Cardiovascular System Practice Questions

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).

Q: What causes Korotkoff sounds?

Turbulent blood flow during occlusion of a vessel. **Explanation:** **Korotkoff sounds** are the sounds heard via stethoscope over the brachial artery during the measurement of blood pressure using a sphygmomanometer. **Why Option C is Correct:** Under normal conditions, blood flow in the arteries is **laminar** (silent). When a blood pressure cuff is inflated above systolic pressure, the artery is completely occluded. As the cuff pressure is gradually released to just below systolic pressure, blood begins to spurt through the partially constricted vessel. This high-velocity flow through a narrowed opening creates **turbulence**, which produces the audible vibrations known as Korotkoff sounds. **Analysis of Incorrect Options:** * **Option A:** Laminar flow is streamlined and silent; it does not produce sound. Korotkoff sounds occur because the cuff *disrupts* laminar flow. * **Option B:** Closure of the aortic valve produces the **S2 (second heart sound)**, heard over the precordium, not the peripheral Korotkoff sounds. * **Option D:** In a healthy individual, no sound is heard over a peripheral artery without cuff application because the flow is naturally laminar. **High-Yield NEET-PG Pearls:** * **Phase I:** The first appearance of clear tapping sounds (corresponds to **Systolic BP**). * **Phase V:** The point where sounds disappear completely (corresponds to **Diastolic BP** in adults). Note: In children or hyperdynamic states (e.g., pregnancy, thyrotoxicosis), Phase IV (muffling) is used for diastolic BP. * **Auscultatory Gap:** A silent interval between Phase I and Phase II; failure to recognize it can lead to underestimating systolic or overestimating diastolic pressure. It is common in hypertensive patients.

Question 1

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 2

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 3

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 4

Elasticity of heart muscle mainly depends on which protein?

Accepted Answer

Titin

Answer

Myosin

Answer

Actin

Answer

Troponin

Question 5

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 6

Delayed afterdepolarization implies what?

Accepted Answer

All of the above

Answer

Increased intracellular Ca2+

Answer

Excessive catecholamines

Answer

Digitalis toxicity

Question 7

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 8

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

Accepted Answer

Extracellular Ca2+

Answer

Sarcoplasmic Ca2+

Answer

Extracellular Na+

Answer

Intracellular Na+

Question 9

What causes Korotkoff sounds?

Accepted Answer

Turbulent blood flow during occlusion of a vessel

Answer

Increased laminar flow on application of pressure

Answer

Closure of aortic valve in diastole

Answer

Normal sound existing even without the application of a cuff

Question 10

Clamping of the carotid arteries above the carotid sinus results in what physiological changes?

Accepted Answer

Decrease in blood pressure and decrease in heart rate

Answer

Increase in blood pressure and increase in heart rate

Answer

Increase in blood pressure and decrease in heart rate

Answer

Decrease in blood pressure and increase in heart rate

Cardiovascular System — MCQs

Cardiovascular System — MCQs

On this page

Practice by Chapter

Want unlimited practice?