Cardiovascular System Practice Questions

Q: What is the second messenger involved in vagal bradycardia?

cAMP. **Explanation:** The correct answer is **A. cAMP**. Vagal bradycardia is mediated by the parasympathetic nervous system via the **Vagus nerve (CN X)**. The postganglionic parasympathetic fibers release **Acetylcholine (ACh)**, which binds to **Muscarinic M2 receptors** located on the SA and AV nodes. The M2 receptor is a G-protein coupled receptor (GPCR) linked to an **inhibitory G-protein (Gi)**. Activation of Gi leads to the **inhibition of Adenylyl Cyclase**, which results in a **decrease in intracellular cyclic AMP (cAMP)** levels. This reduction in cAMP leads to: 1. Decreased opening of HCN channels (funny current, $I_f$), slowing the rate of spontaneous depolarization. 2. Decreased activation of Protein Kinase A (PKA), leading to reduced $Ca^{2+}$ influx. Additionally, the Gβγ subunit directly opens **K+ channels ($I_{K-ACh}$)**, causing hyperpolarization. **Why other options are incorrect:** * **B & C (Ca2+ and DAG):** These are second messengers associated with the **Gq pathway** (e.g., M1, M3, M5 receptors or Alpha-1 receptors). While calcium influx is ultimately reduced in bradycardia, it is a downstream effect of decreased cAMP, not the primary second messenger of the M2 pathway. * **D (None of the above):** Incorrect, as the cAMP pathway is the well-established mechanism for M2 receptor signaling. **High-Yield Clinical Pearls for NEET-PG:** * **M2 Receptors:** Primarily in the heart (Atria > Ventricles). * **M3 Receptors:** Primarily in smooth muscles and glands (linked to Gq/IP3-DAG). * **Atropine:** A muscarinic antagonist used to treat symptomatic bradycardia by blocking these M2 receptors. * **Vagal Escape:** If vagal stimulation is prolonged, the ventricles may begin to beat at their own intrinsic rhythm (Purkinje fiber pace).

Q: In the cardiac cycle diagram, when does the first heart sound occur?

Point A. ***Point A*** - The first heart sound (**S1**) occurs at the beginning of **ventricular systole** when the **mitral and tricuspid valves** close abruptly. - This valve closure prevents **backflow of blood** from the ventricles to the atria as ventricular pressure rises. *Point B* - Typically represents the **aortic valve opening** during ventricular systole, which is silent. - This occurs after S1 when **ventricular pressure** exceeds **aortic pressure**. *Point C* - Usually indicates the second heart sound (**S2**) caused by **aortic and pulmonary valve** closure. - This marks the end of ventricular systole and beginning of **diastole**. *Point D* - Often represents the **dicrotic notch** or events during **ventricular diastole**. - This occurs after S2 during the **filling phase** of the cardiac cycle.

Q: Which of the following conditions does not cause right axis deviation in ECG?

Lying down posture. **Explanation:** The electrical axis of the heart represents the average direction of depolarization. **Right Axis Deviation (RAD)** is defined as a QRS axis between +90° and +180°. **Why "Lying down posture" is the correct answer:** When a person moves from a standing to a **lying down (supine)** position, the abdominal viscera push the diaphragm upward. This physically shifts the heart into a more horizontal position, leading to a **Left Axis Deviation (LAD)**, not RAD. Conversely, standing causes the heart to become more vertical, leading to a rightward shift. **Analysis of Incorrect Options:** * **End of deep inspiration:** During deep inspiration, the diaphragm descends. This makes the heart more vertical (verticalization), causing the electrical axis to shift to the **right**. * **Right Ventricular Hypertrophy (RVH):** This is a classic cause of RAD. The increased muscle mass in the right ventricle generates greater electrical forces, pulling the mean QRS vector toward the right side. * **Right Bundle Branch Block (RBBB):** In RBBB, depolarization of the right ventricle is delayed. This late electrical activity occurs directed toward the right, resulting in a rightward shift of the mean axis. **High-Yield Clinical Pearls for NEET-PG:** * **Normal Axis:** -30° to +90°. * **RAD Causes:** Thin tall build, RVH, RBBB, Left Posterior Fascicular Block (LPFB), Pulmonary Embolism (S1Q3T3 pattern), and Lateral Wall MI. * **LAD Causes:** Obesity, Pregnancy, Ascites (all via diaphragm elevation), LVH, LBBB, and Left Anterior Fascicular Block (LAFB). * **Quick Rule:** If QRS is positive in Lead I and negative in aVF, it is LAD. If QRS is negative in Lead I and positive in aVF, it is RAD.

