Cardiovascular System Practice Questions

Q: C wave in JVP is due to?

Tricuspid valve bulging into right atrium. The Jugular Venous Pulse (JVP) reflects pressure changes in the right atrium throughout the cardiac cycle. Understanding its waveforms is a high-yield topic for NEET-PG. ### **Explanation of the Correct Answer** The **'c' wave** occurs during **early ventricular systole**. As the right ventricle begins to contract, the intraventricular pressure rises sharply, causing the **tricuspid valve to bulge backward into the right atrium**. This sudden displacement of the valve increases right atrial pressure, creating the positive 'c' wave (c stands for *ventricular contraction* or *carotid* impulse). ### **Analysis of Incorrect Options** * **A. Atrial contraction:** This produces the **'a' wave**. It occurs at the end of diastole and is the first positive deflection. * **C. Right atrial filling:** This occurs while the tricuspid valve is closed during ventricular systole, leading to the **'v' wave**. * **D. Rapid ventricular filling:** This occurs during early diastole when the tricuspid valve opens. It corresponds to the **'y' descent** (the fall in atrial pressure as blood flows into the ventricle). ### **High-Yield Clinical Pearls for NEET-PG** * **Giant 'a' waves:** Seen in Tricuspid Stenosis, Pulmonary Hypertension, and Pulmonary Stenosis. * **Cannon 'a' waves:** Occur when the atrium contracts against a closed tricuspid valve (e.g., Complete Heart Block, Ventricular Tachycardia). * **Absent 'a' waves:** Pathognomonic for **Atrial Fibrillation**. * **Prominent 'v' waves:** Characteristic of **Tricuspid Regurgitation** (due to blood leaking back into the atrium during systole). * **Friedreich’s Sign:** A steep 'y' descent seen in Constrictive Pericarditis.

Q: Nitric oxide (NO) is primarily released by which of the following cell types?

Endothelial cells. **Explanation:** **Correct Answer: C. Endothelial cells** Nitric Oxide (NO), formerly known as **Endothelium-Derived Relaxing Factor (EDRF)**, is primarily synthesized in vascular endothelial cells. It is produced from the amino acid **L-arginine** by the action of the enzyme **endothelial Nitric Oxide Synthase (eNOS)**. Once released, NO diffuses into adjacent vascular smooth muscle cells, where it activates **soluble guanylyl cyclase**, increasing intracellular **cGMP**. This leads to smooth muscle relaxation and subsequent vasodilation, playing a critical role in regulating blood pressure and regional blood flow. **Analysis of Incorrect Options:** * **A & B (Neutrophils and Macrophages):** While these cells can produce NO via **inducible Nitric Oxide Synthase (iNOS)** during inflammatory responses to kill pathogens, they are not the *primary* physiological source of NO in the body. eNOS in the endothelium provides the basal, continuous release required for vascular homeostasis. * **D (Lymphocytes):** These cells are primarily involved in adaptive immunity (antibody production and cell-mediated immunity) and are not a significant source of Nitric Oxide. **High-Yield Clinical Pearls for NEET-PG:** * **Isoforms of NOS:** There are three types: **nNOS** (Neuronal/Type I), **iNOS** (Inducible/Type II - found in macrophages), and **eNOS** (Endothelial/Type III). * **Mechanism:** NO → ↑ cGMP → Protein Kinase G → Dephosphorylation of Myosin Light Chain → **Vasodilation**. * **Potent Stimuli:** Shear stress (blood flow) and Acetylcholine trigger NO release from the endothelium. * **Therapeutic Link:** Nitroglycerin acts by being converted into NO, providing rapid relief in Angina Pectoris.

Q: Rapid depolarization (phase 0) of the action potential of ventricular muscle results from the opening of which type of channels?

