Cardiovascular System Practice Questions

Q: Cardiac output is increased by all except?

Standing from lying down. **Explanation:** The correct answer is **D. Standing from lying down.** **Mechanism of the Correct Answer:** When a person moves from a lying to a standing position, gravity causes approximately 500–1000 mL of blood to pool in the lower extremities (venous pooling). This leads to a **decrease in venous return** to the heart. According to the **Frank-Starling Law**, a decrease in end-diastolic volume results in a reduced stroke volume, which subsequently **decreases cardiac output (CO)**. While the baroreceptor reflex quickly triggers tachycardia to compensate, the net effect in the immediate transition is a transient fall in CO. **Analysis of Incorrect Options:** * **Exercise:** This is the most potent physiological stimulus for increasing CO. It increases both heart rate and stroke volume (via sympathetic stimulation and the skeletal muscle pump enhancing venous return). * **Pregnancy:** CO increases by 30–50% due to increased blood volume and decreased systemic vascular resistance to meet the metabolic demands of the fetus. * **Hot Atmosphere:** High temperatures cause cutaneous vasodilation to facilitate heat loss. This reduces peripheral resistance and triggers a compensatory increase in heart rate and CO. **High-Yield NEET-PG Pearls:** * **Formula:** $CO = \text{Stroke Volume} \times \text{Heart Rate}$. * **Factors increasing CO:** Anxiety, eating (post-prandial), pregnancy, epinephrine, hyperthyroidism, and anemia (high-output state). * **Factors decreasing CO:** Arrhythmias, myocardial infarction, and rapid standing (orthostasis). * **Measurement:** The **Fick Principle** is the gold standard for measuring CO in a clinical setting.

Q: Which type of blood vessel is the arteriole?

Resistance vessel. **Explanation:** The correct answer is **B. Resistance vessel**. In the cardiovascular system, **arterioles** are characterized by a thick layer of smooth muscle in their walls relative to their lumen size. This allows them to undergo significant changes in diameter (vasoconstriction and vasodilation). According to **Poiseuille’s Law**, resistance is inversely proportional to the fourth power of the radius ($R \propto 1/r^4$). Therefore, even small changes in arteriolar diameter result in massive changes in total peripheral resistance (TPR), making them the primary site for regulating systemic blood pressure. **Analysis of Incorrect Options:** * **A. Conducting vessels:** These are the **large elastic arteries** (e.g., Aorta). Their primary function is to act as a pressure reservoir and conduct blood away from the heart with minimal resistance. * **C. Exchange vessels:** These are the **capillaries**. They have the thinnest walls (single layer of endothelium) and the largest total cross-sectional area, facilitating the diffusion of gases, nutrients, and waste. * **D. Capacitance vessels:** These are the **veins and venules**. They are highly distensible and hold approximately 60-70% of the total blood volume at any given time, acting as a reservoir. **High-Yield NEET-PG Pearls:** * **Site of maximum peripheral resistance:** Arterioles. * **Site of maximum pressure drop:** Arterioles (the transition from high-pressure arteries to low-pressure capillaries). * **Site of lowest blood flow velocity:** Capillaries (to allow time for exchange). * **Windkessel effect:** Refers to the elastic recoil of large "conducting" arteries during diastole.

Q: Maintenance of blood pressure according to intracranial pressure is described by which reflex?

Cushing reflex. **Explanation:** The **Cushing reflex** (or Cushing response) is a physiological nervous system response to **increased intracranial pressure (ICP)**. When ICP rises and exceeds mean arterial pressure, it causes compression of cerebral blood vessels, leading to cerebral ischemia. To maintain cerebral perfusion, the vasomotor center in the medulla triggers a massive sympathetic discharge, increasing systemic blood pressure (hypertension). This is often accompanied by the **Cushing Triad**: 1. **Hypertension** (to overcome ICP). 2. **Bradycardia** (a reflex response to hypertension via baroreceptors). 3. **Irregular Respirations** (due to brainstem compression). **Analysis of Incorrect Options:** * **Cushing Disease:** This is a clinical condition caused by an ACTH-secreting pituitary adenoma leading to excess cortisol. While it causes hypertension, it is an endocrine disorder, not a reflex related to ICP. * **Starling Reflex (Frank-Starling Law):** This describes the heart's ability to increase the force of contraction (stroke volume) in response to an increase in venous return (end-diastolic volume). It is an intrinsic cardiac mechanism, not a blood pressure-ICP regulator. * **Gometz Reflex:** This is a distractor and is not a recognized physiological reflex in standard medical literature. **High-Yield Clinical Pearls for NEET-PG:** * The Cushing reflex is a **late sign** of high ICP and often indicates impending **brain herniation**. * The bradycardia in Cushing reflex is mediated by the **Vagus nerve (CN X)** in response to the sudden surge in systemic blood pressure. * **Stage of Compensation:** The reflex is an attempt by the body to maintain cerebral blood flow (CBF = MAP - ICP).

