Cardiovascular System Practice Questions

Q: The 'red reaction' in the triple response is due to which of the following mechanisms?

Capillary dilation. The **Triple Response of Lewis** is a physiological reaction of the skin to mechanical injury (like firm stroking). It consists of three distinct stages: the Red Reaction, the Flare, and the Wheal. ### 1. Why "Capillary Dilation" is Correct The **Red Reaction** is the first component of the triple response, appearing within 10 seconds. It is caused by the **dilation of precapillary sphincters and capillaries** in the immediate area of the stimulus. This localized vasodilation is mediated by the release of histamine and other autacoids from mast cells due to direct mechanical trauma. ### 2. Analysis of Incorrect Options * **A. Local Edema:** This describes the **Wheal**, the third stage of the response. It occurs due to increased capillary permeability leading to fluid exudation into the interstitial space. * **C. Axon Reflex:** This is the mechanism behind the **Flare** (the second stage). It involves an antidromic impulse traveling through sensory nerve fibers, causing widespread arteriolar dilation beyond the site of injury. * **D. Decreased permeability:** This is incorrect because the triple response involves an *increase* in permeability (leading to the wheal), not a decrease. ### 3. High-Yield Facts for NEET-PG * **Sequence:** Red Reaction (Capillary dilation) → Flare (Arteriolar dilation via Axon reflex) → Wheal (Increased permeability/Exudation). * **Mediator:** **Histamine** is the primary chemical mediator involved in all three stages. * **The Axon Reflex** is unique because it does not involve the CNS; it is a local peripheral nerve reflex. * **Clinical Correlation:** The triple response is exaggerated in **Dermatographism**, a form of physical urticaria.

Q: Baroreceptor stimulation would result in what change?

Decreased sympathetic discharge to heart. ### Explanation **Concept:** The baroreceptor reflex is the body's primary mechanism for short-term blood pressure (BP) regulation. Baroreceptors are stretch receptors located in the **carotid sinus** (via Glossopharyngeal nerve) and **aortic arch** (via Vagus nerve). When BP rises, these receptors are stretched, increasing their firing rate to the **Nucleus Tractus Solitarius (NTS)** in the medulla. **Why Option C is Correct:** Stimulation of the NTS leads to two simultaneous responses: 1. **Inhibition of the Vasomotor Center:** This reduces sympathetic outflow to the heart and peripheral blood vessels. 2. **Stimulation of the Cardioinhibitory Center (Nucleus Ambiguus):** This increases parasympathetic (vagal) outflow. Therefore, **decreased sympathetic discharge** to the heart reduces heart rate and contractility, helping to lower BP back to normal. **Why Other Options are Incorrect:** * **A & B:** Baroreceptor stimulation *increases* vagal activity and *decreases* heart rate (bradycardia) to compensate for high BP. * **D:** It leads to a *decrease* in vasomotor tone (vasodilation) by inhibiting sympathetic vasoconstrictor nerves, thereby reducing peripheral resistance. --- ### High-Yield NEET-PG Pearls * **Location:** Carotid sinus baroreceptors are more sensitive than aortic arch receptors; they respond to both increases and decreases in BP, whereas aortic receptors primarily respond to increases. * **Carotid Sinus Massage:** Clinically used to terminate Paroxysmal Supraventricular Tachycardia (PSVT) because it mimics high BP, triggering the reflex to increase vagal tone and slow the heart rate. * **Denervation:** If baroreceptor nerves are cut, the brain perceives "low BP," leading to persistent sympathetic overactivity and hypertension.

Q: Which of the following is not a measure of stroke volume?

