Cardiovascular System Practice Questions

Q: Sinus bradycardia is seen in:

Athletes. **Explanation:** **Sinus bradycardia** is defined as a heart rate of less than 60 beats per minute originating from the SA node. **Why Athletes is the correct answer:** In highly trained athletes, chronic aerobic conditioning leads to **increased vagal (parasympathetic) tone** and a simultaneous decrease in sympathetic drive at rest. Additionally, exercise induces physiological cardiac hypertrophy, which increases the **stroke volume**. According to the formula *Cardiac Output = Stroke Volume × Heart Rate*, a higher stroke volume allows the heart to maintain the required cardiac output at a lower resting heart rate. This is a physiological adaptation known as "Athletic Heart Syndrome." **Why the other options are incorrect:** * **Exercise:** During exercise, the body’s demand for oxygen increases, leading to sympathetic activation and withdrawal of vagal tone. This results in **sinus tachycardia**, not bradycardia. * **Thyrotoxicosis:** Excess thyroid hormones (T3/T4) increase the expression of beta-1 adrenergic receptors in the heart and have direct chronotropic effects, leading to **tachycardia** and often atrial fibrillation. * **Beta adrenoceptor agonists:** These drugs (e.g., Adrenaline, Isoprenaline) stimulate beta-1 receptors in the SA node, increasing the rate of phase 4 depolarization, which causes **tachycardia**. (Note: Beta-blockers/antagonists cause bradycardia). **High-Yield NEET-PG Pearls:** * **Other causes of Sinus Bradycardia:** Hypothyroidism, Hypothermia, Obstructive Jaundice (bile salts act on the SA node), Raised Intracranial Pressure (Cushing’s reflex), and drugs like Digoxin or Beta-blockers. * **Bainbridge Reflex:** An increase in right atrial pressure leads to an increase in heart rate (tachycardia) to pump the excess blood. * **Oculocardiac Reflex:** Pressure on the eyeball can trigger profound bradycardia via the trigeminal (afferent) and vagus (efferent) nerves.

Q: Clamping of the carotid arteries below the carotid sinus is likely to produce what?

Increase in vasomotor center activity. **Explanation:** The carotid sinus, located at the bifurcation of the common carotid artery, contains **baroreceptors** (stretch receptors) that monitor arterial blood pressure. These receptors send inhibitory signals via the **Hering’s nerve** (branch of Glossopharyngeal nerve, CN IX) to the Nucleus Tractus Solitarius (NTS) in the medulla. **Why Option A is correct:** When the carotid arteries are clamped **below** the sinus, blood flow to the sinus is cut off. This leads to a **decrease in transmural pressure** within the carotid sinus. The baroreceptors perceive this as a drop in systemic blood pressure. Consequently, the rate of afferent firing decreases, leading to "disinhibition" of the **Vasomotor Center (VMC)**. The VMC then increases sympathetic outflow, resulting in peripheral vasoconstriction, increased heart rate, and a rise in systemic blood pressure (the **Carotid Sinus Reflex**). **Why other options are incorrect:** * **Option B:** Clamping reduces pressure in the sinus; therefore, the discharge rate of afferent nerves **decreases**, not increases. * **Option C:** The reflex response to perceived hypotension is an **increase** in heart rate (tachycardia) and blood pressure (hypertension) to compensate. * **Option D:** Baroreceptor adaptation refers to the resetting of receptors to a higher baseline in chronic hypertension; it is not an acute response to clamping. **High-Yield NEET-PG Pearls:** * **Afferent Pathway:** Carotid Sinus → CN IX; Aortic Arch → CN X (Vagus). * **Location:** Carotid sinus is a dilatation of the **Internal Carotid Artery** just above the bifurcation. * **Clinical Correlation:** Carotid sinus massage mimics high pressure, stimulating the baroreceptors to increase vagal tone, which can terminate Paroxysmal Supraventricular Tachycardia (PSVT).

Q: Pressure diuresis lowers arterial pressure because it?

Lowers blood volume. **Explanation:** **Pressure Diuresis** is a key mechanism of the renal-body fluid feedback system for long-term arterial pressure control. 1. **Why Option A is correct:** When arterial pressure rises, the kidneys increase the excretion of water (**pressure diuresis**) and sodium (**pressure natriuresis**). This occurs because the increased pressure directly increases the glomerular filtration rate (GFR) and inhibits tubular reabsorption of water and sodium. The resulting loss of fluid **lowers the extracellular fluid volume and blood volume**, which reduces venous return and cardiac output, ultimately bringing the arterial pressure back toward the normal set point. 2. **Why other options are incorrect:** * **Option B:** While high pressure does eventually suppress renin release, the primary physical mechanism by which pressure diuresis *lowers* pressure is the direct reduction of fluid volume. * **Option C:** Pressure diuresis affects the "volume" component of the blood pressure equation ($BP = CO \times SVR$), not the systemic vascular resistance directly. * **Option D:** Renal vasodilation may occur as an autoregulatory response to high pressure, but it is a *cause* or a concomitant finding, not the mechanism by which diuresis lowers systemic arterial pressure. **High-Yield Clinical Pearls for NEET-PG:** * **Guyton’s Curve:** The relationship between arterial pressure and urinary output is nearly linear; a slight increase in BP can cause a 2-3 fold increase in urine output. * **Pressure Natriuresis:** This refers specifically to the increased excretion of sodium in response to elevated pressure; it usually occurs alongside pressure diuresis. * **Chronic vs. Acute:** The renal-body fluid mechanism is the most potent **long-term** regulator of blood pressure, unlike the baroreceptor reflex, which is for short-term/acute changes.

