Cardiovascular System Practice Questions

Q: What is the largest compliance in the circulatory system?

Veins. **Explanation:** **1. Why Veins are the Correct Answer:** Compliance (or capacitance) is defined as the change in volume per unit change in pressure ($C = \Delta V / \Delta P$). In the circulatory system, **veins** have the highest compliance—approximately **24 times** that of arteries. This is due to their thin, distensible walls and larger luminal diameters. Because of this high compliance, veins can accommodate large volumes of blood (about 60-70% of total blood volume) with minimal increases in pressure, acting as the body’s primary **blood reservoir**. **2. Why Other Options are Incorrect:** * **Arteries & Aorta:** These are "resistance" and "conduit" vessels, respectively. They have thick, muscular, and elastic walls designed to withstand high pressures. Consequently, they are much stiffer (less compliant) than veins. A small increase in arterial volume leads to a significant rise in pressure. * **Capillaries:** While numerous, individual capillaries have very small diameters and lack the distensible wall structure required for high compliance. Their primary function is exchange, not storage. **3. NEET-PG High-Yield Pearls:** * **Capacitance Vessels:** Veins are known as capacitance vessels, while arterioles are known as resistance vessels. * **Formula:** Compliance is the inverse of **Elastance** ($E = 1/C$). As age increases or in conditions like atherosclerosis, arterial compliance decreases (vessels become stiffer). * **Sympathetic Effect:** Sympathetic stimulation decreases venous compliance (venoconstriction), shifting blood from the peripheral veins into the heart to increase stroke volume (Frank-Starling mechanism). * **Specific Ratio:** Systemic veins are about 8 times more distensible than systemic arteries, and their volume is 3 times larger, leading to the 24x total compliance figure.

Q: The fourth heart sound is caused by:

Ventricular filling. ### Explanation **Correct Answer: C. Ventricular filling** The **fourth heart sound (S4)**, also known as the "atrial gallop," occurs during the late phase of ventricular diastole. It is caused by the **atrial kick**, where the atria contract to force the final 20–30% of blood into a stiff or non-compliant ventricle. This sudden surge of blood causes vibrations in the ventricular walls, papillary muscles, and chordae tendineae. Because it occurs just before the first heart sound (S1), it is described as having a "presystolic" rhythm. **Analysis of Incorrect Options:** * **Option A (Closure of semilunar valves):** This produces the **second heart sound (S2)**, marking the beginning of diastole. * **Option B (Vibrations during systole):** Heart sounds are primarily associated with valve closures or filling phases. While S1 occurs at the start of systole, S4 is strictly a diastolic event. * **Option D (Closure of AV valves):** This produces the **first heart sound (S1)**, marking the beginning of ventricular systole. **High-Yield Clinical Pearls for NEET-PG:** * **Pathological Significance:** S4 is almost always pathological (unlike S3, which can be physiological in young adults/athletes). It indicates **decreased ventricular compliance** (stiffness). * **Common Causes:** Left ventricular hypertrophy (due to systemic hypertension or aortic stenosis), ischemic heart disease, and hypertrophic cardiomyopathy (HCM). * **Auscultation:** Best heard with the **bell** of the stethoscope at the apex in the left lateral decubitus position. * **The "Tennessee" Rhythm:** S4-S1-S2 creates a cadence similar to the word "Ten-nes-see." * **Absent in Atrial Fibrillation:** Since S4 requires active atrial contraction, it **cannot** occur in patients with atrial fibrillation.

Q: What is the basal cardiac output in an adult?

5 litres. **Explanation:** **Cardiac Output (CO)** is defined as the volume of blood pumped by each ventricle per minute. It is the product of **Stroke Volume (SV)** and **Heart Rate (HR)** ($CO = SV \times HR$). 1. **Why 5 Litres is Correct:** In a healthy adult at rest (basal state), the average stroke volume is approximately **70 mL** and the average heart rate is **72 beats per minute**. Calculation: $70\text{ mL} \times 72\text{ bpm} \approx 5,040\text{ mL/min}$ or roughly **5 L/min**. This value represents the standard physiological baseline required to meet the metabolic demands of the body's tissues at rest. 2. **Why Other Options are Incorrect:** * **A (7.5 L):** This is higher than the basal rate and may be seen during mild exertion or in hyperdynamic states (e.g., pregnancy or hyperthyroidism). * **C & D (12 L and 10 L):** These values are significantly higher than resting levels. While the heart can reach these outputs during moderate to heavy exercise (the maximum CO can reach 20–25 L/min in athletes), they do not represent the "basal" state. **High-Yield Clinical Pearls for NEET-PG:** * **Cardiac Index (CI):** Since CO varies with body size, the Cardiac Index is a more accurate clinical parameter. It is $CO \div \text{Body Surface Area}$. Normal range: **2.5 to 4.2 L/min/m²**. * **Distribution:** At rest, the **Liver (27%)** and **Kidneys (22%)** receive the highest percentage of cardiac output, while the heart itself (coronary circulation) receives about 5%. * **Fick’s Principle:** The gold standard for measuring CO. $CO = \text{Oxygen consumption} \div (\text{Arterial } O_2 \text{ content} - \text{Venous } O_2 \text{ content})$.