Q: Edema occurs when plasma protein level falls below which value?

5 g/dL. **Explanation:** The formation of edema is governed by **Starling’s Forces**, which regulate fluid exchange between capillaries and the interstitium. The two primary forces are capillary hydrostatic pressure (pushing fluid out) and **plasma colloid osmotic pressure (COP)** (pulling fluid in). **Plasma proteins**, specifically albumin, are the primary determinants of COP. Normal total plasma protein levels range from **6.4 to 8.3 g/dL**. When these levels drop significantly (hypoproteinemia), the COP decreases, allowing fluid to leak into the interstitial space, resulting in edema. Clinically, edema typically manifests when: 1. **Total plasma protein** levels fall below **5 g/dL**. 2. **Albumin** levels fall below **2.5 g/dL**. **Analysis of Options:** * **Option A (8 g/dL):** This is within the normal physiological range; no edema occurs. * **Option B (2 g/dL):** While edema is definitely present at this level, it is a severe state. The threshold for the *onset* of edema is higher (5 g/dL). * **Option C (5 g/dL):** **Correct.** This is the critical threshold where the oncotic pressure can no longer counteract hydrostatic pressure. * **Option D (10 g/dL):** This represents hyperproteinemia (e.g., in Multiple Myeloma), which would actually increase COP and prevent edema. **High-Yield NEET-PG Pearls:** * **Albumin** contributes to about 75–80% of the total plasma COP because of its high concentration and low molecular weight. * Common causes of hypoproteinemic edema include **Nephrotic syndrome** (protein loss), **Cirrhosis** (decreased synthesis), and **Kwashiorkor** (malnutrition). * **Myxedema** (Hypothyroidism) is a "non-pitting" edema caused by the accumulation of mucopolysaccharides, not a drop in plasma proteins.

Q: Blood flow to the brain is not influenced by which of the following?

PaO2. **Explanation:** The cerebral circulation is unique in its autoregulatory mechanisms, designed to maintain constant blood flow despite fluctuations in systemic pressure. **Why PaO2 is the correct answer:** Under normal physiological conditions, **PaO2 has little to no effect** on cerebral blood flow (CBF). CBF remains constant until PaO2 drops below a critical threshold of approximately **50 mmHg** (severe hypoxia). Only below this level does vasodilation occur to increase flow. Since the question implies normal physiological ranges, PaO2 is the least influential factor compared to the others. **Analysis of Incorrect Options:** * **PaCO2:** This is the **most potent physiological regulator** of CBF. An increase in PaCO2 (hypercapnia) causes marked cerebral vasodilation, while a decrease (hypocapnia) causes vasoconstriction. * **Cerebral Circulation:** Local factors such as metabolic products (H+, Adenosine, K+) and myogenic mechanisms directly control the resistance of cerebral vessels to maintain flow. * **Systemic Circulation:** While the brain autoregulates between a Mean Arterial Pressure (MAP) of **60–140 mmHg**, extreme changes in systemic circulation (e.g., shock or hypertensive crisis) will directly impact cerebral perfusion pressure (CPP = MAP - ICP). **High-Yield Pearls for NEET-PG:** 1. **CO2 Reactivity:** For every 1 mmHg rise in PaCO2, CBF increases by approximately 3-4%. 2. **Hyperventilation:** Clinically used in neurosurgery to lower PaCO2, causing vasoconstriction to reduce intracranial pressure (ICP). 3. **Monro-Kellie Doctrine:** The cranial vault is a fixed volume; an increase in blood, CSF, or brain tissue must be compensated by a decrease in the others to maintain pressure.

