Cardiovascular System Practice Questions

Q: During which phase of the cardiac cycle does the majority of ventricular filling take place?

Rapid filling. ***Rapid filling*** - **Ventricular filling** occurs during diastole in multiple phases, but the **rapid filling phase** (early diastole) is when approximately **75% of ventricular filling** occurs due to the maximal pressure gradient between atria and ventricles. - During this phase, the **atrioventricular (AV) valves** (mitral and tricuspid) are open, allowing blood to passively rush into the relaxing ventricles as they expand rapidly. - The remaining filling occurs during diastasis (slow filling) and atrial systole (~25%). *Isovolumetric contraction* - This phase occurs at the beginning of systole, where the ventricles contract, but all valves (AV and semilunar) are closed, resulting in a **rise in ventricular pressure** without a change in volume. - No blood enters or leaves the ventricles during isovolumetric contraction; therefore, **no ventricular filling occurs**. *Isovolumetric relaxation* - This phase occurs at the beginning of diastole, immediately after ejection, where the ventricles relax, but all valves are closed, resulting in a **fall in ventricular pressure** without a change in volume. - While it precedes ventricular filling, **no blood enters** the ventricles during this specific phase because the AV valves remain closed until ventricular pressure falls below atrial pressure. *Ejection* - The ejection phase is part of **ventricular systole**, where the semilunar valves open, and blood is actively pumped out of the ventricles into the aorta and pulmonary artery. - During ejection, the ventricles are emptying, not filling; therefore, **no ventricular filling occurs**.

Q: What is the primary source of calcium for cardiac muscle contraction?

Release from the sarcoplasmic reticulum. ***Release from the sarcoplasmic reticulum*** - The influx of extracellular calcium through **L-type calcium channels** triggers the release of a much larger amount of calcium from the **sarcoplasmic reticulum** via ryanodine receptors (RyRs) in a process called **calcium-induced calcium release (CICR)**. - This massive release of calcium from the sarcoplasmic reticulum is the **primary source** of intracellular calcium responsible for initiating myocyte contraction. - Approximately **70-90%** of the calcium needed for contraction comes from the SR, making it the predominant source. *Release from extracellular fluid* - While **extracellular calcium** influx is crucial for initiating the contraction, it serves as a trigger rather than the primary source of calcium needed for the actual muscle contraction. - The amount of calcium entering from the extracellular fluid is significantly less than the amount released from the sarcoplasmic reticulum. - This extracellular calcium entry accounts for only **10-30%** of total calcium during contraction. *Binding to troponin C* - **Calcium binding to troponin C** is the primary ACTION or mechanism of calcium, not its source. - While this is crucial for the excitation-contraction coupling cascade (leading to unmasking of actin-myosin binding sites), it describes what calcium does, not where it comes from. *Activation of calcium-calmodulin complex* - The **calcium-calmodulin complex** plays a more prominent regulatory role in **smooth muscle contraction** and other cellular processes. - In cardiac muscle, while calmodulin has some functions, it is not the primary source or mechanism by which calcium triggers contraction.

Q: Which ion is primarily responsible for the plateau phase of the cardiac action potential?

Calcium. **✓ Calcium (Correct Answer)** - The **influx of calcium ions (Ca²⁺)** through L-type calcium channels maintains the depolarized state during the **plateau phase (Phase 2)** of the cardiac action potential. - This sustained calcium influx balances the efflux of potassium ions, prolonging depolarization and preventing premature repolarization. - The plateau phase is crucial for adequate ventricular contraction and preventing tetany. *Sodium (Incorrect)* - **Sodium influx (Na⁺)** is primarily responsible for the rapid **depolarization phase (Phase 0)** of the cardiac action potential, causing a quick rise in membrane potential. - While essential for initiation, sodium channels rapidly inactivate by the time the plateau phase begins. - Sodium plays no significant role in maintaining the plateau. *Potassium (Incorrect)* - **Potassium efflux (K⁺)** through delayed rectifier potassium channels is responsible for the **repolarization phase (Phase 3)**, returning the membrane potential to its resting state. - During the plateau phase, potassium efflux is reduced (not the primary mechanism), which contributes to maintaining the plateau, but calcium influx is the primary driver. *Chloride (Incorrect)* - Chloride ions (Cl⁻) play a relatively **minor role** in the ventricular cardiac action potential compared to sodium, potassium, and calcium. - While chloride channels exist in cardiac cells, their contribution is not significant in maintaining the plateau phase.

Q: A 50-year-old man presents with severe hypotension after a myocardial infarction. Which of the following compensatory mechanisms is primarily mediated by the baroreceptor reflex?

