Cardiovascular System Practice Questions

Q: Which of the following acts as a local vasodilator?

Carbon dioxide tension. **Explanation:** Local blood flow is primarily regulated by metabolic autoregulation. When tissues become metabolically active, they consume nutrients and produce metabolic byproducts that act as local vasodilators to increase blood flow and meet the increased demand. **Why Carbon Dioxide (CO₂) Tension is correct:** Increased CO₂ tension ($PCO_2$) is a potent local vasodilator, particularly in the cerebral and skeletal muscle circulation. As metabolic activity increases, CO₂ levels rise. This leads to a decrease in local pH (acidosis) and directly relaxes vascular smooth muscle cells, causing vasodilation to "wash out" the metabolic waste. **Analysis of Incorrect Options:** * **Oxygen Tension ($PO_2$):** High oxygen tension acts as a **vasoconstrictor** in most systemic tissues. Conversely, it is *low* oxygen tension (hypoxia) that acts as a vasodilator (except in the pulmonary circulation, where hypoxia causes vasoconstriction). * **pH:** A high pH (alkalosis) generally acts as a vasoconstrictor. It is a **low pH** (acidosis), often resulting from lactic acid or CO₂ accumulation, that functions as a local vasodilator. * **Option D:** This is a duplicate of the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Most Potent Cerebral Vasodilator:** CO₂ tension is the most important factor regulating cerebral blood flow. Hyperventilation (which lowers $PCO_2$) is used clinically to cause cerebral vasoconstriction and reduce intracranial pressure. * **Other Local Vasodilators:** Adenosine (crucial in coronary circulation), $K^+$ ions, $H^+$ ions, Lactic acid, and Nitric Oxide (NO). * **The Pulmonary Exception:** While hypoxia causes vasodilation systemically, it causes **vasoconstriction** in the lungs (Hypoxic Pulmonary Vasoconstriction) to shunt blood away from poorly ventilated alveoli.

Q: What is true about fetal circulation?

The heart receives blood with high oxygen saturation.. ### Explanation **Correct Answer: D. The heart receives blood with high oxygen saturation.** In fetal circulation, the oxygenated blood from the placenta travels via the **umbilical vein** to the **Ductus Venosus**, bypassing the liver to enter the Inferior Vena Cava (IVC). Upon reaching the right atrium, a physiological mechanism called **"streaming"** occurs. The "crista dividens" (the lower edge of the septum secundum) directs this highly oxygenated IVC blood through the **Foramen Ovale** into the left atrium. From there, it enters the left ventricle and is pumped into the ascending aorta. Consequently, the **coronary arteries** and the **carotid arteries** (supplying the heart and brain) receive the most oxygenated blood available in the fetus (approx. 65-70% saturation). **Why other options are incorrect:** * **A:** Blood in the **SVC** is deoxygenated blood returning from the upper body (saturation ~40%), whereas the IVC carries oxygenated blood from the placenta. * **B:** In the fetus, the **Right Ventricular pressure is higher** than the Left Ventricular pressure. This is due to high pulmonary vascular resistance (collapsed lungs) and low systemic resistance (placenta). * **C:** The brain receives blood from the ascending aorta (via the brachiocephalic, carotid, and subclavian arteries), which is **highly oxygenated** due to the streaming effect mentioned above. **High-Yield NEET-PG Pearls:** 1. **Highest $PO_2$:** Found in the **Umbilical Vein** (approx. 30-35 mmHg; 80% saturation). 2. **Lowest $PO_2$:** Found in the **Umbilical Arteries** (returning to the placenta). 3. **Ductus Arteriosus:** Shunts deoxygenated blood from the pulmonary artery to the descending aorta (distal to the branching of head/neck vessels) to protect the lungs from fluid overload. 4. **Closure:** The Foramen Ovale closes functionally at birth due to increased left atrial pressure.