Q: Which of the following statements is NOT true about a shunt vessel?

It is not under autonomic control. ### Explanation **Shunt vessels**, also known as **Arteriovenous (AV) Anastomoses**, are direct communications between small arteries and veins that bypass the capillary bed [2]. #### Why Option D is the Correct Answer (The "Not True" Statement) Shunt vessels are **highly regulated by the autonomic nervous system**, specifically the sympathetic division [1]. In the skin, sympathetic stimulation causes these vessels to constrict, diverting blood to the capillary bed or deeper tissues [2]. Therefore, the statement that they are "not under autonomic control" is false [3]. #### Analysis of Other Options * **Option A (Temperature Regulation):** This is a primary function. AV shunts are abundant in the skin of the nose, lips, ears, and fingertips [2]. When the body is cold, shunts constrict to conserve heat; when hot, they dilate to allow rapid blood flow near the surface for heat dissipation. * **Option B (Direct Communication):** This is the anatomical definition of a shunt vessel. It allows blood to flow from the arterial side to the venous side without passing through the high-resistance capillary network [2]. * **Option C (Local Mediators):** While primarily under autonomic control, shunt vessels also respond to local metabolic factors and inflammatory mediators (like histamine or bradykinin), which can alter their diameter [3]. #### NEET-PG High-Yield Pearls * **Glomus Body:** A specialized form of AV anastomosis found in the dermis of the skin (especially nail beds), involved in thermoregulation. A "Glomus tumor" is a painful benign neoplasm arising from these structures. * **Location:** AV shunts are absent in the brain and cardiac tissue (where constant capillary exchange is vital) but are numerous in the skin and gastrointestinal mucosa [2]. * **Function:** They regulate peripheral resistance and blood pressure in addition to thermoregulation.

Q: Elasticity of heart muscle mainly depends on which protein?

Titin. **Explanation:** The correct answer is **Titin** (also known as connectin). **Why Titin is correct:** Titin is the largest known protein in the human body and acts as a molecular spring within the sarcomere. It extends from the Z-disc to the M-line, anchoring the thick filaments (myosin) in the center. Its primary physiological role is to provide **passive elasticity** and stiffness to the cardiac muscle. During diastole, as the heart fills with blood, titin molecules stretch; during systole, they recoil, contributing to the Frank-Starling mechanism by ensuring the sarcomere returns to its original length. **Why the other options are incorrect:** * **Myosin (Option A):** This is the primary protein of the **thick filament** responsible for the "power stroke" and active contraction (force generation), not passive elasticity. * **Actin (Option B):** This is the primary protein of the **thin filament**. It provides the binding sites for myosin heads during contraction but does not possess elastic properties. * **Troponin (Option D):** This is a regulatory protein complex (T, I, and C) that modulates the interaction between actin and myosin in response to calcium levels. It does not contribute to the structural elasticity of the muscle. **High-Yield NEET-PG Pearls:** * **Frank-Starling Law:** Titin is a major determinant of the length-tension relationship in the heart. * **Clinical Correlation:** Mutations in the *TTN* gene (encoding Titin) are the most common genetic cause of **Dilated Cardiomyopathy (DCM)**. * **Stiffness:** In Diastolic Heart Failure (HFpEF), alterations in titin phosphorylation can lead to increased myocardial stiffness. * **Size:** Remember Titin as the "giant" protein of the sarcomere.

Q: Which phase of the cardiac cycle follows immediately after the beginning of the QRS wave?

Isovolumic contraction. **Explanation:** The cardiac cycle is a sequence of electrical and mechanical events. To answer this question, one must correlate the **Electrocardiogram (ECG)** with the mechanical phases of the heart. **Why Isovolumic Contraction is Correct:** The **QRS complex** represents **ventricular depolarization**. This electrical trigger leads to the onset of ventricular systole. The very first phase of ventricular systole is **isovolumic contraction**. During this phase, the ventricles begin to contract, causing intraventricular pressure to rise sharply. This pressure rise immediately closes the Atrioventricular (AV) valves (producing the **S1 heart sound**). Since the semilunar valves are not yet open, the ventricle contracts as a closed chamber with no change in volume. **Analysis of Incorrect Options:** * **Atrial Systole:** This corresponds to the **P wave** (atrial depolarization) on the ECG. It occurs before the QRS complex. * **Diastasis:** This is the phase of slow ventricular filling during diastole. It occurs long after the T wave and before the next P wave. * **Isovolumic Relaxation:** This occurs at the beginning of ventricular diastole, immediately following the closure of the semilunar valves (associated with the end of the **T wave**). **High-Yield NEET-PG Pearls:** * **S1 Heart Sound:** Occurs at the beginning of isovolumic contraction (just after the R wave peak). * **S2 Heart Sound:** Occurs at the beginning of isovolumic relaxation. * **Maximum Oxygen Consumption:** The heart consumes the most oxygen during the **isovolumic contraction phase** because it is generating high pressure against closed valves. * **c-wave (JVP):** Corresponds to isovolumic contraction (bulging of the tricuspid valve into the right atrium).