Ejection fraction times cardiac output. **Explanation:** **Stroke Volume (SV)** is the volume of blood pumped by the left ventricle per heartbeat. To identify the incorrect measure, we must evaluate the mathematical relationships between cardiac parameters. **1. Why Option C is the Correct Answer (The Incorrect Measure):** Stroke volume is a component of Cardiac Output (CO), not a product of it. The formula for Cardiac Output is $CO = SV \times HR$. Therefore, multiplying Ejection Fraction (EF) by Cardiac Output does not yield a physiologically recognized volume. This option is mathematically and conceptually incorrect. **2. Analysis of Incorrect Options (Correct Measures of SV):** * **Option A (LVEDV – LVESV):** This is the standard definition of SV. It represents the difference between the volume of blood in the ventricle at the end of filling (diastole) and the volume remaining after contraction (systole). * **Option B (EF × LVEDV):** Ejection Fraction is defined as the fraction of blood ejected from the LVEDV ($EF = SV / LVEDV$). Rearranging this formula gives $SV = EF \times LVEDV$. * **Option D (CO / HR):** Since $Cardiac\ Output = Stroke\ Volume \times Heart\ Rate$, dividing CO by HR mathematically isolates the Stroke Volume. **Clinical Pearls for NEET-PG:** * **Normal Values:** Average SV is **70 mL**; average LVEDV is **120 mL**; average LVESV is **50 mL**. * **Ejection Fraction:** Normal range is **55–65%**. It is the most common clinical index of left ventricular systolic function. * **Determinants of SV:** SV is regulated by **Preload** (proportional via Frank-Starling Law), **Afterload** (inversely proportional), and **Inotropy** (contractility). * **Pulse Pressure:** In clinical practice, pulse pressure (Systolic BP - Diastolic BP) is often used as a surrogate indicator of stroke volume.

Q: The wave shown in the provided photograph is due to which of the following?

Atrial depolarization. ***Atrial depolarization*** - The **P wave** on ECG represents **atrial depolarization**, which is the electrical activation of the atria causing them to contract. - This wave occurs first in the cardiac cycle, initiating the coordinated sequence of heart contraction. *Atrial repolarization* - Atrial repolarization produces the **Ta wave**, which is typically **obscured by the QRS complex** and not visible on standard ECG. - This electrical recovery of the atria occurs simultaneously with ventricular depolarization, making it undetectable. *Ventricular depolarization* - Ventricular depolarization is represented by the **QRS complex**, which is much larger and more prominent than the P wave. - This represents the electrical activation of the **ventricles**, causing the main pumping action of the heart. *Ventricular repolarization* - Ventricular repolarization corresponds to the **T wave** on ECG, representing electrical recovery of the ventricles. - This wave follows the QRS complex and is typically **upright** in most leads, indicating ventricular relaxation.

Q: Isovolumetric relaxation proceeds during which phase of the cardiac cycle?

Ventricular relaxation. **Explanation:** **Isovolumetric relaxation (IVR)** is a crucial phase of the cardiac cycle that occurs during **early ventricular diastole (ventricular relaxation)**. It begins immediately after the closure of the semilunar valves (Aortic and Pulmonary) and ends when the Atrioventricular (AV) valves open. 1. **Why Option B is correct:** During this phase, the ventricles begin to relax, causing intraventricular pressure to drop rapidly. However, because the ventricular pressure is still higher than atrial pressure but lower than arterial pressure, **all four valves are closed**. Since no blood enters or leaves the ventricles, the volume remains constant (isovolumetric) while the pressure falls. 2. **Why other options are incorrect:** * **Ventricular ejection:** This is a phase of ventricular *systole* where the semilunar valves are open and blood is pumped out. * **Atrial contraction:** This occurs at the end of ventricular diastole (the "atrial kick") to complete ventricular filling. * **Atrial relaxation:** This occurs simultaneously with ventricular contraction (systole) and is not the primary driver of IVR. **High-Yield NEET-PG Pearls:** * **Duration:** IVR is the second shortest phase of the cardiac cycle (~0.06 - 0.08s). * **Heart Sounds:** The **Second Heart Sound (S2)** marks the *beginning* of this phase (closure of semilunar valves). * **Pressure Dynamics:** This phase shows the steepest decline in ventricular pressure on a Wiggers diagram. * **Volume:** The volume of blood remaining in the ventricle during this phase is the **End-Systolic Volume (ESV)**, typically ~50-60 mL.

Q: From the left ventricular pressure-volume loop, calculate the ejection fraction.

54%. ***54%*** - **Ejection fraction (EF)** is calculated using the formula: EF = (SV/EDV) × 100, where **stroke volume (SV) = EDV - ESV**. - From the pressure-volume loop, with **EDV = 120 mL** and **ESV = 55 mL**, the calculation yields: EF = (65/120) × 100 = 54%. *58%* - This value would require a **stroke volume of approximately 70 mL** with the same EDV of 120 mL. - The **ESV would need to be 50 mL**, which doesn't match the pressure-volume loop measurements. *60%* - This percentage corresponds to a **stroke volume of 72 mL** and an **ESV of 48 mL** with EDV = 120 mL. - The loop demonstrates a higher **end-systolic volume** than what would produce this ejection fraction. *65%* - This value represents a **stroke volume of 78 mL**, indicating an **ESV of only 42 mL**. - Such a low end-systolic volume would indicate **superior cardiac function** beyond what the pressure-volume loop displays.

