Cardiovascular System Practice Questions

Q: Which of these changes in fetal circulation happen immediately at birth?

Functional closure of ductus arteriosus. **Explanation:** The transition from fetal to neonatal circulation involves immediate physiological changes and gradual anatomical changes. **Why Option C is Correct:** The **functional closure of the ductus arteriosus** occurs almost **immediately (within 10–15 hours)** after birth. This is triggered by two main factors: 1. **Increased Oxygen Tension:** As the baby takes its first breath, systemic $PaO_2$ rises, causing contraction of the smooth muscles in the ductus wall. 2. **Fall in Prostaglandin ($PGE_2$) levels:** The removal of the placenta (the primary source of $PGE_2$) and increased metabolism in the lungs lead to ductal constriction. **Why Other Options are Incorrect:** * **A & D (Obliteration of Ductus Venosus and Distal Hypogastric Arteries):** While these vessels cease to function shortly after the cord is clamped, their **obliteration** (anatomical closure) is a gradual process taking several days to weeks. * **B (Formation of Ligamentum Teres):** This is the end-stage anatomical result of the obliterated left umbilical vein. Anatomical closure of fetal remnants typically takes **2–3 months** to complete. **High-Yield NEET-PG Pearls:** * **Functional vs. Anatomical:** Functional closure (physiological) happens in hours; Anatomical closure (fibrosis) takes weeks. * **Remnants Summary:** * **Ductus Arteriosus** $\rightarrow$ Ligamentum arteriosum * **Ductus Venosus** $\rightarrow$ Ligamentum venosum * **Left Umbilical Vein** $\rightarrow$ Ligamentum teres hepatis * **Umbilical Arteries** $\rightarrow$ Medial umbilical ligaments * **Foramen Ovale** $\rightarrow$ Fossa ovalis (Functional closure is immediate due to increased left atrial pressure). * **Pharmacology:** **Indomethacin** (NSAID) is used to close a Patent Ductus Arteriosus (PDA), while **Alprostadil** ($PGE_1$) is used to keep it open in cyanotic heart diseases.

Q: A 40-year-old man presents with a resting heart rate of 180 beats/min. A pressure-volume diagram of the left ventricle is shown below. What is the cardiac output?

5.6 L/min. ***5.6 L/min*** - **Cardiac output** = **Stroke Volume** × **Heart Rate**; from the PV loop, **stroke volume** ≈ 31 mL (EDV - ESV), so CO = 31 mL × 180 bpm = 5,580 mL/min ≈ **5.6 L/min**. - The **width of the PV loop** represents stroke volume, which appears reduced due to **tachycardia** limiting ventricular filling time. *5.2 L/min* - This would correspond to a **stroke volume** of approximately 29 mL (5,200 ÷ 180), which is lower than what the PV loop demonstrates. - The calculation underestimates the actual **stroke volume** visible in the pressure-volume diagram. *4.8 L/min* - This represents a **stroke volume** of approximately 27 mL (4,800 ÷ 180), significantly lower than the loop shows. - This would indicate **severe cardiac dysfunction** with markedly reduced contractility, not consistent with the PV loop morphology. *6 L/min* - This would require a **stroke volume** of approximately 33 mL (6,000 ÷ 180), which is higher than what the PV loop indicates. - The calculation overestimates the **end-diastolic volume minus end-systolic volume** difference shown in the diagram.

Q: Which one of the following neurotransmitters functions to increase cardiac output?