Q: Under normal conditions, the SA node acts as the pacemaker due to which of the following?

Slow depolarization, early repolarization. **Explanation:** The SA node is the physiological pacemaker of the heart because it possesses the highest intrinsic rate of firing (automaticity). This is primarily due to the unique characteristics of its action potential. **1. Why Option C is Correct:** The SA node exhibits **slow depolarization** (Phase 4), also known as the pacemaker potential. This is mediated by the "funny" sodium currents ($I_f$) and T-type calcium channels. This gradual rise toward the threshold ensures a rhythmic, spontaneous discharge. Furthermore, the SA node undergoes **early repolarization** (Phase 3) compared to other parts of the conduction system. Because it completes its recovery cycle faster than the AV node or Purkinje fibers, it reaches the threshold for the next beat first, thereby "overdrive suppressing" other potential pacemakers and maintaining control of the heart rate. **2. Why Other Options are Incorrect:** * **Options B & D (Rapid Depolarization):** Rapid depolarization (Phase 0) is a feature of **ventricular myocytes** and Purkinje fibers, mediated by fast sodium channels. The SA node lacks these channels and relies on slow L-type calcium channels for depolarization. * **Option A (Slow Repolarization):** If repolarization were slow, the refractory period would be prolonged, leading to a slower heart rate. The SA node must repolarize efficiently to initiate the next spontaneous depolarization cycle. **High-Yield NEET-PG Pearls:** * **Overdrive Suppression:** The mechanism by which the SA node inhibits slower latent pacemakers. * **Pre-potential (Phase 4):** The most critical phase for determining heart rate. Parasympathetic stimulation (ACh) decreases the slope of Phase 4, while Sympathetic stimulation (NE) increases it. * **Ionic Basis:** Phase 0 (Ca²⁺ influx), Phase 3 (K⁺ efflux), Phase 4 (Na⁺ influx via $I_f$ channels).

Q: A capillary that connects a metaeriole directly with a venule is called as?

Thoroughfare vessel. ### Explanation **1. Why the Correct Answer is Right:** The microcirculation consists of arterioles, capillaries, and venules. Within this network, a **metarteriole** acts as a transitional vessel. A **thoroughfare vessel** (or thoroughfare channel) is the distal continuation of a metarteriole that bypasses the true capillary bed and connects directly to a post-capillary venule. * **Mechanism:** When precapillary sphincters are constricted, blood is diverted away from the exchange network and flows directly through this "central channel" (metarteriole + thoroughfare vessel) to the venous side. This allows for rapid transit of blood without significant nutrient exchange. **2. Why the Other Options are Incorrect:** * **A. Windkessel vessel:** These are large elastic arteries (e.g., Aorta). They convert the intermittent, pulsatile output of the heart into a continuous flow through their elastic recoil properties. * **B. Resistance vessel:** These are primarily the **arterioles**. They have thick muscular walls and provide the greatest resistance to blood flow, thereby regulating systemic blood pressure. * **C. Exchange vessel:** These are the **true capillaries**. They lack smooth muscle and consist of a single layer of endothelial cells, specialized for the diffusion of gases, nutrients, and waste. **3. High-Yield Clinical Pearls for NEET-PG:** * **Capacitance Vessels:** Veins and venules (they hold ~60-70% of total blood volume). * **Precapillary Sphincters:** These are not found on thoroughfare vessels; they are located only at the origin of **true capillaries**. Their activity is primarily regulated by local metabolites (e.g., low $O_2$, high $CO_2$, low pH). * **Flow Regulation:** Blood flow through the metarteriole-thoroughfare channel is "vasomotion" (intermittent flow), which is a key physiological concept in tissue perfusion.

Q: A 43-year-old woman is diagnosed with mitral valve stenosis. During physical examination, the first heart sound is abnormally loud. Which of the following heart valves are responsible for the production of the first heart sound?