Voltage-gated Na+ channels. **Explanation:** The ventricular muscle action potential is a **"fast response"** action potential consisting of five distinct phases (0–4). **1. Why the Correct Answer is Right:** * **Phase 0 (Rapid Depolarization):** When the cell membrane reaches its threshold potential (approx. -70mV), **fast voltage-gated Na+ channels** open. This leads to a massive, rapid influx of sodium ions into the cell, causing the membrane potential to shoot up from -90mV to approximately +20 to +30mV. This phase is characterized by a high $dV/dt$ (slope), representing rapid conduction velocity. **2. Why the Incorrect Options are Wrong:** * **Option A (Voltage-gated Ca2+ channels):** These are responsible for the **Phase 2 (Plateau phase)** of the ventricular action potential. While they do cause depolarization in the SA/AV nodes (slow response potentials), they are not responsible for Phase 0 in ventricular muscle. * **Option C (ACh-activated K+ channels):** These are found primarily in the SA node and atria. Activation by the vagus nerve (parasympathetic) causes hyperpolarization and slows the heart rate; they do not contribute to ventricular depolarization. * **Option D (Inward rectifying K+ channels):** These channels (specifically $I_{K1}$) are primarily responsible for maintaining the **Resting Membrane Potential (Phase 4)** and contributing to late repolarization. **High-Yield Clinical Pearls for NEET-PG:** * **Class I Antiarrhythmics** (e.g., Lidocaine, Flecainide) work by blocking these Phase 0 voltage-gated Na+ channels. * **Tetrodotoxin (Pufferfish toxin)** specifically blocks these fast Na+ channels, inhibited Phase 0. * **Contrast with Pacemaker Cells:** In the SA node, Phase 0 is caused by **Ca2+ influx** (L-type channels), not Na+ influx. This is a frequent point of confusion in exams.

Q: A 50-year-old woman is brought to the emergency department unconscious following a motor vehicle accident. She is placed on telemetry to monitor her vitals continuously, and she remains hypotensive despite receiving a bolus of fluids and being placed on IV fluids. She regains consciousness and her pulse is 180/mm. Her ECG shows regularly spaced narrow, QRS complexes. No P wave is visible in most leads, but there is a small downward deflection immediately following QRS complexes in lead II. Carotid massage is performed, and her pulse is reduced to 80/min. Stimulation of the afferent fibres in which of the following nerves most likely resulted in the favourable response observed?

Glossopharyngeal nerve. **Explanation:** The clinical presentation describes a patient in **Supraventricular Tachycardia (SVT)**, specifically AV Nodal Reentrant Tachycardia (AVNRT), characterized by a rapid heart rate (180/min), narrow QRS complexes, and retrograde P waves (the "downward deflection" following the QRS). The successful resolution of the tachycardia via carotid massage is due to the **Baroreceptor Reflex**. 1. **Why Glossopharyngeal Nerve is Correct:** The **Carotid Sinus**, located at the bifurcation of the common carotid artery, contains baroreceptors sensitive to stretch. Carotid massage mimics high blood pressure, stimulating these receptors. The **afferent (sensory) limb** of this reflex is carried by the **Hering’s nerve**, which is a branch of the **Glossopharyngeal nerve (CN IX)**. These signals reach the nucleus tractus solitarius in the medulla, leading to increased parasympathetic (vagal) outflow and decreased sympathetic tone, which slows conduction through the AV node and terminates the SVT. 2. **Why Other Options are Incorrect:** * **Cardiac/Carotid Sympathetic Nerves:** These are involved in the efferent limb of sympathetic responses (increasing heart rate/contractility). Stimulating these would worsen tachycardia, not resolve it. * **Hypoglossal Nerve (CN XII):** This is a purely motor nerve responsible for tongue movements and has no role in the baroreceptor reflex arc. **High-Yield Pearls for NEET-PG:** * **Baroreceptor Reflex Arc:** Afferent = CN IX (Carotid sinus) & CN X (Aortic arch); Efferent = CN X (Parasympathetic) & Sympathetic chains. * **Vagal Maneuvers:** First-line treatment for stable SVT (Carotid massage, Valsalva). * **Drug of Choice for SVT:** Adenosine (6mg rapid IV bolus). * **Contraindication:** Never perform bilateral carotid massage simultaneously, as it can cause profound bradycardia or cerebral ischemia.

