Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 771: Which of the following is a FALSE statement regarding hemodynamic changes occurring during exercise?

A. Venous return is augmented by the pumping action of skeletal muscles.
B. End-diastolic volume increases in the failing heart during exercise.
C. Venoconstriction in exercising muscles as well as increased cardiac output leads to marked increase in systemic blood pressure. (Correct Answer)
D. The increased adrenergic nerve impulses to the heart as well as an increased concentration of circulating catecholamines help to augment the contractile state of the myocardium.

Explanation: ***Venoconstriction in exercising muscles as well as increased cardiac output leads to marked increase in systemic blood pressure.*** - This is the **FALSE statement**. During exercise, **vasodilation (not venoconstriction) occurs in exercising muscles** to increase blood flow to active tissues. Venoconstriction occurs in **non-exercising vascular beds** to redistribute blood. - While cardiac output increases significantly, **systemic vascular resistance (SVR) decreases** due to vasodilation in exercising muscles, which counteracts the rise in cardiac output. - The net effect is a **moderate increase in mean arterial pressure**, not a "marked increase." **Systolic BP rises** due to increased cardiac output, but **diastolic BP remains stable or slightly decreases** due to reduced SVR. - Therefore, this statement incorrectly describes both the vascular response in exercising muscles and the magnitude of systemic blood pressure change. *Venous return is augmented by the pumping action of skeletal muscles.* - **TRUE statement**. The **skeletal muscle pump** compresses veins during muscle contraction, pushing blood back toward the heart and increasing venous return. - This mechanism is crucial during exercise to maintain cardiac output and prevent blood pooling in lower extremities. *End-diastolic volume increases in the failing heart during exercise.* - **TRUE statement**. In a **failing heart**, the Frank-Starling mechanism operates on a flatter curve with reduced contractile reserve. - During exercise, increased venous return leads to **increased end-diastolic volume (preload)**, but the failing heart cannot adequately increase stroke volume proportionally, leading to volume accumulation and potential pulmonary congestion. *The increased adrenergic nerve impulses to the heart as well as an increased concentration of circulating catecholamines help to augment the contractile state of the myocardium.* - **TRUE statement**. During exercise, **sympathetic nervous system activation** increases, releasing **norepinephrine from adrenergic nerves** and **epinephrine from the adrenal medulla**. - These **catecholamines** bind to **beta-1 adrenergic receptors** on cardiomyocytes, increasing **heart rate (chronotropy)**, **contractility (inotropy)**, and **conduction velocity (dromotropy)**, thereby enhancing cardiac performance.

Question 772: The major pressures that determine filtration and absorption of fluid by capillaries are the:

A. Plasma colloid osmotic pressure and interstitial hydrostatic pressure
B. Capillary hydrostatic pressure and tissue colloid osmotic pressure
C. Capillary hydrostatic pressure and plasma colloid osmotic pressure (Correct Answer)
D. Interstitial hydrostatic pressure and tissue colloid osmotic pressure

Explanation: ***Capillary hydrostatic pressure and plasma colloid osmotic pressure*** - **Capillary hydrostatic pressure (CHP)** is the primary force favoring **filtration** of fluid out of the capillary into the interstitial space. - **Plasma colloid osmotic pressure (PCOP)** is the main force opposing filtration, drawing fluid back into the capillary due to plasma proteins; it promotes **absorption**. *Plasma colloid osmotic pressure and interstitial hydrostatic pressure* - While plasma colloid osmotic pressure is a major force influencing fluid movement, **interstitial hydrostatic pressure** typically opposes filtration, and is a less dominant force in driving the *net* direction of fluid movement compared to capillary hydrostatic pressure. - This option does not include the primary driving force for filtration, which is **capillary hydrostatic pressure**. *Capillary hydrostatic pressure and tissue colloid osmotic pressure* - **Capillary hydrostatic pressure** promotes filtration, but **tissue colloid osmotic pressure** favors filtration by drawing fluid out of the capillary, which would result in excessive filtration. - This combination lacks the opposing force (plasma colloid osmotic pressure) critical for maintaining fluid balance and absorption. *Interstitial hydrostatic pressure and tissue colloid osmotic pressure* - Both **interstitial hydrostatic pressure** and **tissue colloid osmotic pressure** are forces within the interstitial space. - Neither of these directly represents the primary pushing force from the capillary (capillary hydrostatic pressure) nor the primary pulling force into the capillary (plasma colloid osmotic pressure) that largely govern filtration and absorption.