Norepinephrine. **Explanation:** **Norepinephrine (Option C)** is the correct answer because it is the primary neurotransmitter of the postganglionic sympathetic nervous system. It increases cardiac output through its action on **$\beta_1$-adrenergic receptors** located in the myocardium and the sinoatrial (SA) node. This binding triggers a G-protein-mediated increase in cAMP, leading to: 1. **Positive Inotropy:** Increased force of contraction. 2. **Positive Chronotropy:** Increased heart rate. Since Cardiac Output (CO) = Stroke Volume (SV) × Heart Rate (HR), both mechanisms contribute to a significant rise in CO. **Analysis of Incorrect Options:** * **GABA (Option A):** The primary inhibitory neurotransmitter in the CNS. While it can influence central blood pressure regulation, it does not have a direct peripheral stimulatory effect on cardiac output. * **Serotonin (Option B):** Primarily involved in mood regulation and platelet aggregation. While it has complex effects on the vasculature (vasoconstriction/dilation), it is not the physiological mediator for increasing cardiac output. * **Glutamate (Option D):** The major excitatory neurotransmitter in the CNS. It is involved in synaptic plasticity and memory but does not act directly on the heart to increase output. **High-Yield Clinical Pearls for NEET-PG:** * **Receptor Specificity:** While Norepinephrine acts on $\alpha_1$ and $\beta_1$ receptors, **Epinephrine** (from the adrenal medulla) acts on $\alpha_1, \beta_1,$ and $\beta_2$. * **Parasympathetic Control:** Acetylcholine (ACh) acts on **$M_2$ receptors** to decrease heart rate (negative chronotropy), thereby decreasing cardiac output. * **Bowditch Effect:** An increase in heart rate leads to an increase in the force of contraction due to the inability of Na+/K+ ATPase to keep up, leading to higher intracellular calcium.

Q: During exercise, what happens to blood flow to the brain?

Unaltered. **Explanation:** The correct answer is **Unaltered (C)**. **1. Why it is correct:** During exercise, there is a massive increase in total cardiac output to meet the metabolic demands of skeletal muscles. However, the brain requires a constant, steady supply of oxygen and glucose to maintain consciousness and neurological function. This is achieved through **Cerebral Autoregulation**. Despite fluctuations in systemic blood pressure and the redistribution of blood to muscles and skin, the cerebral blood flow (CBF) remains remarkably constant at approximately **750 mL/min (or 15% of resting cardiac output)**. While the *percentage* of total cardiac output directed to the brain decreases, the *absolute volume* of blood flow remains unchanged. **2. Why other options are incorrect:** * **A. Decreased:** The brain is a vital organ; any significant decrease in flow would lead to syncope (fainting). Autoregulation prevents this during the sympathetic surge of exercise. * **B. Increased:** While blood flow to the heart and skeletal muscles increases significantly, the rigid cranium and autoregulatory mechanisms (myogenic and metabolic) prevent hyperperfusion of the brain. * **D. Initially increased and then decreases:** There is no physiological basis for this biphasic response in a healthy individual during standard exercise. **3. NEET-PG High-Yield Pearls:** * **Most sensitive factor for CBF:** Arterial $PCO_2$. Hypercapnia causes vasodilation (increasing flow), while hypocapnia (hyperventilation) causes vasoconstriction. * **Autoregulation Range:** Cerebral blood flow remains constant between a Mean Arterial Pressure (MAP) of **60 to 140 mmHg**. * **Organ with the highest blood flow per 100g tissue:** Carotid bodies (followed by the Kidneys). * **Organ with the highest oxygen extraction ($A-V O_2$ difference):** The Heart.

Q: Which of the following causes vasoconstriction in all vascular beds?

TXA2. **Explanation** The correct answer is **TXA2 (Thromboxane A2)**. **Why TXA2 is correct:** Thromboxane A2 is a potent eicosanoid synthesized primarily by platelets via the cyclooxygenase (COX) pathway. Its primary physiological roles are **platelet aggregation** and **potent vasoconstriction**. Unlike other prostaglandins which may have varying effects depending on the tissue or receptor subtype, TXA2 acts via the TP receptor to cause generalized vasoconstriction across all vascular beds, including the renal, coronary, and pulmonary circulations. **Why the other options are incorrect:** * **PGE2 (Prostaglandin E2):** This is primarily a **vasodilator** in most vascular beds. While it can cause constriction in specific areas (like the ductus arteriosus or certain segments of the renal vasculature under specific conditions), it is generally known for its role in inflammatory vasodilation and maintaining the patency of the ductus arteriosus. * **PGF2α (Prostaglandin F2 alpha):** While PGF2α is a vasoconstrictor (especially in the pulmonary and uterine vessels), it is primarily known for its potent **smooth muscle contracting** effects on the uterus and bronchi. It does not exert a universal vasoconstrictive effect across all vascular beds as consistently as TXA2. * **PGI2 (Prostacyclin):** Produced by vascular endothelial cells, PGI2 is the functional antagonist to TXA2. It is a potent **vasodilator** and inhibitor of platelet aggregation. **High-Yield NEET-PG Pearls:** * **Aspirin's Mechanism:** Low-dose aspirin irreversibly inhibits COX-1, shifting the balance in favor of **PGI2 (vasodilator)** over **TXA2 (vasoconstrictor)**, which explains its cardioprotective effect. * **Vasoactive Mnemonic:** Remember **"I"** for **I**nhibition (PGI2 inhibits aggregation/constriction) and **"TX"** for **T**hrombus (TXA2 promotes thrombus/constriction). * **Ductus Arteriosus:** PGE2 keeps it open; NSAIDs (Indomethacin) close it by inhibiting PGE2 synthesis.

