Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 811: Which heart chamber pumps oxygenated blood to the systemic circulation?

A. Right atrium
B. Right ventricle
C. Left atrium
D. Left ventricle (Correct Answer)

Explanation: ***Left ventricle*** - The **left ventricle** receives **oxygenated blood** from the left atrium and has the thickest muscular wall to pump this blood with high pressure into the **aorta** for distribution throughout the body. - Its powerful contractions are essential for maintaining systemic blood flow and delivering oxygen to all tissues. *Right atrium* - The right atrium receives **deoxygenated blood** from the systemic circulation via the **superior and inferior vena cavae**. - It pumps blood into the right ventricle, not into the systemic circulation. *Right ventricle* - The right ventricle pumps **deoxygenated blood** to the **pulmonary arteries** for oxygenation in the lungs. - Its function is limited to the **pulmonary circulation**, not the systemic circulation. *Left atrium* - The left atrium receives **oxygenated blood** from the lungs via the **pulmonary veins**. - It delivers blood to the left ventricle but does not pump directly into the systemic circulation.

Question 812: Cerebral blood flow is regulated by all of the following except:

A. Calcium ions (Correct Answer)
B. Blood pressure
C. Arterial PCO2
D. Potassium ions

Explanation: ***Calcium ions*** - While **calcium ions (Ca²⁺)** are mechanistically essential for vascular smooth muscle contraction and relaxation, they are **not considered a primary regulatory signal** for cerebral blood flow (CBF) in the same way as the other factors listed. - Ca²⁺ acts as an **intracellular second messenger** that mediates the effects of other regulatory factors (like PCO2, K⁺, and vasoactive substances), rather than being a direct extracellular regulatory signal itself. - The question refers to primary regulatory factors that directly modulate CBF, not the intracellular mechanisms by which vascular smooth muscle responds. *Blood pressure* - **Cerebral autoregulation** maintains relatively constant CBF despite changes in **mean arterial pressure (MAP)** between approximately 60-150 mmHg. - Blood pressure is a **key regulatory factor** - when MAP falls below or exceeds this range, CBF becomes pressure-dependent. - This protective mechanism prevents cerebral ischemia or hyperemia with systemic blood pressure fluctuations. *Arterial PCO2* - **Arterial partial pressure of carbon dioxide (PaCO2)** is one of the **most potent direct regulators** of CBF. - **Hypercapnia** (increased PaCO2) causes cerebral vasodilation and increased CBF (approximately 1-2 mL/100g/min increase per 1 mmHg rise in PaCO2). - **Hypocapnia** (decreased PaCO2) causes vasoconstriction and reduced CBF, utilized therapeutically in managing elevated intracranial pressure. *Potassium ions* - **Increased extracellular K⁺** in the perivascular space causes **direct vasodilation** of cerebral arterioles. - This mechanism is crucial for **neurovascular coupling** (functional hyperemia) - when neurons are active, they release K⁺, which dilates nearby vessels to increase local blood flow. - K⁺-mediated vasodilation helps match cerebral perfusion to metabolic demand during neuronal activity.

Question 813: Closure of patent ductus arteriosus is stimulated by?

A. Prostaglandin F2a
B. Hypercarbia
C. Cyclooxygenase
D. Increase in O2 tension at birth (Correct Answer)

Explanation: ***Increase in O2 tension at birth*** - The **patent ductus arteriosus (PDA)** remains open during fetal life due to low oxygen tension and elevated **prostaglandin E2** levels. - At birth, the first breath significantly increases **pulmonary blood flow** and **arterial oxygen tension**, leading to constriction and functional closure of the PDA. *Prostaglandin F2a* - While prostaglandins play a crucial role in vascular tone, **prostaglandin F2a** is not the primary mediator for PDA closure. - **Prostaglandin E2** is primarily responsible for keeping the ductus arteriosus open in utero. *Cyclooxygenase* - **Cyclooxygenase (COX)** is an enzyme involved in the synthesis of prostaglandins. - While inhibitors of COX (e.g., indomethacin) can induce PDA closure by reducing prostaglandin synthesis, COX itself does not directly stimulate closure. *Hypercarbia* - **Hypercarbia** (elevated CO2 levels) is typically associated with **vasodilation**, particularly in the cerebral circulation, and would not promote PDA closure. - It does not directly impact the mechanisms responsible for the constriction of the ductus arteriosus.