Q: What does the inward flow of Na+ in the heart lead to?

Action potential. **Explanation:** The correct answer is **Action Potential** (specifically the rapid depolarization phase). In cardiac physiology, the initiation of an action potential in both ventricular myocytes and the conduction system (Purkinje fibers) is driven by the rapid influx of sodium ions ($Na^+$). When the cell membrane reaches a threshold potential, **voltage-gated fast $Na^+$ channels** open, leading to a massive inward current ($I_{Na}$). This rapid influx causes the membrane potential to shift from a negative resting state (approx. -90mV) to a positive value (approx. +20mV), characterizing **Phase 0** of the cardiac action potential. **Analysis of Incorrect Options:** * **A. Plateau phase:** This is **Phase 2** of the action potential. It is primarily maintained by the inward flow of **Calcium ($Ca^{2+}$)** through L-type channels, balanced by an outward flow of Potassium ($K^+$). * **C. Repolarization:** This occurs during **Phases 1, 2, and 3**. It is primarily driven by the **outward flow of Potassium ($K^+$)** ions, which restores the negative resting membrane potential. * **D. No change:** Inward $Na^+$ flow causes a significant electrical shift (depolarization), which is the fundamental basis of cardiac excitability. **High-Yield Clinical Pearls for NEET-PG:** * **Phase 0 (Depolarization):** Driven by $Na^+$ influx in myocytes, but by **$Ca^{2+}$ influx** in the SA/AV nodes (slow response tissues). * **Class I Antiarrhythmics:** These drugs (e.g., Lidocaine, Flecainide) work specifically by blocking these fast $Na^+$ channels, thereby slowing the rate of Phase 0 depolarization. * **Tetrodotoxin:** A potent toxin that inhibits these voltage-gated $Na^+$ channels, preventing action potential generation.

Question 1

A patient has an oxygen consumption of 240 ml/min, a pulmonary vein oxygen concentration of 180 ml/L of blood, and a pulmonary artery oxygen concentration of 160 ml/L of blood. What is the cardiac output in L/min?

Accepted Answer

12

Answer

8

Answer

10

Answer

14

Question 2

The 'red reaction' in the triple response is due to which of the following mechanisms?

Accepted Answer

Capillary dilation

Answer

Local edema

Answer

Axon reflex

Answer

Decreased permeability of capillaries

Question 3

Baroreceptor stimulation would result in what change?

Accepted Answer

Decreased sympathetic discharge to heart

Answer

Decreased vagal activity

Answer

Increased heart rate

Answer

Increased vasomotor tone

Question 4

What is the function of the Wenckebach bundle?

Accepted Answer

A bundle that relays impulses from the SA node to the AV node

Answer

Involved in the heart block

Answer

The fastest conducting pathway in the heart

Answer

An abnormal connection between the right atrium and ventricles

Question 5

Which of the following is not a measure of stroke volume?

Accepted Answer

Ejection fraction times cardiac output

Answer

Left ventricular end-diastolic volume minus left ventricular end-systolic volume

Answer

Ejection fraction times left ventricular end-diastolic volume

Answer

Cardiac output divided by heart rate

Question 6

The wave shown in the provided photograph is due to which of the following?

Accepted Answer

Atrial depolarization

Answer

Atrial repolarization

Answer

Ventricular depolarization

Answer

Ventricular repolarization

Question 7

Isovolumetric relaxation proceeds during which phase of the cardiac cycle?

Accepted Answer

Ventricular relaxation

Answer

Ventricular ejection

Answer

Atrial contraction

Answer

Atrial relaxation

Question 8

From the left ventricular pressure-volume loop, calculate the ejection fraction.

Accepted Answer

54%

Answer

58%

Answer

60%

Answer

65%

Question 9

What does the inward flow of Na+ in the heart lead to?

Accepted Answer

Action potential

Answer

Plateau phase

Answer

Repolarization

Answer

No change

Question 10

Which of the following causes maximal cerebral vasodilation?

Accepted Answer

Hypercarbia

Answer

Hypoxia

Answer

Lactic Acidosis

Answer

Exercise

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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