Q: Cushing's reflex is characterized by all of the following EXCEPT:

Increased heart rate. **Explanation:** Cushing’s reflex (or the Cushing triad) is a physiological nervous system response to **increased intracranial pressure (ICP)**. It is a compensatory mechanism aimed at maintaining cerebral perfusion pressure (CPP). **1. Why "Increased heart rate" is the correct answer (The Exception):** In Cushing’s reflex, the heart rate **decreases (Bradycardia)**, it does not increase. When ICP rises, the brainstem experiences ischemia. The sympathetic nervous system initially triggers a massive pressor response to increase systemic blood pressure. This high blood pressure is sensed by baroreceptors in the carotid sinus and aortic arch, which then trigger a compensatory **parasympathetic (vagal) response**, leading to reflex bradycardia. **2. Analysis of Incorrect Options:** * **Increased systolic blood pressure:** This is a hallmark of the reflex. The body raises the Mean Arterial Pressure (MAP) to overcome the high ICP and force blood into the brain (CPP = MAP - ICP). This often results in a **widened pulse pressure**. * **Irregular respiration:** As the brainstem (specifically the medulla) becomes compressed or ischemic due to high ICP, the normal respiratory rhythm is disrupted, often leading to Cheyne-Stokes breathing or ataxic respirations. **Clinical Pearls for NEET-PG:** * **The Cushing Triad:** 1. Hypertension (with widened pulse pressure), 2. Bradycardia, 3. Irregular respirations. * **Significance:** It is a late sign of high ICP and suggests imminent **brain herniation**. * **Mechanism:** Ischemia of the vasomotor center in the medulla → Sympathetic surge (Hypertension) → Baroreceptor activation → Vagal stimulation (Bradycardia).

Q: Which ion is primarily responsible for the depolarization phase of the cardiac action potential?

Sodium (Na+). **Explanation:** The cardiac action potential varies between non-pacemaker (ventricular/atrial) and pacemaker cells. In **non-pacemaker (fast-response) cells**, which represent the bulk of the myocardium, the **depolarization phase (Phase 0)** is primarily caused by the rapid influx of **Sodium (Na+)** ions through voltage-gated "fast" sodium channels. This rapid influx causes the membrane potential to shift from approximately -90mV to +20mV. **Analysis of Options:** * **B. Sodium (Na+) [Correct]:** Responsible for Phase 0 depolarization in ventricular, atrial, and Purkinje fibers. * **A. Potassium (K+):** Primarily responsible for **repolarization** (Phases 1, 2, and 3). Efflux of K+ restores the negative resting membrane potential. * **C. Calcium (Ca+2):** Responsible for the **plateau phase (Phase 2)** in ventricular cells and, importantly, for the **depolarization (Phase 0)** in **pacemaker cells** (SA/AV nodes). However, in the context of a general "cardiac action potential" question, Na+ is the standard answer for the rapid upstroke. * **D. Chloride (Cl-):** Plays a minor role in early transient repolarization (Phase 1) but does not contribute to depolarization. **High-Yield Clinical Pearls for NEET-PG:** * **Phase 0 (Depolarization):** Target of **Class I Antiarrhythmics** (e.g., Lidocaine, Flecainide), which block fast Na+ channels. * **Pacemaker Potential:** Unlike ventricular cells, the SA node depolarization is mediated by **L-type Calcium channels**, not sodium channels. * **Tetrodotoxin (TTX):** A potent toxin that specifically inhibits these fast voltage-gated Na+ channels, preventing depolarization. * **Phase 2 (Plateau):** Unique to cardiac muscle; caused by a balance between Ca+2 influx and K+ efflux, ensuring a long refractory period to prevent tetany.