Question 814: Immediate physiological response to sudden decrease in blood volume is

A. Release of angiotensin
B. Release of thyroxine
C. Release of epinephrine (Correct Answer)
D. Shift of fluid from intracellular to interstitial compartment

Explanation: ***Release of epinephrine*** - A sudden decrease in blood volume triggers the **sympathetic nervous system** to release **epinephrine** (and norepinephrine) from the adrenal medulla. - Epinephrine causes **vasoconstriction** and increases **heart rate** and **contractility** to maintain blood pressure and cardiac output. *Release of angiotensin* - **Angiotensin** is part of the **renin-angiotensin-aldosterone system (RAAS)**, which is activated in response to decreased blood volume and renal perfusion. - While important for long-term blood pressure regulation and fluid balance, its release is not the **immediate physiological response** compared to catecholamines. *Release of thyroxine* - **Thyroxine** (thyroid hormone) primarily regulates **metabolism** and is not involved in the immediate compensatory mechanisms for sudden blood volume changes. - Its effects are **slow** and long-lasting, unlike the rapid response needed. *Shift of fluid from intracellular to interstitial compartment* - Fluid shifts due to changes in **osmolarity** or **hydrostatic pressure** do occur, but the immediate response to a sudden volume decrease involves **neurohormonal activation**. - A shift from the **intracellular** to the **extracellular** (interstitial and intravascular) compartment would actually help restore blood volume, but this is a *consequence* of compensatory mechanisms, not the primary and immediate physiological *response*.

Question 815: What is the purpose of the square wave seen in an ECG recording?

A. Indicates atrial depolarization
B. Indicates ventricular depolarization
C. Indicates ventricular repolarization
D. Used for standardization of ECG (Correct Answer)

Explanation: ***Used for standardization of ECG*** - The **square wave** at the beginning of an ECG tracing is a **calibration signal**, typically 1 mV in amplitude and 0.2 seconds in duration. - It ensures that the ECG machine is accurately recording the electrical activity, allowing for proper measurement of subsequent waveforms. *Indicates atrial depolarization* - **Atrial depolarization** is represented by the **P wave** on the ECG, which is a small, rounded wave preceding the QRS complex. - The square wave serves a technical purpose for calibration, not a physiological one related to cardiac electrical activity. *Indicates ventricular depolarization* - **Ventricular depolarization** is represented by the **QRS complex**, which is a sharp, prominent deflection following the P wave. - This complex reflects the rapid electrical activation of the ventricles, very different from the calibration square wave. *Indicates ventricular repolarization* - **Ventricular repolarization** is represented by the **T wave**, which is typically a rounded wave following the QRS complex. - This physiological event is distinct from the initial square wave, which is an artifact generated by the ECG device for calibration.

Question 816: Which of the following hemodynamic changes is not evident in cardiac tamponade during diastole?

A. Right atrial and ventricular collapse
B. Absent y wave on JVP
C. Biphasic venous return (Correct Answer)
D. Elevated pericardial pressure

Explanation: ***Biphasic venous return*** - In **normal conditions**, the jugular venous pulse (JVP) shows a **biphasic pattern** with two descents: the **'x' descent** (atrial relaxation) and the **'y' descent** (rapid ventricular filling). - In **cardiac tamponade**, the elevated intrapericardial pressure prevents effective right ventricular filling during diastole, causing the **'y' descent to be absent or markedly blunted**. - This results in a **monophasic pattern** (only 'x' descent visible), meaning **true biphasic venous return is NOT evident** in cardiac tamponade. - This is the hemodynamic change that is **not present** during diastole in tamponade. *Right atrial and ventricular collapse* - This **IS a hallmark feature** observed in cardiac tamponade via echocardiography, particularly during diastole. - The increased intrapericardial pressure compresses the thin-walled right-sided chambers, causing them to collapse during diastole. *Absent y wave on JVP* - The **'y' descent** on the JVP represents the rapid ventricular filling phase after the tricuspid valve opens. - In cardiac tamponade, the elevated intrapericardial pressure prevents effective right ventricular filling, thus **blunting or completely abolishing the 'y' descent**. - This finding **IS evident** in cardiac tamponade. *Elevated pericardial pressure* - This **IS the fundamental physiological change** in cardiac tamponade, as the accumulation of fluid in the pericardial sac raises the pressure. - This elevated pressure compresses the cardiac chambers and impedes diastolic filling, particularly affecting the right atrium and ventricle due to their lower filling pressures.

Question 817: Which of the following is considered the most important cerebral vasodilator in physiological conditions?

A. Hydrogen ions (H+)
B. Carbon dioxide (CO2) (Correct Answer)
C. Sodium ions (Na+)
D. Calcium ions (Ca2+)

Explanation: ***Carbon dioxide (CO2)*** - CO2 is the **most important physiological cerebral vasodilator** under normal conditions - CO2 diffuses readily across the blood-brain barrier into brain tissue - It forms carbonic acid (H2CO3), which dissociates to H+ and HCO3-, decreasing **extracellular pH** - This pH change directly relaxes cerebral arterioles, increasing cerebral blood flow - Even small changes in PaCO2 (arterial CO2 tension) cause significant alterations in cerebral blood flow *Hydrogen ions (H+)* - While hydrogen ions directly influence cerebral vasodilation by affecting pH, they are primarily generated from **CO2 metabolism** - H+ ions do not cross the blood-brain barrier as readily as CO2 - The direct effect of H+ is secondary to CO2's role, making H+ an important downstream mediator rather than the primary trigger *Sodium ions (Na+)* - Sodium ions play critical roles in **neuronal excitation** and **membrane potential maintenance** - They are not directly involved in the physiological regulation of cerebral blood vessel tone - Changes in Na+ concentration do not directly cause vasodilation or constriction in cerebral arteries under normal conditions *Calcium ions (Ca2+)* - Calcium ions are crucial for **vascular smooth muscle contraction** - Increased intracellular Ca2+ leads to vasoconstriction, while decreased Ca2+ promotes vasodilation - However, Ca2+ is a mediator of smooth muscle contraction/relaxation rather than the primary physiological stimulus for cerebral vasodilation

