Cardiovascular System Practice Questions

Q: Which of the following is an endothelial smooth muscle relaxing factor?

Nitric oxide. **Explanation:** The vascular endothelium plays a critical role in regulating vascular tone by secreting paracrine substances. **Nitric Oxide (NO)**, formerly known as **Endothelium-Derived Relaxing Factor (EDRF)**, is the primary mediator of vasodilation produced by endothelial cells. 1. **Why Nitric Oxide is Correct:** NO is synthesized from **L-arginine** by the enzyme endothelial Nitric Oxide Synthase (eNOS). Once released, it diffuses into the adjacent vascular smooth muscle cells and activates **soluble Guanylyl Cyclase (sGC)**. This increases intracellular **cGMP** levels, which leads to protein kinase G activation, sequestration of calcium, and subsequent smooth muscle relaxation (vasodilation). 2. **Why the Other Options are Incorrect:** * **Angiotensin (specifically Angiotensin II):** A potent **vasoconstrictor** produced via the Renin-Angiotensin-Aldosterone System (RAAS). It acts on $AT_1$ receptors to increase blood pressure. * **Dopamine:** While it has complex effects, at high doses it acts on $\alpha_1$ receptors causing **vasoconstriction**. At low doses, it causes vasodilation in renal/mesenteric beds, but it is a catecholamine/neurotransmitter, not a primary "endothelial relaxing factor." * **Vasopressin (ADH):** As the name suggests, it is a powerful **vasoconstrictor** (acting on $V_1$ receptors) released from the posterior pituitary to increase peripheral resistance. **High-Yield Clinical Pearls for NEET-PG:** * **Other Endothelial Vasodilators:** Prostacyclin ($PGI_2$) and Endothelium-derived hyperpolarizing factor (EDHF). * **Endothelial Vasoconstrictors:** **Endothelin-1** (the most potent endogenous vasoconstrictor), Thromboxane $A_2$. * **Pharmacology Link:** Nitroglycerin and Nitroprusside work by releasing NO, mimicking the endogenous EDRF mechanism to treat angina and hypertensive emergencies.

Q: Afterload is best determined by?

Peripheral resistance. **Explanation:** **Afterload** is defined as the "load" or resistance against which the heart must pump to eject blood during systole. In the left ventricle, the primary determinant of afterload is the **Total Peripheral Resistance (TPR)** or Systemic Vascular Resistance. 1. **Why Peripheral Resistance is Correct:** According to Laplace’s Law and basic hemodynamics, the ventricle must generate enough pressure to overcome the resistance offered by the systemic arterioles. When peripheral resistance increases (e.g., via vasoconstriction), the afterload increases, requiring the heart to work harder to open the aortic valve and eject blood. 2. **Why Other Options are Incorrect:** * **End-Diastolic Volume (EDV):** This represents **Preload**, which is the degree of stretch on the ventricular myocardium at the end of diastole (Frank-Starling Law). * **End-Systolic Volume (ESV):** This is the volume of blood remaining in the ventricle after contraction. While afterload affects ESV (high afterload increases ESV), it does not *determine* it. * **Compliance:** This refers to the distensibility of the vessels or heart chambers. While aortic compliance affects systolic blood pressure, it is not the primary clinical determinant of afterload compared to resistance. **High-Yield Clinical Pearls for NEET-PG:** * **Preload** is clinically measured by Pulmonary Capillary Wedge Pressure (PCWP) for the left heart and Central Venous Pressure (CVP) for the right heart. * **Afterload** is clinically represented by Mean Arterial Pressure (MAP) or Systemic Vascular Resistance (SVR). * **Conditions increasing Afterload:** Hypertension, Aortic Stenosis (where the valve itself provides resistance), and Polycythemia (increased viscosity). * **Effect of Afterload:** An acute increase in afterload leads to a **decrease in Stroke Volume** and an increase in myocardial oxygen demand.

Q: Cardiac contractility is inhibited by which of the following factors?