Question 773: In a fetus highest oxygen concentration is found in?

A. Superior vena cava
B. Umbilical vein (Correct Answer)
C. Left ventricle
D. Ascending aorta

Explanation: ***Umbilical vein*** - The **umbilical vein** carries oxygenated blood from the **placenta**, which serves as the site of gas exchange, making its oxygen concentration the highest in the fetal circulation. - This highly oxygenated blood bypasses the fetal lungs via shunts such as the **ductus venosus** and **foramen ovale** to supply vital organs. *Superior vena cava* - The **superior vena cava** carries deoxygenated blood from the upper body and head back to the heart, mixing with oxygenated blood in the right atrium. - Its blood has a relatively **low oxygen saturation** compared to the umbilical vein. *Left ventricle* - The **left ventricle** receives blood that has already mixed in the atria and passed through the foramen ovale, then the left atrium. - While relatively oxygen-rich for systemic circulation, its oxygen concentration is lower than that in the umbilical vein due to **mixing with deoxygenated blood**. *Ascending aorta* - The **ascending aorta** receives blood from the left ventricle, which has a moderate oxygen content. - The blood in the ascending aorta feeds the upper body, but its oxygen saturation is lower than that in the umbilical vein due to the **physiological shunts** and mixing of blood.

Question 774: Which one of the following is a function of PGI2?

A. Causes blood vessel constriction and prevents platelet clumping
B. Causes blood vessel constriction and promotes platelet clumping
C. Causes blood vessel relaxation and prevents platelet clumping (Correct Answer)
D. Causes blood vessel relaxation and promotes platelet clumping

Explanation: **Correct Answer: Causes blood vessel relaxation and prevents platelet clumping** ***PGI2 (prostacyclin)*** is a potent **vasodilator** produced by vascular endothelium that causes blood vessel relaxation. It also has a powerful inhibitory effect on **platelet aggregation**, thus preventing platelet clumping and thrombosis. These two functions make PGI2 an important anti-thrombotic mediator in the cardiovascular system. *Incorrect: Causes blood vessel constriction and prevents platelet clumping* - This option is incorrect because PGI2 **relaxes blood vessels** (vasodilation), it does not constrict them. - While it correctly states that PGI2 prevents platelet clumping, its effect on blood vessels is wrongly stated. *Incorrect: Causes blood vessel constriction and promotes platelet clumping* - This statement is entirely incorrect as PGI2's functions are the opposite: **vasodilation** and **inhibition of platelet aggregation**. - **Thromboxane A2 (TXA2)** is an eicosanoid with these described effects (constricts blood vessels and promotes platelet clumping), making it the functional antagonist of PGI2. *Incorrect: Causes blood vessel relaxation and promotes platelet clumping* - While PGI2 does cause **blood vessel relaxation** (vasodilation), it actively **prevents platelet clumping** rather than promoting it. - Promotion of platelet clumping is a function of other substances like **Thromboxane A2 (TXA2)**.

Question 775: Which centre first gets the input from neural control of cardiovascular system?

A. NTS (Correct Answer)
B. Raphe Nucleus
C. RVLM
D. Nucleus ambiguus

Explanation: ***NTS (Nucleus Tractus Solitarius)*** - The **NTS** is the primary medullary relay nucleus for **baroreceptor** and **chemoreceptor afferent inputs**, making it the first center to receive information regarding cardiovascular status. - It integrates sensory information from the **glossopharyngeal (CN IX)** and **vagus (CN X)** nerves. *Raphe Nucleus* - The **raphe nuclei** are a collection of nuclei in the brainstem that primarily play a significant role in modulating **serotonin release**, affecting mood, sleep, and pain. - They are not the initial receiving centers for primary cardiovascular sensory inputs. *RVLM (Rostral Ventrolateral Medulla)* - The **RVLM** is a crucial site for generating **sympathetic vasomotor tone** and is influenced by the NTS. - While essential for cardiovascular control, it receives its primary regulatory input from the NTS and is not the *initial* input center. *Nucleus ambiguus* - The **nucleus ambiguus** contains **preganglionic parasympathetic neurons** that project to the heart (via the vagus nerve) to decrease heart rate. - It receives input from the NTS for cardiovascular regulation but is not the first structure to process afferent cardiovascular information.

