Cardiovascular System Practice Questions

Q: Chemoreceptors operate between which pressure range?

40-100 mm Hg. **Explanation:** The peripheral chemoreceptors (located in the carotid and aortic bodies) are primarily sensitive to a decrease in $PO_2$, an increase in $PCO_2$, and a decrease in pH. However, they also play a crucial role in blood pressure regulation through the **Chemoreceptor Reflex**. **Why Option B is Correct:** The chemoreceptor reflex is not active under normal physiological blood pressure. It is considered an "emergency mechanism" that kicks in when the Mean Arterial Pressure (MAP) falls below the threshold of the baroreceptor reflex. Specifically, when blood pressure drops below **80–100 mm Hg**, blood flow to the chemoreceptor bodies decreases, leading to local hypoxia and hypercapnia within the receptors. This stimulates the vasomotor center to cause peripheral vasoconstriction, helping to raise blood pressure. The reflex is most potent and active between **40 and 100 mm Hg**. **Analysis of Incorrect Options:** * **Option A:** While chemoreceptors are active below 90 mm Hg, this range is too narrow. They remain functional and vital down to 40 mm Hg. * **Options C & D:** These ranges (70–150 and 70–220 mm Hg) are more characteristic of the **Baroreceptor Reflex**, which is the primary short-term regulator of blood pressure. Baroreceptors are most sensitive at a MAP of around 100 mm Hg and operate between 60 and 180 mm Hg. **High-Yield Clinical Pearls for NEET-PG:** * **Hierarchy of Reflexes:** Baroreceptors are the "First line of defense" (60–180 mm Hg), Chemoreceptors are the "Second line" (40–100 mm Hg), and the **CNS Ischemic Response** is the "Last ditch stand" (active below 60 mm Hg, most powerful below 20 mm Hg). * **Location:** Carotid bodies are located at the bifurcation of the common carotid artery (innervated by Hering’s nerve/CN IX); Aortic bodies are in the aortic arch (innervated by CN X). * **Key Stimulus:** The most potent stimulus for peripheral chemoreceptors is a **decrease in $PO_2$** (hypoxia).

Q: In a patient with a cardiac output of 5 liters/min and a body surface area of 1.7 square meters, what is the cardiac index?

3 L/min/sq. m. ### Explanation **1. Understanding the Correct Answer (A)** The **Cardiac Index (CI)** is a hemodynamic parameter that relates the Cardiac Output (CO) to a patient’s Body Surface Area (BSA). It is a more accurate clinical indicator than cardiac output alone because it accounts for the individual's body size. The formula for Cardiac Index is: $$\text{Cardiac Index (CI)} = \frac{\text{Cardiac Output (CO)}}{\text{Body Surface Area (BSA)}}$$ **Calculation:** * Given CO = 5 L/min * Given BSA = 1.7 m² * $CI = 5 / 1.7 \approx 2.94 \text{ L/min/m}^2$ Rounding to the nearest whole number, the answer is **3 L/min/m²**. **2. Analysis of Incorrect Options** * **Option B (4 L/min/m²):** This value is higher than the calculated result and represents a hyperdynamic state (e.g., sepsis or thyrotoxicosis). * **Option C (5 L/min/m²):** This incorrectly equates the Cardiac Output value with the Cardiac Index, ignoring the BSA correction. * **Option D (2.5 L/min/m²):** While this is within the lower limit of the normal physiological range, it does not match the mathematical calculation provided in the prompt. **3. Clinical Pearls & High-Yield Facts** * **Normal Range:** The normal Cardiac Index is typically **2.5 to 4.0 L/min/m²**. * **Clinical Significance:** A CI below **2.2 L/min/m²** is a diagnostic hallmark of **cardiogenic shock**. * **BSA Calculation:** In clinical practice, BSA is most commonly calculated using the **Mosteller formula** or the **DuBois formula**. * **NEET-PG Tip:** Remember that while CO changes with posture and exercise, the CI allows for a standardized comparison between a small child and a large adult.

Q: What is the autonomic supply to the SA node?