Q: Cardiac muscle contraction is primarily dependent on which of the following?

Extracellular Ca2+. **Explanation:** The correct answer is **Extracellular Ca2+** because of the unique mechanism of **Calcium-Induced Calcium Release (CICR)** in cardiac muscle. 1. **Why Extracellular Ca2+ is correct:** Unlike skeletal muscle, which can contract without external calcium, cardiac muscle contraction is highly dependent on the influx of extracellular calcium. During the plateau phase (Phase 2) of the cardiac action potential, **L-type calcium channels (Dihydropyridine receptors)** open, allowing extracellular Ca2+ to enter the cell. This "trigger calcium" then binds to **Ryanodine receptors (RyR2)** on the Sarcoplasmic Reticulum (SR), causing a massive release of stored calcium into the sarcoplasm. Without the initial influx of extracellular Ca2+, the SR cannot release its stores, and contraction cannot occur. 2. **Why the other options are incorrect:** * **Sarcoplasmic Ca2+:** While this is the immediate source for cross-bridge cycling, its release is *dependent* on the prior entry of extracellular calcium. Therefore, the primary dependency lies with the external source. * **Extracellular/Intracellular Na+:** Sodium ions are responsible for the rapid depolarization (Phase 0) of the action potential but do not directly initiate the contractile machinery (actin-myosin interaction). **Clinical Pearls & High-Yield Facts for NEET-PG:** * **Inotropy:** Drugs like **Digitalis** increase cardiac contractility by indirectly increasing intracellular Ca2+ (by inhibiting the Na+/K+ ATPase pump, which slows the Na+/Ca2+ exchanger). * **Calcium Channel Blockers (CCBs):** Verapamil and Diltiazem act on L-type channels, reducing the "trigger" calcium and exerting a negative inotropic effect. * **Skeletal vs. Cardiac:** Skeletal muscle uses **electromechanical coupling** (direct physical link between receptors), whereas cardiac muscle uses **electrochemical coupling** (CICR).

Question 1

Sinus bradycardia is seen in:

Accepted Answer

Athletes

Answer

Exercise

Answer

Thyrotoxicosis

Answer

Beta adrenoceptor agonist

Question 2

Clamping of the carotid arteries below the carotid sinus is likely to produce what?

Accepted Answer

Increase in vasomotor center activity

Answer

Increase in discharge of carotid sinus afferent nerves

Answer

Decreased heart rate and blood pressure

Answer

Baroreceptor adaptation

Question 3

Pressure diuresis lowers arterial pressure because it?

Accepted Answer

Lowers blood volume

Answer

Lowers renal release of renin

Answer

Lowers systemic vascular resistance

Answer

Causes renal vasodilation

Question 4

As atmospheric pressure is raised and lowered during the course of a day, blood flow through the brain would be expected to?

Accepted Answer

Remain constant because cerebral vascular resistance changes in the same direction as atmospheric pressure.

Answer

Change in the same direction as the atmospheric blood pressure because of the limited autoregulatory ability of the cerebral vessels.

Answer

Change in a direction opposite the change in mean atmospheric pressure.

Answer

Fluctuate widely, as both atmospheric pressure and brain neural activity status change.

Question 5

Which of the following statements is NOT true about a shunt vessel?

Accepted Answer

It is not under autonomic control

Answer

It controls temperature regulation

Answer

It is a direct communication between an artery and a vein

Answer

It is under control of local mediators

Question 6

Elasticity of heart muscle mainly depends on which protein?

Accepted Answer

Titin

Answer

Myosin

Answer

Actin

Answer

Troponin

Question 7

Which phase of the cardiac cycle follows immediately after the beginning of the QRS wave?

Accepted Answer

Isovolumic contraction

Answer

Isovolumic relaxation

Answer

Atrial systole

Answer

Diastasis

Question 8

Delayed afterdepolarization implies what?

Accepted Answer

All of the above

Answer

Increased intracellular Ca2+

Answer

Excessive catecholamines

Answer

Digitalis toxicity

Question 9

Which of the following statements about Reynolds' number is incorrect?

Accepted Answer

A Reynolds' number greater than 2500 suggests turbulent blood flow.

Answer

Reynolds' number predicts the likelihood of turbulent flow.

Answer

Reynolds' number is calculated as ρDV / η.

Answer

A Reynolds' number less than 2000 suggests laminar blood flow.

Question 10

Cardiac muscle contraction is primarily dependent on which of the following?

Accepted Answer

Extracellular Ca2+

Answer

Sarcoplasmic Ca2+

Answer

Extracellular Na+

Answer

Intracellular Na+

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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