Question 776: True about Postural Hypotension:

A. Decreases in systolic blood pressure 20 mmHg within 6 minutes.
B. Decreases in diastolic blood pressure 20 mmHg within 6 minutes.
C. Decreases in diastolic blood pressure 20 mmHg within 3 minutes.
D. Decreases in systolic blood pressure 20 mmHg within 3 minutes. (Correct Answer)

Explanation: ***Decreases in systolic blood pressure 20 mmHg within 3 minutes.*** - **Postural hypotension** (or orthostatic hypotension) is defined as a fall in **systolic blood pressure** of at least **20 mmHg** OR a fall in **diastolic blood pressure** of at least **10 mmHg** upon standing. - This drop in blood pressure must occur within **3 minutes** of assuming an upright position from a supine or seated position. - This is the standard diagnostic criterion per American Autonomic Society and European Society of Cardiology guidelines. *Decreases in systolic blood pressure 20 mmHg within 6 minutes.* - While a drop of 20 mmHg in systolic blood pressure is the correct magnitude, the timeframe of **6 minutes** exceeds the standard diagnostic criterion of **3 minutes**. - A delayed drop might indicate other cardiovascular issues or a less pronounced form of orthostatic intolerance, but does not meet the classic definition of postural hypotension. *Decreases in diastolic blood pressure 20 mmHg within 6 minutes.* - This option is incorrect on two counts: the diastolic criterion is **10 mmHg** (not 20 mmHg), and the timeframe is **6 minutes** (not 3 minutes). - While a 20 mmHg drop in diastolic pressure would certainly be significant, it is not the standard diagnostic criterion. *Decreases in diastolic blood pressure 20 mmHg within 3 minutes.* - While the timeframe of **3 minutes** is correct, the diastolic criterion for postural hypotension is a drop of **10 mmHg**, not 20 mmHg. - A 20 mmHg drop in diastolic blood pressure would be a more severe finding, but the standard definition uses 10 mmHg as the threshold.

Question 777: Baroreceptor is which type of feedback?

A. Feed forward control
B. Negative feedback (Correct Answer)
C. Positive feedback
D. Both negative and positive

Explanation: ***Negative feedback*** - The **baroreceptor reflex** detects changes in blood pressure and initiates responses that **counteract** the change, bringing blood pressure back to its set point - For example, if blood pressure increases, baroreceptors signal the brainstem to **decrease heart rate** and **dilate blood vessels**, thus lowering blood pressure - This is the **primary mechanism** for maintaining cardiovascular homeostasis *Feed forward control* - This type of control **anticipates** future disturbances and makes adjustments **before** the disturbance can significantly affect the system - The baroreceptor reflex specifically responds to **current** pressure changes detected by the receptors, not predicted future changes *Positive feedback* - Positive feedback mechanisms **amplify** the initial stimulus, moving the system further **away** from the set point - Examples include blood clotting cascade and uterine contractions during childbirth - Blood pressure regulation via baroreceptors aims for **stability**, not amplification *Both negative and positive* - While some physiological systems can exhibit both types of feedback under different circumstances, the baroreceptor reflex operates **exclusively** through negative feedback - The primary function is to maintain **homeostasis** by opposing deviations from normal blood pressure

Question 778: All of the following increase blood pressure except:

A. Angiotensin II
B. Sympathetic activation
C. Atrial natriuretic peptide (Correct Answer)
D. Aldosterone

Explanation: ***Atrial natriuretic peptide*** - **Atrial natriuretic peptide (ANP)** is released by atrial cells in response to increased atrial stretch (due to higher blood volume/pressure). - Its primary function is to **decrease blood pressure** by promoting natriuresis (sodium excretion) and diuresis (water excretion), leading to reduced blood volume and vasodilation. *Angiotensin II* - **Angiotensin II** is a potent **vasoconstrictor**, directly increasing systemic vascular resistance and thereby blood pressure. - It also stimulates the release of **aldosterone**, which leads to increased sodium and water reabsorption, further elevating blood volume and blood pressure. *Sympathetic activation* - **Sympathetic activation** releases catecholamines (norepinephrine and epinephrine), which bind to alpha-1 adrenergic receptors on vascular smooth muscle, causing **vasoconstriction**. - It also increases **heart rate** and myocardial contractility, leading to an increased cardiac output, all contributing to elevated blood pressure. *Aldosterone* - **Aldosterone** is a mineralocorticoid hormone that promotes the reabsorption of **sodium and water** in the renal tubules. - This increases the **extracellular fluid volume** and subsequently the blood volume, which directly contributes to an increase in blood pressure.

Question 779: Which part of the action potential in cardiac pacemaker cells is primarily affected by calcium channel blockers?

A. Phase 1
B. Phase 2
C. Phase 3
D. Phase 0 (Correct Answer)

Explanation: ***Phase 0*** - In cardiac pacemaker cells (SA and AV nodes), **Phase 0 (rapid depolarization)** is mediated by **L-type calcium channels**, NOT the fast sodium channels seen in ventricular myocytes. - Calcium channel blockers primarily inhibit these **L-type calcium channels**, leading to a **slower rate of depolarization** and **reduced conduction velocity** through the AV node. - This is the **primary mechanism** by which these drugs slow heart rate and cause AV nodal blockade. *Phase 1* - Phase 1 (initial rapid repolarization) is **absent in pacemaker cells** because they lack the fast sodium channels and transient outward potassium currents characteristic of ventricular myocytes. - This phase is not relevant to pacemaker cell action potentials. *Phase 2* - Phase 2 (plateau phase) is also **absent or minimal in pacemaker cells**. - Pacemaker action potentials lack the prolonged plateau seen in ventricular myocytes. - This phase is not the primary target of calcium channel blockers in pacemaker tissue. *Phase 3* - Phase 3 (repolarization) occurs in pacemaker cells and is mediated by **potassium efflux**. - Calcium channel blockers do **not directly affect** this phase, as it is driven by potassium channels, not calcium channels. - Their effect on Phase 3 is minimal compared to their direct action on Phase 0.

Question 780: Which of the following statements about cardiac muscle is incorrect?

A. Cardiac muscle has a short refractory period. (Correct Answer)
B. Cardiac muscle obeys the all or none law.
C. Cardiac muscle exhibits the Frank-Starling mechanism
D. Cardiac muscle has automaticity and rhythmicity

Explanation: ***Cardiac muscle has a short refractory period.*** - This statement is **incorrect** because cardiac muscle has a **long refractory period** (~250 ms), which prevents summation and tetanus by ensuring that the muscle relaxes completely before another action potential can be initiated. - The long refractory period is crucial for maintaining the heart's **pumping efficiency** and preventing arrhythmias. *Cardiac muscle obeys the all or none law.* - This statement is **correct**. Individual **cardiac muscle cells** obey the **all-or-none law**; when a stimulus reaches threshold, the cell contracts fully. - The heart as a whole organ can grade its contraction force through recruitment of more fibers and the Frank-Starling mechanism, but at the cellular level, the all-or-none principle applies. *Cardiac muscle exhibits the Frank-Starling mechanism* - This statement is **correct**. The **Frank-Starling mechanism** describes the heart's ability to increase its force of contraction and stroke volume in response to an increase in **venous return** or end-diastolic volume. - This intrinsic regulatory mechanism allows the heart to match its output to the venous return, optimizing cardiac efficiency. *Cardiac muscle has automaticity and rhythmicity* - This statement is **correct**. **Automaticity** refers to the ability of specialized cardiac cells (e.g., in the sinoatrial node) to spontaneously generate action potentials without external nervous stimulation. - **Rhythmicity** is the regular, cyclical discharge of these action potentials, which drives the rhythmic beating of the heart.

Practice by Chapter

Cardiac Electrophysiology

Practice Questions

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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