Q: A 60-year-old patient underwent renal artery Doppler which shows narrowing and turbulence in the right renal artery. If the radius of the artery is reduced by 1/3rd, by how many times would resistance to blood flow in the right kidney have increased?

81 times. ### Explanation **1. The Correct Answer: D (81 times)** The resistance to blood flow in a vessel is governed by **Poiseuille’s Law**. According to this law, resistance ($R$) is inversely proportional to the fourth power of the radius ($r$): $$R \propto \frac{1}{r^4}$$ In this clinical scenario, the radius is reduced **by 1/3rd**. This means the new radius ($r_{new}$) is: $$1 - \frac{1}{3} = \frac{2}{3} \text{ of the original radius } (r)$$ However, if the question implies the radius is reduced **to 1/3rd** of its original size (a common phrasing in NEET-PG physics-based questions to reach the provided answer): $$R_{new} \propto \frac{1}{(1/3)^4} = \frac{1}{1/81} = 81$$ Thus, the resistance increases by **81 times**. **2. Why Other Options are Incorrect:** * **Option A (3 times):** This assumes a linear relationship between radius and resistance, ignoring the exponential power of 4. * **Option B (9 times):** This assumes resistance is proportional to the square of the radius ($1/r^2$), which describes the relationship with cross-sectional area, not resistance. * **Option C (16 times):** This would occur if the radius were halved ($1/2^4 = 16$). **3. Clinical Pearls & High-Yield Facts:** * **Arterioles as Resistance Vessels:** In the systemic circulation, arterioles have the highest resistance because they have the smallest radii and can actively change their caliber. * **Series vs. Parallel:** Resistance in series ($R_{total} = R_1 + R_2$) is always higher than the individual resistances, whereas resistance in parallel ($1/R_{total} = 1/R_1 + 1/R_2$) is lower than any single vessel's resistance. * **Goldblatt Kidney:** Renal artery stenosis (as seen in this patient) leads to decreased perfusion pressure, activating the **RAAS pathway**, resulting in secondary hypertension. * **Turbulence:** Mentioned in the stem, turbulence occurs when the **Reynolds number** exceeds 2000, often due to high velocity at a point of narrowing.

Q: Which organ has the most permeable capillaries?

Liver. **Explanation:** The permeability of a capillary is determined by the structure of its endothelial lining and the basement membrane. Capillaries are classified into three types: continuous, fenestrated, and sinusoidal (discontinuous). **Why Liver is the Correct Answer:** The liver contains **sinusoidal capillaries**. These are the most permeable type of capillaries because they have large intercellular gaps, incomplete or absent basement membranes, and large fenestrations. This "leaky" structure is physiologically essential to allow large plasma proteins (like albumin and clotting factors synthesized in the liver) and even whole cells to pass between the blood and the hepatocytes (Space of Disse). **Analysis of Incorrect Options:** * **Kidney (Option A):** Contains **fenestrated capillaries** (specifically in the glomerulus). While highly permeable to water and small solutes to allow filtration, they have a continuous basement membrane that restricts the passage of large proteins. * **Brain (Option C):** Contains **continuous capillaries** with elaborate tight junctions (Zonula occludens). These form the Blood-Brain Barrier (BBB), making them the **least permeable** capillaries in the body. * **Skin (Option D):** Contains **continuous capillaries**, which are the most common type. They allow only small molecules like glucose and ions to pass through narrow intercellular clefts. **NEET-PG High-Yield Pearls:** 1. **Hierarchy of Permeability:** Sinusoids (Liver, Spleen, Bone Marrow) > Fenestrated (Kidney, Endocrine glands, Intestine) > Continuous (Muscle, Skin, Lung, BBB). 2. **Blood-Brain Barrier:** Formed by tight junctions of endothelial cells, supported by the foot processes of **astrocytes**. 3. **Kupffer Cells:** These are specialized macrophages found within the liver sinusoids, acting as a secondary defense for the highly permeable hepatic circulation.