Q: Stimulation of the sympathetic nerves to the normal heart:

Decreases the duration of the QT interval. **Explanation:** Sympathetic stimulation of the heart is mediated by **Norepinephrine** acting on **$\beta_1$ receptors**. This results in positive chronotropy (increased heart rate) and positive dromotropy (increased conduction velocity). **Why Option C is Correct:** The **QT interval** represents the total time for ventricular depolarization and repolarization (ventricular systole). When the heart rate increases due to sympathetic stimulation, the cardiac cycle shortens. To maintain efficiency at high rates, the action potential duration must decrease. Sympathetic activity accelerates repolarization by increasing the activity of potassium channels (delayed rectifiers), thereby **shortening the QT interval**. **Analysis of Incorrect Options:** * **Option A:** The **TP interval** represents the period of ventricular diastole. As heart rate increases, the diastolic period (TP interval) is the most significantly **shortened** component of the cardiac cycle. * **Option B:** Sympathetic stimulation increases conduction velocity through the AV node (positive dromotropy). This results in a **shorter PR interval**, not a longer one. * **Option D:** In a normal heart, every P wave is followed by a QRS complex (1:1 conduction). Sympathetic stimulation does not cause AV block; rather, it enhances conduction. **NEET-PG High-Yield Pearls:** * **Bazett’s Formula:** Used to calculate the corrected QT ($QTc = QT / \sqrt{RR}$). It adjusts for the fact that QT interval naturally varies with heart rate. * **Vagal Stimulation:** Opposite to sympathetic effects, it decreases heart rate, prolongs the PR interval, and increases the TP interval. * **Propranolol:** A $\beta$-blocker that would increase the PR interval and potentially lengthen the QT interval by antagonizing sympathetic effects.

Question 1

C wave in JVP is due to?

Accepted Answer

Tricuspid valve bulging into right atrium

Answer

Atrial contraction

Answer

Right atrial filling

Answer

Rapid ventricular filling

Question 2

Nitric oxide (NO) is primarily released by which of the following cell types?

Accepted Answer

Endothelial cells

Answer

Neutrophils

Answer

Macrophages

Answer

Lymphocytes

Question 3

What are the characteristics of blood flow in capillaries?

Accepted Answer

Low velocity and high shear stress

Answer

High velocity, high stress

Answer

High velocity, low stress

Answer

Low velocity and pulsatile

Question 4

Venodilation in most tissues is primarily caused by which of the following factors?

Accepted Answer

Decreased oxygen tension

Answer

Decreased potassium concentration

Answer

Increased hydrogen ion concentration (acidosis)

Answer

Increased carbon dioxide concentration

Question 5

Rapid depolarization (phase 0) of the action potential of ventricular muscle results from the opening of which type of channels?

Accepted Answer

Voltage-gated Na+ channels

Answer

Voltage-gated Ca2+ channels

Answer

Acetylcholine-activated K+ channels

Answer

Inward rectifying K+ channels

Question 6

Coronary blood flow to the left ventricle increases during all of the following EXCEPT?

Accepted Answer

Early systole

Answer

Myocardial hypoxia

Answer

Stimulation of sympathetic nerves of the heart

Answer

Arterial hypertension

Question 7

Normally, the rate of the heart beat in a human is determined by:

Accepted Answer

The sinoatrial node

Answer

The bundle of His

Answer

All cardiac muscle

Answer

The cervical ganglion

Question 8

A 50-year-old woman is brought to the emergency department unconscious following a motor vehicle accident. She is placed on telemetry to monitor her vitals continuously, and she remains hypotensive despite receiving a bolus of fluids and being placed on IV fluids. She regains consciousness and her pulse is 180/mm. Her ECG shows regularly spaced narrow, QRS complexes. No P wave is visible in most leads, but there is a small downward deflection immediately following QRS complexes in lead II. Carotid massage is performed, and her pulse is reduced to 80/min. Stimulation of the afferent fibres in which of the following nerves most likely resulted in the favourable response observed?

Accepted Answer

Glossopharyngeal nerve

Answer

Cardiac sympathetic nerves

Answer

Carotid sympathetic nerves

Answer

Hypoglossal nerve

Question 9

Which of the following is NOT true about the sympathetic vasodilator system?

Accepted Answer

It has a strong basal tone.

Answer

It originates from the spinal cord.

Answer

The fibers to skeletal muscles are cholinergic.

Answer

After sympathectomy, the blood vessels dilate.

Question 10

Stimulation of the sympathetic nerves to the normal heart:

Accepted Answer

Decreases the duration of the QT interval

Answer

Increases the duration of the TP interval

Answer

Increases the duration of the PR interval

Answer

Leads to fewer P waves than QRS complexes

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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