Question 818: What is the effect of positive G-force on cardiac output?

A. Increased cerebral arterial pressure due to G-force
B. Increased venous return due to G-force
C. Increased pressure in lower limb due to G-force
D. Decreased cardiac output due to G-force (Correct Answer)

Explanation: ***Decreased cardiac output due to G-force*** - **Positive G-forces** push blood downwards towards the lower extremities, leading to a significant **reduction in venous return** to the heart. - Reduced venous return directly translates to a **decreased preload** and subsequently a **decreased cardiac output**, as less blood is available for pumping. *Increased cerebral arterial pressure due to G-force* - **Positive G-forces** cause blood to pool in the lower body, leading to a **decrease in arterial pressure** in the upper body and brain, not an increase. - This **reduced cerebral perfusion** is the reason for symptoms like **lightheadedness** and **G-LOC (G-induced loss of consciousness)**. *Increased venous return due to G-force* - **Positive G-forces** exert a force on the blood that acts in the same direction as gravity (head-to-foot), actively **pulling blood away from the heart** and into the lower extremities. - This gravitational pooling of blood in the dependent parts of the body significantly **reduces venous return** to the right atrium, rather than increasing it. *Increased pressure in lower limb due to G-force* - While there is indeed **increased hydrostatic pressure** in the lower limbs due to the pooling of blood under positive G-forces, this is a consequence of blood being pulled away from the central circulation. - This increased pressure in the lower limbs does not lead to an increased cardiac output; instead, it's a symptom of the **reduced central blood volume** and **decreased venous return**.

Question 819: Which ion is primarily responsible for initiating the action potential in contractile cardiac muscle cells (atrial and ventricular myocytes)?

A. Calcium (Ca2+)
B. Chloride (Cl-)
C. Potassium (K+)
D. Sodium (Na+) (Correct Answer)

Explanation: ***Sodium (Na+)*** - The rapid influx of **Na+ through fast voltage-gated sodium channels** is responsible for the rapid depolarization phase (Phase 0) of the action potential in contractile cardiac myocytes. - This initial influx quickly brings the membrane potential to a positive value, initiating the action potential. *Potassium (K+)* - While **K+ channels** are crucial for repolarization (Phase 3) and maintaining the resting membrane potential, they do not initiate the action potential. - An efflux of K+ ions causes the membrane potential to become more negative, leading to repolarization. *Calcium (Ca2+)* - **Ca2+ influx** through L-type calcium channels is responsible for the plateau phase (Phase 2) of the action potential, which prolongs the refractory period. - While important for excitation-contraction coupling, Ca2+ does not initiate the rapid depolarization phase. *Chloride (Cl-)* - **Chloride ions** play a more minor role in cardiac action potentials, primarily contributing to some repolarization currents but not to the initial depolarization. - Their primary role is in maintaining cellular osmolarity and charge balance.

Question 820: Baroreceptors are related to which vessels?

A. Carotid sinus (Correct Answer)
B. Subclavian artery
C. External carotid artery
D. Brachiocephalic trunk

Explanation: ***Carotid sinus*** - Baroreceptors are located in the **carotid sinus**, which is a dilated region at the **bifurcation of the common carotid artery** into the internal and external carotid arteries. - These **arterial baroreceptors** detect changes in blood pressure and send signals via the **glossopharyngeal nerve (CN IX)** to the cardiovascular centers in the medulla. - The carotid sinus is one of the two major baroreceptor sites (the other being the aortic arch). *External carotid artery* - While it originates from the common carotid artery at the bifurcation, the **external carotid artery** itself does not contain baroreceptors. - Its main function is to supply blood to the face, scalp, and superficial structures of the head and neck. *Subclavian artery* - The subclavian artery is a major artery supplying the upper limb and does **not contain baroreceptors**. - Its primary role is to supply blood to the arms, chest wall, and neck. *Brachiocephalic trunk* - The brachiocephalic trunk (innominate artery) gives rise to the right common carotid artery and right subclavian artery, but it **does not house baroreceptors**. - Baroreceptors are located more distally in the carotid sinus and aortic arch.

Practice by Chapter

Cardiac Electrophysiology

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Cardiac Cycle

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Cardiac Output and Its Regulation

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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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