Sympathetic, excitatory. **Explanation:** The Sinoatrial (SA) node is the primary pacemaker of the heart, located in the right atrium. While it possesses intrinsic automaticity, its firing rate is modulated by the **Autonomic Nervous System (ANS)**. **1. Why Option B is Correct:** The SA node receives a rich supply of sympathetic fibers (primarily via the right stellate ganglion). Sympathetic stimulation releases **Norepinephrine**, which acts on **$\beta_1$ receptors**. This increases the slope of the prepotential (pacemaker potential) by increasing $I_f$ (funny current) and $I_{Ca}$ (calcium current), leading to a faster heart rate (**positive chronotropic effect**). Thus, the sympathetic supply is strictly **excitatory** to the heart's rate. **2. Why Other Options are Incorrect:** * **Option A:** While the parasympathetic system (via the Vagus nerve) does supply the SA node, its effect is **inhibitory** (slowing the heart rate). * **Options C & D:** These are incorrect because the ANS does not have a singular effect. The sympathetic system is excitatory, while the parasympathetic system is inhibitory. They work antagonistically to maintain cardiovascular homeostasis. **Clinical Pearls for NEET-PG:** * **Vagal Tone:** At rest, the heart is under dominant parasympathetic (vagal) influence. This is why the resting heart rate (~70 bpm) is lower than the intrinsic SA node rate (~100 bpm). * **Right vs. Left:** The **Right Vagus** nerve primarily supplies the **SA node** (affects rate), while the **Left Vagus** primarily supplies the **AV node** (affects conduction velocity). * **Neurotransmitters:** Sympathetic = Norepinephrine ($\beta_1$ receptors); Parasympathetic = Acetylcholine ($M_2$ receptors).

Q: Turbulence of blood flow increases when:

Diameter of blood vessel decreases. The concept of blood flow turbulence is governed by **Reynolds Number ($Re$)**, a dimensionless value used to predict whether flow is laminar or turbulent. The formula is: $$Re = \frac{\rho \cdot D \cdot v}{\eta}$$ *(Where $\rho$ = density, $D$ = diameter, $v$ = velocity, and $\eta$ = viscosity)* ### Why Option B is Correct While the formula suggests $Re$ is directly proportional to diameter ($D$), in the cardiovascular system, a **decrease in diameter** (like in stenosis) causes a disproportionate **increase in velocity ($v$)**. Because velocity increases to the fourth power relative to the radius change (Law of Continuity), the net effect is a significant rise in Reynolds Number. When $Re$ exceeds **2000–3000**, flow becomes turbulent. ### Why Other Options are Wrong * **A. Viscosity decreases:** According to the formula, viscosity ($\eta$) is in the denominator. A decrease in viscosity (e.g., severe anemia) actually **increases** the Reynolds Number and the likelihood of turbulence. * **C. Density decreases:** Density ($\rho$) is in the numerator. A decrease in density would **decrease** the Reynolds Number, making flow more laminar. * **D. Arteries are straight:** Turbulence is more likely to occur at **bends, branches, or bifurcations** (e.g., the carotid bulb). Straight vessels promote smooth, laminar flow. ### NEET-PG High-Yield Pearls * **Murmurs and Bruits:** Turbulence creates audible vibrations. In the heart, these are **murmurs**; in peripheral vessels (like a stenosed renal artery), they are **bruits**. * **Anemia & Turbulence:** In severe anemia, reduced RBC count decreases blood viscosity, leading to a "hyperdynamic state" and functional systolic murmurs. * **Critical Velocity:** The velocity at which laminar flow converts to turbulent flow is called critical velocity.

Q: What are the ECG changes seen in hypocalcemia?