Q: A healthy 28-year-old woman stands up from a supine position. Which of the following cardiovascular changes is MOST likely to occur?

Increased heart rate. **Explanation:** When a person moves from a supine to a standing position, gravity causes approximately 500–1000 mL of blood to pool in the lower extremities. This leads to a **decrease in venous return**, which reduces stroke volume and cardiac output, causing a transient drop in arterial blood pressure. **Why the correct answer is right:** The drop in blood pressure is sensed by **high-pressure baroreceptors** (located in the carotid sinus and aortic arch). This triggers the **Baroreceptor Reflex**, which leads to: 1. **Decreased parasympathetic (vagal) activity** to the SA node. 2. **Increased sympathetic activity** to the heart and peripheral vasculature. The immediate compensatory response to maintain cardiac output is an **increase in heart rate (tachycardia)**. **Why the incorrect options are wrong:** * **A. Decreased myocardial contractility:** Sympathetic stimulation actually *increases* contractility (positive inotropy) to help maintain stroke volume. * **B. Decreased total peripheral resistance (TPR):** Sympathetic outflow causes alpha-1 mediated vasoconstriction of arterioles, which *increases* TPR to support blood pressure. * **C. Dilation of large veins:** To counteract venous pooling, the sympathetic system causes **venoconstriction** (not dilation) to shift blood toward the heart and increase preload. **High-Yield NEET-PG Pearls:** * **Orthostatic Hypotension:** Defined as a drop in systolic BP >20 mmHg or diastolic BP >10 mmHg within 3 minutes of standing. * **Afferent Pathway:** Carotid sinus (CN IX - Glossopharyngeal) and Aortic arch (CN X - Vagus). * **Integration Center:** Nucleus Tractus Solitarius (NTS) in the medulla. * **The "Initial" response** to standing is always a compensatory increase in sympathetic tone.

Question 1

What is the largest compliance in the circulatory system?

Accepted Answer

Veins

Answer

Arteries

Answer

Capillaries

Answer

Aorta

Question 2

All of the following statements about myocardial oxygen demand is true, except?

Accepted Answer

Is negligible when heart is at rest

Answer

Correlates with heart rate

Answer

Is proportional to external cardiac work

Answer

Depends upon duration of systole

Question 3

Which of the following statements regarding blood pressure measurement is incorrect?

Accepted Answer

The blood pressure cuff should be placed at a higher level than the heart.

Answer

The bladder of the blood pressure cuff should cover more than 80% of the arm circumference.

Answer

The patient should be in a resting position.

Answer

The cuff should be tied over the upper arm.

Question 4

The fourth heart sound is caused by:

Accepted Answer

Ventricular filling

Answer

Closure of the aortic and pulmonary valves

Answer

Vibrations in the ventricular wall during systole

Answer

Closure of the mitral and tricuspid valves

Question 5

What is the basal cardiac output in an adult?

Accepted Answer

5 litres

Answer

7.5 litres

Answer

12 litres

Answer

10 litres

Question 6

Cushing's reflex is characterized by all of the following EXCEPT:

Accepted Answer

Increased heart rate

Answer

Increased systolic blood pressure

Answer

Irregular respiration

Answer

None of the above

Question 7

If both carotids are occluded proximal to the carotid bifurcation, what physiological changes would occur?

Accepted Answer

Decreased blood pressure and increased heart rate

Answer

Increased blood pressure and decreased heart rate

Answer

Decreased blood pressure and decreased heart rate

Answer

Increased blood pressure and increased heart rate

Question 8

In a measurement of cardiac output using the Fick principle, the O2 concentrations of mixed venous and arterial blood are 16 and 20 ml/100 ml, respectively, and the O2 consumption is 300 ml/min. The cardiac output in liters/min is?

Accepted Answer

7.5

Answer

5

Answer

8

Answer

9

Question 9

Which ion is primarily responsible for the depolarization phase of the cardiac action potential?

Accepted Answer

Sodium (Na+)

Answer

Potassium (K+)

Answer

Calcium (Ca+2)

Answer

Chloride (Cl-)

Question 10

A healthy 28-year-old woman stands up from a supine position. Which of the following cardiovascular changes is MOST likely to occur?

Accepted Answer

Increased heart rate

Answer

Decreased myocardial contractility

Answer

Decreased total peripheral resistance

Answer

Dilation of large veins

Cardiovascular System — MCQs

Cardiovascular System — MCQs

On this page

Practice by Chapter

Want unlimited practice?