Q: Pacemaker potential occurs due to which of the following?

Opening of transient, rapid T-type Ca2+ channels. **Explanation:** The **Pacemaker Potential** (also known as the prepotential or Phase 4 depolarization) is the slow, spontaneous depolarization of the SA node that brings the membrane potential to the threshold, triggering an action potential. **1. Why Option A is Correct:** The pacemaker potential occurs in three sequential ionic steps: * **Initial Phase:** Triggered by the opening of **"Funny" Na+ channels ($I_f$)**, which allow sodium influx. * **Late Phase:** As the membrane depolarizes, **T-type (Transient) Ca2+ channels** open. These channels provide the final push (calcium influx) to reach the threshold potential (approx. -40 mV). * Once the threshold is reached, **L-type (Long-lasting) Ca2+ channels** open to cause the actual depolarization (Phase 0). Therefore, the opening of T-type channels is a critical component of the pacemaker potential. **2. Why Other Options are Incorrect:** * **Option B:** Opening of K+ channels causes **repolarization** (Phase 3), as K+ leaves the cell, making the interior more negative. * **Option C:** Closure of Ca2+ channels would stop depolarization; it is the *opening* of these channels that drives the potential toward the threshold. * **Option D:** The prepotential begins with the **opening** of funny Na+ channels, not their closure. **Clinical Pearls & High-Yield Facts:** * **SA Node:** The primary pacemaker because it has the steepest prepotential slope. * **Autonomic Influence:** Sympathetic stimulation increases the slope (faster heart rate), while Parasympathetic (Vagus) stimulation decreases the slope and hyperpolarizes the cell (slower heart rate). * **Ivabradine:** A clinical drug that selectively blocks the **$I_f$ (funny) channels**, used to reduce heart rate in angina and heart failure. * **Phase 0 in SA Node:** Unlike ventricular muscle (where Phase 0 is Na+ dependent), the SA node's Phase 0 is **Ca2+ dependent**.

Q: The shape of the arterial pulse is influenced by which of the following?

Arterial wall elasticity. **Explanation:** The shape and contour of the arterial pulse are primarily determined by the **elasticity of the arterial walls** (compliance) and the stroke volume. When the left ventricle ejects blood into the aorta, the energy is stored by the expansion of the elastic arterial walls (Potential Energy). During diastole, the elastic recoil (Windkessel effect) converts this into kinetic energy, maintaining continuous blood flow and shaping the pulse wave. A decrease in elasticity, such as in atherosclerosis, leads to a steeper rise and a higher pulse pressure. **Why other options are incorrect:** * **Viscosity of blood (A):** Viscosity primarily affects peripheral resistance and the *rate* of flow (Poiseuille’s Law) rather than the specific morphological shape of the pressure wave. * **Velocity of blood (B):** While velocity relates to flow, the pulse is a *pressure wave* that travels significantly faster (5–12 m/s) than the actual blood flow (0.5 m/s). Velocity does not dictate the contour of the wave. * **Cross-sectional area (D):** This determines the velocity of flow (Inversely proportional) but does not influence the characteristic dicrotic notch or the upstroke of the arterial pulse. **High-Yield Clinical Pearls for NEET-PG:** * **Anacrotic Notch:** Seen in the ascending limb in Aortic Stenosis. * **Dicrotic Notch:** Caused by the closure of the aortic valve; it marks the beginning of diastole. * **Pulsus Bisferiens:** A double-peaked pulse seen in AR + AS or Hypertrophic Obstructive Cardiomyopathy (HOCM). * **Windkessel Effect:** The process where elastic recoil of central arteries maintains diastolic pressure; loss of this effect causes isolated systolic hypertension in the elderly.