Prolongation of ST segment. **Explanation:** The hallmark ECG finding in **hypocalcemia** is the **prolongation of the ST segment**, which leads to a prolonged **QT interval**. **1. Why the correct answer is right:** Calcium ions play a critical role in the plateau phase (Phase 2) of the cardiac action potential. In hypocalcemia, the reduced extracellular calcium concentration slows the influx of calcium through L-type calcium channels. This delays the completion of the plateau phase, thereby lengthening the duration of the ST segment. Since the T wave (repolarization) remains relatively unchanged, the overall effect is a **prolonged QT interval** (specifically due to the long ST segment). **2. Why the incorrect options are wrong:** * **ST segment depression:** This is typically associated with myocardial ischemia, hypokalemia, or digoxin effect, rather than calcium imbalances. * **Inversion of T wave:** This is a sign of myocardial ischemia, ventricular hypertrophy, or bundle branch blocks. In hypocalcemia, the T wave is usually upright and normal. * **Prolongation of PR segment:** This indicates a delay in AV node conduction, commonly seen in first-degree heart block or hyperkalemia, but not typically associated with hypocalcemia. **High-Yield Clinical Pearls for NEET-PG:** * **Hypocalcemia:** Prolonged ST segment $\rightarrow$ Prolonged QT interval (can predispose to Torsades de Pointes, though less common than in hypomagnesemia). * **Hypercalcemia:** Shortened ST segment $\rightarrow$ **Shortened QT interval** (the "Osborn wave" or J wave is more specific to hypothermia but can rarely be seen here). * **Mnemonic:** "Hypo-Long, Hyper-Short" (referring to the QT interval). * **Clinical Signs:** Look for Trousseau’s sign and Chvostek’s sign in the clinical stem.

Question 1

What causes the normal atrioventricular (AV) delay of 0.1 seconds?

Accepted Answer

Decrease in the number of gap junctions between cardiac cells

Answer

Decrease in the amplitude of cardiac action potential firing

Answer

Electrical resistance offered by myocytes

Answer

Lack of tight junctions between cardiac cells

Question 2

Chemoreceptors operate between which pressure range?

Accepted Answer

40-100 mm Hg

Answer

Below 90 mm Hg

Answer

70-150 mm Hg

Answer

70-220 mm Hg

Question 3

Blood flow through a vessel varies directly with which of the following?

Accepted Answer

Difference of pressure

Answer

Resistance

Answer

Viscosity

Answer

Length of the vessel

Question 4

Which of the following statements regarding fetal circulation is true?

Accepted Answer

The more oxygenated blood in the right atrium crosses the foramen ovale to the left atrium.

Answer

Fetal heart chambers work in series to effectively supply the brain and heart with higher oxygenated blood.

Answer

The ductus venosus is the main branch of the umbilical artery.

Answer

The oxygen content of blood delivered to the heart from the inferior vena cava is higher than that leaving the placenta.

Question 5

All of the following statements about the third heart sound (S3) are true, except?

Accepted Answer

Occurs due to rapid ventricular filling

Answer

May be heard in mitral regurgitation

Answer

May be heard in Atrial Septal Defect (ASD)

Answer

May be heard in Ventricular Septal Defect (VSD)

Question 6

In a patient with a cardiac output of 5 liters/min and a body surface area of 1.7 square meters, what is the cardiac index?

Accepted Answer

3 L/min/sq. m

Answer

4 L/min/sq. m

Answer

5 L/min/sq. m

Answer

2.5 L/min/sq. m

Question 7

What is the autonomic supply to the SA node?

Accepted Answer

Sympathetic, excitatory

Answer

Parasympathetic, inhibitory

Answer

Both parasympathetic and sympathetic, excitatory

Answer

Both parasympathetic and sympathetic, inhibitory

Question 8

Turbulence of blood flow increases when:

Accepted Answer

Diameter of blood vessel decreases

Answer

Viscosity decreases

Answer

Density decreases

Answer

Arteries are straight

Question 9

What are the ECG changes seen in hypocalcemia?

Accepted Answer

Prolongation of ST segment

Answer

ST segment depression

Answer

Inversion of T wave

Answer

Prolongation of PR segment

Question 10

All of the following events occur at or shortly after birth EXCEPT?

Accepted Answer

The ductus arteriosus closes, allowing blood to bypass the lungs.

Answer

The ductus arteriosus closes, ending shunting of blood from the aorta to the lungs.

Answer

The foramen ovale closes, ending the shunting of blood from the right to the left atrium.

Answer

Blood pressure in the left atrium increases.

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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