Cardiovascular System Practice Questions

Q: What is the approximate amount of blood present in the capillaries at any given time?

250 ml. **Explanation:** The total circulating blood volume in an average adult is approximately 5,000 ml. The distribution of this volume across the vascular system is uneven and is governed by the **capacitance** and **cross-sectional area** of the vessels. **Why 250 ml is correct:** Although capillaries have the largest total cross-sectional area (approx. 2500–3000 cm²), they contain only about **5% of the total blood volume**, which equates to roughly **250 ml**. This small volume is functional: it ensures that blood flow velocity is at its slowest (approx. 0.3 mm/sec), providing maximum time for the exchange of gases, nutrients, and waste products across the thin capillary walls. **Analysis of Incorrect Options:** * **B (1000 ml):** This represents roughly 20% of the blood volume, which is closer to the volume found in the systemic arteries. * **C & D (2000–2500 ml):** These values represent 40–50% of the blood volume. The **systemic veins and venules** hold the majority of the blood (approx. 60–65% or 3200 ml), acting as the "blood reservoir" or capacitance vessels. **High-Yield Facts for NEET-PG:** * **Capacitance Vessels:** Veins (hold ~64% of blood). * **Resistance Vessels:** Arterioles (site of maximum peripheral resistance). * **Exchange Vessels:** Capillaries (highest cross-sectional area, lowest velocity). * **Velocity of Flow:** Inversely proportional to the total cross-sectional area ($V = Q/A$). Therefore, velocity is highest in the aorta and lowest in the capillaries.

Q: Ejection fraction denotes the performance of which chamber?

Left ventricle. ### Explanation **1. Why Left Ventricle is Correct:** Ejection Fraction (EF) is a key physiological index used to evaluate the **systolic function** (pumping capacity) of the heart, specifically the **Left Ventricle (LV)**. It represents the percentage of blood pumped out of the LV with each contraction. * **Formula:** $EF = \frac{Stroke Volume (SV)}{End Diastolic Volume (EDV)} \times 100$ * Since the LV is responsible for systemic circulation, its performance is the primary determinant of cardiac output and clinical stability. A normal LV ejection fraction typically ranges from **55% to 70%**. **2. Why Other Options are Incorrect:** * **Left Atrium:** The atrium acts primarily as a reservoir and a conduit to the ventricle. While it has an "atrial kick," its performance is measured by volumes and strain, not ejection fraction. * **Aortic & Pulmonary Valves:** These are anatomical structures (valves) that regulate the direction of blood flow. They do not have an "ejection fraction"; their performance is measured by pressure gradients and orifice area (e.g., in stenosis or regurgitation). **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Gold Standard Measurement:** Transthoracic Echocardiography (ECHO) is the most common clinical tool, but **Cardiac MRI** is the gold standard for volume and EF assessment. * **Heart Failure Classification:** * **HFrEF** (Heart Failure with reduced EF): $\leq 40\%$ * **HFpEF** (Heart Failure with preserved EF): $\geq 50\%$ * **Right Ventricle (RV):** While the RV also has an ejection fraction (normally lower, ~45-50%), in standard clinical practice and exam questions, "Ejection Fraction" implicitly refers to the **Left Ventricle** unless specified otherwise. * **Indicator of Prognosis:** EF is the single most important predictor of survival in patients with cardiovascular disease.

Q: What is the most important factor determining the strength of a pulse?

Pulse Pressure. ### Explanation **1. Why Pulse Pressure is the Correct Answer:** The strength (or volume) of a peripheral pulse is clinically defined by the **Pulse Pressure (PP)**, which is the difference between Systolic Blood Pressure (SBP) and Diastolic Blood Pressure (DBP). * **Physiological Basis:** Pulse pressure is primarily determined by two factors: **Stroke Volume (SV)** and **Arterial Compliance**. When the heart ejects blood into the aorta, the pressure rises to its peak (systole); the magnitude of this pressure "swing" determines the tactile sensation of the pulse. A higher stroke volume or decreased arterial compliance (stiffness) leads to a wider pulse pressure and, consequently, a "bounding" or stronger pulse. **2. Why Other Options are Incorrect:** * **Mean Blood Pressure (MBP):** This represents the average pressure in the arteries throughout one cardiac cycle. While it is the critical parameter for **tissue perfusion**, it does not reflect the pulsatile nature of blood flow. A patient can have a normal MBP with a very weak pulse (e.g., in heart failure where SBP and DBP are close together). * **Total Peripheral Resistance (TPR):** TPR primarily influences **Diastolic Blood Pressure**. While high TPR can lead to hypertension, it often reduces pulse pressure by increasing the DBP, potentially making the pulse feel "thready" rather than strong. **3. High-Yield Clinical Pearls for NEET-PG:** * **Water-Hammer Pulse (Corrigan’s Pulse):** A classic example of a "strong" pulse caused by a very wide pulse pressure, typically seen in **Aortic Regurgitation**. * **Pulsus Alternans:** A sign of left ventricular failure where pulse strength alternates between strong and weak despite a regular rhythm. * **Pulsus Paradoxus:** A decrease in pulse strength (SBP drop >10 mmHg) during inspiration, classically seen in **Cardiac Tamponade**. * **Formula:** $PP = SBP - DBP$. Remember: Pulse Volume $\propto$ Stroke Volume.

Q: What is the first reactionary change to occur after vessel injury and haemorrhage?