Decreased phosphate (↓PO4). **Explanation:** **Correct Option: D. Decreased phosphate (↓PO4)** Cardiac contractility (inotropy) is heavily dependent on the availability of **Adenosine Triphosphate (ATP)**. Phosphorus is a critical structural component of ATP and Creatine Phosphate. In states of severe hypophosphatemia, there is a depletion of intracellular ATP stores, which impairs the cross-bridge cycling between actin and myosin filaments. This leads to myocardial depression and decreased contractility, which can clinically manifest as heart failure or difficulty weaning from a ventilator. **Analysis of Incorrect Options:** * **A. Digitalis use:** Digitalis (Digoxin) **increases** contractility. It inhibits the Na+/K+ ATPase pump, leading to an increase in intracellular Na+, which subsequently slows the Na+/Ca2+ exchanger. This results in higher intracellular Ca2+ levels, enhancing inotropy. * **B. Respiratory acidosis:** While acute acidosis (low pH) generally depresses the myocardium by competing with Ca2+ for binding sites on Troponin C, **Respiratory Acidosis** specifically (increased CO2) often triggers a compensatory **sympathetic surge**. This catecholamine release typically maintains or increases contractility in vivo, making it a less definitive inhibitor than electrolyte depletion. * **C. Metabolic alkalosis:** Alkalosis generally does not inhibit contractility; in fact, an increase in pH can slightly increase the calcium sensitivity of myofilaments. **High-Yield NEET-PG Pearls:** * **Positive Inotropes:** Catecholamines (via β1 receptors), Digoxin, Hypercalcemia, and Caffeine. * **Negative Inotropes:** Hypocalcemia, Hyperkalemia, β-blockers, Calcium channel blockers, and severe Hypophosphatemia. * **Bowditch Effect:** An increase in heart rate increases the force of contraction (Treppe phenomenon) due to the accumulation of intracellular calcium.

Q: All of the following statements are false about stroke volume EXCEPT:

Decreases with an increase in heart rate. **Explanation:** Stroke Volume (SV) is the volume of blood pumped by the left ventricle per beat. It is determined by three primary factors: **Preload** (End-Diastolic Volume), **Afterload** (Systemic Vascular Resistance), and **Contractility**. **Why Option C is Correct:** The relationship between heart rate (HR) and SV is inverse at high physiological ranges. As heart rate increases significantly, the duration of **diastole** (specifically the rapid filling phase) decreases. Since the heart has less time to fill with blood, the End-Diastolic Volume (EDV) drops. According to the Frank-Starling Law, a lower EDV leads to a lower Stroke Volume. Therefore, a marked increase in heart rate leads to a decrease in SV. **Analysis of Incorrect Options:** * **Option A & B:** These statements are technically incomplete or incorrectly phrased in the context of "All are false EXCEPT." While SV is *influenced* by afterload and preload, Option B uses the incorrect term "pre-diastolic volume" (the correct term is **End-Diastolic Volume**). * **Option D:** This is the opposite of the physiological reality. While Cardiac Output (CO = SV × HR) may initially increase with HR, the SV itself does not increase; it eventually plateaus and then declines due to shortened filling time. **High-Yield Clinical Pearls for NEET-PG:** * **Frank-Starling Law:** Stroke volume increases in response to an increase in the volume of blood filling the heart (EDV), stretching the myocardial fibers to an optimal length. * **Cardiac Output:** In a healthy individual, CO is maintained during moderate exercise because the increase in HR compensates for the slight fall in SV. * **Afterload:** An increase in afterload (e.g., hypertension) *decreases* stroke volume. * **Contractility:** Positive inotropes (like Digoxin or Adrenaline) increase SV without changing the EDV.

Q: Pressure on the carotid sinus causes which of the following?

Reflex bradycardia. **Explanation:** The **carotid sinus** is a dilated area at the base of the internal carotid artery that functions as a high-pressure **baroreceptor**. When pressure is applied to the carotid sinus (either via increased arterial blood pressure or external massage), the stretch-sensitive receptors are activated. 1. **Mechanism:** Afferent impulses are carried via the **Hering’s nerve** (a branch of the Glossopharyngeal nerve, CN IX) to the Nucleus Tractus Solitarius (NTS) in the medulla. 2. **Response:** The medulla responds by increasing parasympathetic (vagal) outflow and inhibiting sympathetic activity. The increased vagal tone acts on the SA node to decrease the heart rate, resulting in **reflex bradycardia**, and on the peripheral vasculature to cause vasodilation (hypotension). **Analysis of Incorrect Options:** * **Tachycardia (C):** This is the opposite of the baroreceptor reflex. Tachycardia occurs when baroreceptor firing *decreases* (e.g., during hemorrhage or standing up). * **Hyperapnea (A) and Dyspnea (D):** These relate to the **carotid body**, not the carotid sinus. The carotid body contains *chemoreceptors* that respond to hypoxia (low $PaO_2$), hypercapnia, and acidosis to increase the rate and depth of respiration. **Clinical Pearls for NEET-PG:** * **Carotid Sinus Hypersensitivity:** In some elderly individuals, even minor pressure (like a tight collar) can trigger an exaggerated reflex, leading to syncope. * **Carotid Sinus Massage:** A clinical maneuver used to terminate **Paroxysmal Supraventricular Tachycardia (PSVT)** by increasing vagal tone. * **Mnemonic for Innervation:** **S**inus is **N**ine (CN IX), **A**ortic arch is **T**en (CN X). Both carry afferents to the medulla.