Q: Which of the following is NOT a component of the jugular venous pulse (JVP)?

The C wave is called the Dicrotic notch. The Jugular Venous Pulse (JVP) reflects pressure changes in the right atrium. Understanding its waveforms is crucial for NEET-PG. ### **Why Option B is Correct (The Incorrect Statement)** The **C wave** in the JVP is caused by the bulging of the tricuspid valve into the right atrium during early ventricular contraction (isovolumetric contraction). In contrast, the **Dicrotic notch** (incisura) is a feature of the **Arterial Pressure Waveform**, representing the closure of the aortic valve. These are two distinct physiological events in different systems. ### **Analysis of Other Options** * **Option A:** In a normal JVP, the **'a' wave** (atrial contraction) is the tallest wave, followed by the 'v' wave (venous filling). * **Option B (X-descent):** This occurs due to atrial relaxation and the downward pulling of the tricuspid annulus during **ventricular systole**. * **Option D (Y-descent):** This represents the rapid emptying of the right atrium into the right ventricle following the opening of the tricuspid valve during **ventricular diastole**. ### **High-Yield Clinical Pearls for NEET-PG** * **Giant 'a' waves:** Seen in Tricuspid Stenosis, Pulmonary Hypertension, and Pulmonary Stenosis. * **Cannon 'a' waves:** Seen in AV dissociation (Complete Heart Block) or Ventricular Tachycardia (atria contract against a closed tricuspid valve). * **Absent 'a' wave:** Pathognomonic for **Atrial Fibrillation**. * **Prominent 'v' wave:** Seen in Tricuspid Regurgitation (Lancisi’s sign). * **Friedreich’s Sign:** A steep 'y' descent seen in Constrictive Pericarditis.

Question 1

Which of these changes in fetal circulation happen immediately at birth?

Accepted Answer

Functional closure of ductus arteriosus

Answer

Obliteration of ductus venosus

Answer

Formation of ligamentum teres

Answer

Obliteration of distal hypogastric arteries

Question 2

A patient's ECG shows Lead III with no S wave, but normal P, R, and T waves. What conclusions can be drawn about the patient's cardiac status?

Accepted Answer

No indications of cardiac abnormalities.

Answer

Abnormal activation of parts of the base of the heart.

Answer

Abnormal activation of parts of the apex of the heart.

Answer

Cardiac depression.

Question 3

What period does ventricular contraction correspond to on an ECG?

Accepted Answer

Beginning of Q wave to the end of T wave

Answer

Beginning of Q wave to end of S wave

Answer

Beginning of P wave to end of T wave

Answer

Beginning of R wave to the end of T wave, if Q wave is absent

Question 4

A 40-year-old man presents with a resting heart rate of 180 beats/min. A pressure-volume diagram of the left ventricle is shown below. What is the cardiac output?

Accepted Answer

5.6 L/min

Answer

5.2 L/min

Answer

4.8 L/min

Answer

6 L/min

Question 5

Which one of the following neurotransmitters functions to increase cardiac output?

Accepted Answer

Norepinephrine

Answer

GABA

Answer

Serotonin

Answer

Glutamate

Question 6

During exercise, what happens to blood flow to the brain?

Accepted Answer

Unaltered

Answer

Decreased

Answer

Increased

Answer

Initially increased and then decreases

Question 7

Which of the following causes vasoconstriction in all vascular beds?

Accepted Answer

TXA2

Answer

PGE2

Answer

PGF2α

Answer

PGI2

Question 8

Pacemaker potential occurs due to which of the following?

Accepted Answer

Opening of transient, rapid T-type Ca2+ channels

Answer

Opening of K+ channels

Answer

Closure of Ca2+ channels

Answer

Closure of funny Na+ channels

Question 9

The shape of the arterial pulse is influenced by which of the following?

Accepted Answer

Arterial wall elasticity

Answer

Viscosity of blood

Answer

Velocity of blood

Answer

Cross-sectional area of the artery

Question 10

Which of the following is NOT a component of the jugular venous pulse (JVP)?

Accepted Answer

The C wave is called the Dicrotic notch

Answer

A wave is bigger than the V wave

Answer

The X wave is seen during ventricular systole

Answer

The Y descent is seen during ventricular diastole

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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