Vasoconstriction. **Explanation:** The correct answer is **Vasoconstriction (Option A)**. When a blood vessel is injured and hemorrhage occurs, the body’s immediate priority is to minimize blood loss and maintain perfusion pressure. This is achieved through **local myogenic contraction** and **sympathetic stimulation**. 1. **Local Myogenic Spasm:** Damage to the vascular wall causes direct trauma to smooth muscle cells, leading to immediate contraction. 2. **Humoral Factors:** Platelets at the site of injury release potent vasoconstrictors like **Thromboxane A2** and **Serotonin**. 3. **Sympathetic Reflex:** The drop in blood pressure triggers the baroreceptor reflex, leading to generalized vasoconstriction to increase Total Peripheral Resistance (TPR). **Why other options are incorrect:** * **Bradycardia (Option B):** Hemorrhage typically causes **tachycardia** (increased heart rate) as a compensatory mechanism to maintain Cardiac Output ($CO = HR \times SV$). Bradycardia only occurs in terminal stages (Stage IV shock) or via the Bezold-Jarisch reflex in specific scenarios. * **Raised Cortisol (Option C):** While cortisol increases as part of the stress response, it is a hormonal change that takes minutes to hours to peak, making it much slower than the near-instantaneous vascular response. * **Raised Adrenaline (Option D):** Catecholamine release is a rapid systemic response, but the **local myogenic vasoconstriction** occurs milliseconds after the physical trauma, preceding the systemic endocrine surge. **High-Yield Clinical Pearls for NEET-PG:** * **Hemostasis Sequence:** 1. Vascular Spasm (Vasoconstriction) $\rightarrow$ 2. Platelet Plug formation $\rightarrow$ 3. Coagulation (Fibrin clot). * **Baroreceptor Reflex:** This is the most important short-term mechanism for BP regulation during hemorrhage. * **Shock Index:** Heart Rate / Systolic BP (Normal: 0.5–0.7). An increase is an early indicator of significant blood loss.

Q: Cerebral blood flow is regulated by all except?

Potassium ions. **Explanation:** Cerebral blood flow (CBF) is tightly regulated to ensure a constant supply of oxygen and glucose to the brain. The correct answer is **Potassium ions**, as they are not a primary systemic regulator of CBF, although they may play minor roles in local neurovascular coupling. **1. Why Potassium ions (Option C) is the correct answer:** While local changes in extracellular $K^+$ can cause transient vasodilation, it is not considered a primary regulatory mechanism for global cerebral blood flow. In contrast, factors like $CO_2$, $O_2$, and Mean Arterial Pressure (MAP) have profound, well-documented effects on the entire cerebral vasculature. **2. Analysis of Incorrect Options:** * **Blood Pressure (Option A):** Through **Cerebral Autoregulation**, CBF remains constant despite changes in MAP between **60 and 140 mmHg**. Outside this range, CBF becomes pressure-dependent. * **$PaCO_2$ (Option B):** This is the **most potent physiological stimulus** for CBF. Hypercapnia (high $CO_2$) causes marked vasodilation, while hypocapnia (low $CO_2$) causes vasoconstriction. * **Cerebral Metabolic Rate (Option D):** CBF is directly proportional to metabolic activity (Metabolic Autoregulation). Increased neuronal activity leads to the release of metabolites like Adenosine, $H^+$, and Nitric Oxide, which increase local blood flow. **High-Yield Facts for NEET-PG:** * **Normal CBF:** 50 ml/100g/min (approx. 750 ml/min or 15% of Cardiac Output). * **$CO_2$ Sensitivity:** A 1 mmHg rise in $PaCO_2$ increases CBF by approximately 3-4%. * **Cushing’s Reflex:** A clinical triad of hypertension, bradycardia, and irregular respiration seen in increased intracranial pressure (ICP). * **Monro-Kellie Doctrine:** The sum of volumes of brain, CSF, and intracerebral blood is constant; an increase in one must be offset by a decrease in another.

Question 1

What reflex is responsible for tachycardia during right ventricle distention?

Accepted Answer

Bainbridge reflex

Answer

Bezold-Jaisch reflex

Answer

Cushing reflex

Answer

J-reflex

Question 2

In a normal electrocardiogram (ECG or EKG), which of the following is correct?

Accepted Answer

The QRS complex results from depolarization of the ventricles.

Answer

The P wave results from repolarization of the atria.

Answer

The T wave represents repolarization of the auricles.

Answer

During the P-R interval, the ventricles contract.

Question 3

All are true regarding capillaries except?

Accepted Answer

Contain larger quantity of blood than veins

Answer

Have large total cross-sectional area

Answer

Site of gaseous exchange

Answer

Lined by endothelium

Question 4

What is the approximate amount of blood present in the capillaries at any given time?

Accepted Answer

250 ml

Answer

1000 ml

Answer

2000 ml

Answer

2500 ml

Question 5

Ejection fraction denotes the performance of which chamber?

Accepted Answer

Left ventricle

Answer

Left atrium

Answer

Aortic valve

Answer

Pulmonary valve

Question 6

What is the most important factor determining the strength of a pulse?

Accepted Answer

Pulse Pressure

Answer

Mean Blood Pressure

Answer

Total Peripheral Resistance

Answer

None of the above

Question 7

With normal cardiac function, a 10 mm Hg change in which of the following pressures would have the greatest effect on cardiac output?

Accepted Answer

Right atrial pressure

Answer

Pressure in the carotid artery

Answer

Pressure in the pulmonary artery

Answer

Aortic pressure

Question 8

Cardiac output increases by which of the following mechanisms?

Accepted Answer

Increased cardiac contractility

Answer

Standing from a lying down position

Answer

Expiration

Answer

Parasympathetic stimulation

Question 9

What is the first reactionary change to occur after vessel injury and haemorrhage?

Accepted Answer

Vasoconstriction

Answer

Bradycardia

Answer

Raised cortisol

Answer

Raised adrenaline

Question 10

Cerebral blood flow is regulated by all except?

Accepted Answer

Potassium ions

Answer

Blood pressure

Answer

PaCO2

Answer

Cerebral metabolic rate

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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