Q: What is the approximate rate of lymph flow in the human body?

120 ml/hr. **Explanation:** The correct answer is **120 ml/hr**. **1. Understanding the Concept:** Lymph is formed from interstitial fluid that enters the lymphatic capillaries. In a resting human, the total thoracic duct lymph flow is approximately **100 ml per hour**, and an additional **20 ml per hour** flows into the circulation through other channels (like the right lymphatic duct). This brings the total estimated lymph flow to approximately **120 ml/hr**, which equates to roughly **2 to 3 liters per day**. This mechanism is crucial for returning filtered plasma proteins and excess fluid back to the venous circulation to maintain fluid homeostasis. **2. Analysis of Incorrect Options:** * **A (10 ml/hr) & B (20 ml/hr):** These values are far too low. At this rate, the body would fail to return the 2-3 liters of fluid filtered out of the capillaries daily, leading to massive systemic edema. * **C (50 ml/hr):** While higher, this still only accounts for about 1.2 liters per day, which is significantly less than the physiological average required to maintain oncotic and hydrostatic balance. **3. NEET-PG High-Yield Pearls:** * **Factors increasing lymph flow:** Increased capillary hydrostatic pressure, decreased plasma colloid osmotic pressure, increased interstitial fluid protein concentration, and increased capillary permeability. * **The "Lymphatic Pump":** Lymph flow is facilitated by the intrinsic contraction of smooth muscle in the lymphatic vessel walls (distension triggers contraction) and extrinsic compression (skeletal muscle pump). * **Protein Transport:** The lymphatic system is the **only** route by which high-molecular-weight proteins can be returned to the blood from interstitial spaces. * **Fat Absorption:** Remember that long-chain fatty acids are absorbed via lacteals (lymphatics of the small intestine) as chyle.

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.

Question 1

Which of the following is an endothelial smooth muscle relaxing factor?

Accepted Answer

Nitric oxide

Answer

Angiotensin

Answer

Dopamine

Answer

Vasopressin

Question 2

Afterload is best determined by?

Accepted Answer

Peripheral resistance

Answer

End diastolic volume

Answer

End systolic volume

Answer

Compliance

Question 3

Cardiac contractility is inhibited by which of the following factors?

Accepted Answer

Decreased phosphate (↓PO4)

Answer

Digitalis use

Answer

Respiratory acidosis

Answer

Metabolic alkalosis

Question 4

All of the following statements are false about stroke volume EXCEPT:

Accepted Answer

Decreases with an increase in heart rate

Answer

Determined by afterload

Answer

Determined by preload (pre-diastolic volume)

Answer

Increases with an increase in heart rate

Question 5

All of the following statements are false EXCEPT:

Accepted Answer

The left ventricle does more work than the right ventricle.

Answer

The right ventricle does more work than the left ventricle.

Answer

Both ventricles do equal work.

Answer

Maximum ventricular filling occurs during isovolumetric contraction.

Question 6

During the Valsalva maneuver, impaired heart rate changes are seen in which condition?

Accepted Answer

Autonomic insufficiency

Answer

Homer's syndrome

Answer

Vestibular dysfunction

Answer

Cephalic ischemia

Question 7

Pressure on the carotid sinus causes which of the following?

Accepted Answer

Reflex bradycardia

Answer

Hyperapnea

Answer

Tachycardia

Answer

Dyspnea

Question 8

What is the approximate rate of lymph flow in the human body?

Accepted Answer

120 ml/hr

Answer

10 ml/hr

Answer

20 ml/hr

Answer

50 ml/hr

Question 9

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 10

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

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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