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: Total cutaneous blood flow is

450 ml/min. **Explanation:** The total cutaneous blood flow in a resting adult at a comfortable ambient temperature is approximately **450 ml/min**, which accounts for about **8-10% of the total cardiac output**. The primary function of cutaneous circulation is **thermoregulation** rather than metabolic demand. The skin contains specialized **arteriovenous (AV) anastomoses**, particularly in the fingertips, palms, and earlobes. These shunts are under heavy sympathetic control; when body temperature rises, sympathetic tone decreases, allowing blood to bypass capillary beds and flow into venous plexuses to facilitate heat loss. **Analysis of Options:** * **A (1500 ml/min):** This represents the approximate blood flow to the **Liver** (the organ receiving the highest percentage of cardiac output, ~25-30%). * **B (1000-1200 ml/min):** This is the typical **Renal blood flow**, representing about 20-25% of cardiac output. * **D (250 ml/min):** This is the approximate **Coronary blood flow** at rest (about 4-5% of cardiac output). **High-Yield Clinical Pearls for NEET-PG:** * **Triple Response of Lewis:** A physiological reaction to skin injury consisting of Red reaction (capillary dilatation), Flare (arteriolar dilatation via axon reflex), and Wheal (exudation due to increased permeability). * **Maximum Flow:** Under extreme heat stress, cutaneous blood flow can increase significantly to as much as **7-8 L/min** to dissipate heat. * **Control:** Cutaneous vessels are primarily regulated by the **Sympathetic Nervous System** (norepinephrine) and local factors; they lack significant autoregulation compared to the brain or heart.

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: Which of the following is NOT a red blood cell membrane protein?

Nebulin. The red blood cell (RBC) membrane is a complex structure composed of a lipid bilayer supported by a specialized protein cytoskeleton that provides the cell with its characteristic biconcave shape and remarkable deformability. **Why Nebulin is the correct answer:** **Nebulin** is a giant protein found exclusively in **skeletal muscle**. It acts as a "molecular ruler" that regulates the length of thin (actin) filaments within the sarcomere. It is not found in the RBC membrane. **Explanation of incorrect options:** * **Spectrin (Option C):** This is the most abundant peripheral membrane protein in RBCs. It forms a flexible hexagonal meshwork that maintains the structural integrity of the cell. * **Ankyrin (Option A):** This is a key "linker" protein. It anchors the spectrin cytoskeleton to the integral membrane protein, Band 3, ensuring the membrane stays attached to the cytoskeleton. * **Glycophorin (Option D):** This is an integral membrane protein. It is rich in sialic acid, which gives the RBC surface a negative charge (zeta potential), preventing cells from sticking to each other and the vessel walls. **High-Yield Clinical Pearls for NEET-PG:** 1. **Hereditary Spherocytosis:** Most commonly caused by a deficiency in **Ankyrin** (most common) or **Spectrin**. This leads to a loss of membrane surface area, resulting in spherical, fragile RBCs. 2. **Hereditary Elliptocytosis:** Primarily caused by defects in **Spectrin** or **Protein 4.1**. 3. **Band 3:** This is the major integral protein that functions as a chloride-bicarbonate exchanger (essential for the Bohr effect and CO2 transport).

Question 1

Which of the following acts as a local vasodilator?

Accepted Answer

Carbon dioxide tension

Answer

Oxygen tension

Answer

pH

Question 2

What is true about fetal circulation?

Accepted Answer

The heart receives blood with high oxygen saturation.

Answer

Blood in the superior vena cava (SVC) has more oxygen saturation.

Answer

Pressure in the left ventricle is higher than in the right ventricle.

Answer

The brain receives blood with low oxygen saturation.

Question 3

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 4

Total cutaneous blood flow is

Accepted Answer

450 ml/min

Answer

1500 ml/min

Answer

1000 ml/min

Answer

250 ml/min

Question 5

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 6

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 7

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 8

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 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

Which of the following is NOT a red blood cell membrane protein?

Accepted Answer

Nebulin

Answer

Ankyrin

Answer

Spectrin

Answer

Glycophorin

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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