Tricuspid and mitral. The first heart sound (**S1**) is produced by the closure of the **Atrioventricular (AV) valves**, which include the **Mitral (M1)** and **Tricuspid (T1)** valves [1]. This occurs at the beginning of ventricular systole when the intraventricular pressure exceeds the atrial pressure, forcing the valves shut to prevent backflow. * **Mitral Valve (M1):** Closes slightly before the tricuspid valve due to earlier left ventricular contraction [1]. * **Tricuspid Valve (T1):** Closes immediately after the mitral component. **Analysis of Options:** * **Option C (Correct):** Correctly identifies the two AV valves responsible for S1. * **Options A, B, and D (Incorrect):** These include the **Aortic** or **Pulmonary** valves. These are Semilunar valves, and their closure marks the beginning of diastole, producing the **second heart sound (S2)** [2]. **Clinical Correlation (Mitral Stenosis):** In the provided clinical scenario, the "loud S1" is a classic finding in **Mitral Stenosis**. This occurs because the thickened, stenotic leaflets remain wide open at the end of diastole; when systole begins, they shut with greater force and excursion, creating a "tapping" or loud S1. **High-Yield NEET-PG Pearls:** 1. **S1** is best heard at the **Apex** (Mitral area). 2. **S2** is best heard at the **Base** (2nd intercostal space). 3. **Loud S1:** Seen in Mitral Stenosis, Tachycardia, and short PR intervals. 4. **Soft S1:** Seen in Mitral Regurgitation, Heart Failure, and long PR intervals (1st-degree heart block). 5. **Splitting of S1:** Usually narrow and physiological; a wide split may indicate a Right Bundle Branch Block (RBBB).

Question 1

What is the second messenger involved in vagal bradycardia?

Accepted Answer

cAMP

Answer

Ca2+

Answer

DAG

Answer

None of the above

Question 2

In the cardiac cycle diagram, when does the first heart sound occur?

Accepted Answer

Point A

Answer

Point B

Answer

Point C

Answer

Point D

Question 3

Which of the following conditions does not cause right axis deviation in ECG?

Accepted Answer

Lying down posture

Answer

End of deep inspiration

Answer

Right ventricular hypertrophy

Answer

Right bundle branch block

Question 4

Edema occurs when plasma protein level falls below which value?

Accepted Answer

5 g/dL

Answer

8 g/dL

Answer

2 g/dL

Answer

10 g/dL

Question 5

Blood flow to the brain is not influenced by which of the following?

Accepted Answer

PaO2

Answer

PaCO2

Answer

Cerebral circulation

Answer

Systemic circulation

Question 6

Under normal conditions, the SA node acts as the pacemaker due to which of the following?

Accepted Answer

Slow depolarization, early repolarization

Answer

Slow depolarization, slow repolarization

Answer

Rapid depolarization, rapid repolarization

Answer

Rapid depolarization, delayed repolarization

Question 7

A capillary that connects a metaeriole directly with a venule is called as?

Accepted Answer

Thoroughfare vessel

Answer

Windkessel vessel

Answer

Resistance vessel

Answer

Exchange vessel

Question 8

Which of the following is a better predictor of vagal tone?

Accepted Answer

Basal heart rate

Answer

Ejection fraction

Answer

Stroke volume

Answer

LVET

Question 9

A 43-year-old woman is diagnosed with mitral valve stenosis. During physical examination, the first heart sound is abnormally loud. Which of the following heart valves are responsible for the production of the first heart sound?

Accepted Answer

Tricuspid and mitral

Answer

Aortic and mitral

Answer

Aortic and tricuspid

Answer

Mitral and pulmonary

Question 10

In the presence of a drug that blocks all effects of norepinephrine and epinephrine on the heart, the autonomic nervous system can:

Accepted Answer

Lower the heart rate below its intrinsic rate

Answer

Raise the heart rate above its intrinsic rate

Answer

Raise and lower the heart rate above and below its intrinsic rate

Answer

Neither raise nor lower the heart rate from its intrinsic rate

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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