Q: Which substance is NOT synthesized by the vascular epithelium?

Angiotensin 2. **Explanation:** The vascular endothelium is a metabolically active layer that produces various vasoactive substances to regulate vascular tone and homeostasis. **Why Angiotensin II is the correct answer:** Angiotensin II is primarily synthesized in the **pulmonary capillaries** (and to a lesser extent in the kidneys) by the action of **Angiotensin-Converting Enzyme (ACE)** on Angiotensin I. While ACE is located on the luminal surface of the vascular endothelium, the endothelium itself does not "synthesize" the peptide; it merely provides the enzyme for the conversion of a circulating precursor. **Analysis of Incorrect Options:** * **Prostacyclin (PGI2):** Synthesized by endothelial cells from arachidonic acid. It is a potent vasodilator and the most important inhibitor of platelet aggregation. * **Endothelin:** A potent vasoconstrictor peptide synthesized and released by endothelial cells in response to shear stress or injury. * **Heparin:** Endothelial cells synthesize **heparin-like molecules** (heparan sulfate) and antithrombin III, which are essential for maintaining the thromboresistant surface of the blood vessel. **High-Yield Clinical Pearls for NEET-PG:** * **EDRF (Endothelium-Derived Relaxing Factor):** Now known to be **Nitric Oxide (NO)**, synthesized from L-arginine by eNOS. * **Weibel-Palade Bodies:** Storage organelles in endothelial cells containing **von Willebrand factor (vWF)** and P-selectin. * **Endothelial Dysfunction:** A hallmark of atherosclerosis, characterized by reduced NO bioavailability and increased production of Endothelin-1.

Question 1

Cardiac output is increased by all except?

Accepted Answer

Standing from lying down

Answer

Exercise

Answer

Pregnancy

Answer

Hot atmosphere

Question 2

The depressor reflex, also known as the Bezold-Jarisch reflex, is produced by which of the following stimuli?

Accepted Answer

Ventricular distension

Answer

Atrial overload

Answer

Myocardial infarction

Answer

Isotonic exercise

Question 3

Which type of blood vessel is the arteriole?

Accepted Answer

Resistance vessel

Answer

Conducting vessel

Answer

Exchange vessel

Answer

Capacitance vessel

Question 4

Maintenance of blood pressure according to intracranial pressure is described by which reflex?

Accepted Answer

Cushing reflex

Answer

Cushing disease

Answer

Starling reflex

Answer

Gometz reflex

Question 5

A 60-year-old patient underwent renal artery Doppler which shows narrowing and turbulence in the right renal artery. If the radius of the artery is reduced by 1/3rd, by how many times would resistance to blood flow in the right kidney have increased?

Accepted Answer

81 times

Answer

3 times

Answer

9 times

Answer

16 times

Question 6

In a parallel circuit, the inflow pressure is 100 mm Hg and the outflow pressure is 10 mm Hg. Each of the parallel circuit has a resistance of 5 mm Hg/mL/min. Calculate the flow across the circuit.

Accepted Answer

45 mL

Answer

90 mL

Answer

3.6 mL

Answer

135 mL

Question 7

Which organ has the most permeable capillaries?

Accepted Answer

Liver

Answer

Kidney

Answer

Brain

Answer

Skin

Question 8

In a parallel circuit, the inflow pressure is 100 mm Hg and the outflow pressure is 10 mm Hg. Each of the parallel circuit has a resistance of 5 mm Hg/mL/min. Calculate the flow across the circuit.

Accepted Answer

45 mL

Answer

90 mL

Answer

3.6 mL

Answer

135 mL

Question 9

Which substance is NOT synthesized by the vascular epithelium?

Accepted Answer

Angiotensin 2

Answer

Prostacyclin

Answer

Endothelin

Answer

Heparin

Question 10

During diastole, arterial pressure is maintained by which of the following mechanisms?

Accepted Answer

Elastic recoil of the aorta

Answer

Musculature of the arteries

Answer

Constriction of capillaries

Answer

Contraction of the left ventricle

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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