and stroke volume*** - The **Frank-Starling mechanism** states that the **stroke volume** of the heart increases in response to an increase in the **volume of blood filling the heart (preload)**, when all other factors remain constant. - This mechanism allows the heart to **match cardiac output to venous return**, ensuring that the heart pumps out the blood it receives. *Heart rate and stroke volume* - While both **heart rate** and **stroke volume** determine cardiac output (Cardiac Output = Heart Rate × Stroke Volume), the Frank-Starling mechanism specifically describes the heart's intrinsic ability to adjust stroke volume in response to filling pressure. - Changes in heart rate are extrinsic regulations and do not directly define the Frank-Starling mechanism, which is an intrinsic property of myocardial contractility. *Venous return and cardiac output* - **Venous return** significantly influences **cardiac output** through its effect on preload, which then affects stroke volume via the Frank-Starling mechanism. - However, the Frank-Starling law describes the direct relationship at the ventricular level, linking **end-diastolic volume (preload)** to the **force of contraction (stroke volume)**. *Afterload and cardiac output* - **Afterload** (the resistance the heart must overcome to eject blood) inversely affects stroke volume and thus cardiac output. - The Frank-Starling mechanism explains how the heart adjusts to changes in **volume (preload)**, not primarily to changes in resistance (afterload).

Question 799: Which layer of the heart is primarily responsible for the conduction of electrical impulses?

A. Epicardium
B. Pericardium
C. Endocardium
D. Myocardium (Correct Answer)

Explanation: ***Myocardium*** - The **myocardium** is the thick muscular layer of the heart that contains the entire **cardiac conduction system**, including the SA node, AV node, Bundle of His, bundle branches, and Purkinje fibers. - These specialized **myocardial cells** form the conduction pathways that rapidly transmit electrical impulses throughout the heart, coordinating atrial and ventricular contractions. - The Purkinje fibers, while located in the subendocardial region, are specialized **myocardial cells**, not endocardial tissue. *Endocardium* - The **endocardium** is the thin innermost endothelial lining of the heart chambers and valves. - While Purkinje fibers lie just beneath the endocardium (subendocardial), the endocardium itself is not a conductive layer but rather a smooth lining that reduces friction. *Epicardium* - The **epicardium** is the outermost layer of the heart wall (visceral pericardium) and serves as a protective covering. - It contains coronary vessels and autonomic nerve fibers but does not contain the specialized conduction system. *Pericardium* - The **pericardium** is the fibroserous sac surrounding the heart that provides protection and prevents overdistension. - It has no role in electrical impulse generation or conduction within the heart.

Question 800: What is the body's most immediate response to significant hemorrhage?

A. Vasodilation
B. Vasoconstriction (Correct Answer)
C. Increased urine output
D. Decreased heart rate

Explanation: ***Vasoconstriction*** - In response to a significant drop in **blood volume and pressure**, the body **immediately** triggers **baroreflexes** and sympathetic nervous system activation within **seconds**. - This leads to systemic **vasoconstriction** in peripheral vascular beds (splanchnic, renal, cutaneous) to shunt blood to vital organs and maintain central blood pressure. - This is the **fastest compensatory mechanism**, mediated by neural pathways, making it the most immediate response. *Vasodilation* - **Vasodilation** would further lower blood pressure and worsen the effects of hemorrhage, as it would decrease systemic vascular resistance. - This response is typically seen in conditions like **sepsis** or allergic reactions, not hemorrhagic shock. *Increased urine output* - In hemorrhage, the body attempts to **conserve fluid**, leading to a significant **decrease in urine output** due to renal vasoconstriction and ADH release. - Increased urine output would exacerbate fluid loss, which is counterproductive in this situation. *Decreased heart rate* - The initial and most common cardiac response to hemorrhage is **tachycardia** (increased heart rate) to compensate for reduced stroke volume and maintain cardiac output. - A decreased heart rate would further reduce cardiac output and worsen tissue perfusion.

Practice by Chapter

Cardiac Electrophysiology

Practice Questions

Cardiac Cycle

Practice Questions

Cardiac Output and Its Regulation

Practice Questions

Hemodynamics and Blood Flow

Practice Questions

Arterial System Physiology

Practice Questions

Microcirculation and Lymphatics

Practice Questions

Venous Return and Central Venous Pressure

Practice Questions

Cardiovascular Reflexes

Practice Questions

Regional Circulations

Practice Questions

Cardiovascular Responses to Exercise and Stress

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free