Increased heart rate. ***Increased heart rate*** - The baroreceptor reflex detects a drop in blood pressure (due to hypotension) and responds by **increasing sympathetic outflow** to the heart. - This sympathetic activation directly leads to an **increased heart rate** and contractility to restore blood pressure. *Decreased renin release* - **Renin release** is typically increased in response to hypotension, via the juxtaglomerular apparatus, to activate the **renin-angiotensin-aldosterone system** (RAAS). - A decrease in renin release would further exacerbate hypotension, which is not a compensatory mechanism. *Vasodilation of peripheral vessels* - The baroreceptor reflex, in response to hypotension, aims to **increase peripheral vascular resistance** through vasoconstriction, not vasodilation. - **Vasodilation** would further reduce blood pressure and is directly counterproductive to compensating for hypotension. *Increased parasympathetic activity* - In response to hypotension, the baroreceptor reflex primarily **decreases parasympathetic activity** and increases sympathetic activity. - Increased parasympathetic activity would lead to a **decreased heart rate**, worsening the hypotensive state.

Q: Which of the following best describes the function of the hepatic portal vein?

Carries nutrient-rich blood from the GI tract to the liver. ***Carries nutrient-rich blood from the GI tract to the liver*** - The **hepatic portal vein** collects blood rich in absorbed nutrients (and toxins) from the gastrointestinal tract, spleen, and pancreas. - This **nutrient-rich blood** is then delivered to the liver for processing, metabolism, and detoxification before entering the systemic circulation. *Transports bile from the liver* - **Bile** is transported away from the liver by the **bile ducts**, which merge to form the common hepatic duct. - The hepatic portal vein carries blood *to* the liver, not bile *from* it. *Supplies oxygenated blood to the liver* - The **hepatic artery** is responsible for supplying oxygenated blood to the liver tissue, providing its metabolic needs. - The hepatic portal vein carries **deoxygenated blood** that is rich in nutrients and metabolic products. *Removes toxins from the liver* - While the liver **detoxifies** substances, the hepatic portal vein delivers these substances *to* the liver for processing. - Processed toxins and metabolic wastes are primarily excreted via **bile** or returned to the systemic circulation to be filtered by the kidneys.

Q: In a patient with hypovolemic shock, what is the expected initial compensatory mechanism?

Increased sympathetic activity. ***Increased sympathetic activity*** - In **hypovolemic shock**, the body's initial response to decreased blood volume and cardiac output is to activate the **sympathetic nervous system**. - This activation leads to the release of **catecholamines** (epinephrine and norepinephrine), causing **vasoconstriction**, increased heart rate, and increased myocardial contractility to maintain blood pressure and perfusion. *Increased venous return* - **Hypovolemic shock** is characterized by a **reduction in blood volume**, leading directly to a **decreased venous return** to the heart, not an increase. - Increased venous return would typically improve cardiac output, which is the opposite of what happens in initial hypovolemic shock. *Decreased systemic vascular resistance* - **Sympathetic activation** in hypovolemic shock primarily causes **vasoconstriction**, which leads to an **increase in systemic vascular resistance (SVR)** to divert blood to vital organs and maintain blood pressure. - Decreased SVR would further lower blood pressure, exacerbating the shock state. *Decreased heart rate* - A hallmark compensatory mechanism in **hypovolemic shock** is an **increase in heart rate** (tachycardia) to compensate for the reduced stroke volume and maintain cardiac output. - A decreased heart rate would worsen cardiac output and is not an initial compensatory mechanism.

Q: Which of the following statements about Reynolds number in physiology is MOST correct?

Reynolds number less than 2000 indicates laminar blood flow. **Reynolds number less than 2000 indicates laminar blood flow** - A **Reynolds number (Re)** below 2000 in a tube context, such as blood vessels, signifies **laminar flow**, where fluid particles move smoothly in parallel layers. - In **normal, healthy arteries**, blood flow is predominantly laminar, characterized by less resistance and efficient transport. *Reynolds number greater than 3000 indicates turbulent blood flow* - While a higher Reynolds number generally indicates turbulent flow, the transition from laminar to turbulent flow typically begins around an Re of 2000, and is generally fully turbulent at Re > 4000. - Beyond **an Re of 4000**, flow is unequivocally turbulent, characterized by chaotic, irregular fluid motion. *Reynolds number between 2000 and 3000 indicates transitional blood flow* - Reynolds numbers between 2000 and 4000 indicate a **transitional flow regime**, where the flow alternates between laminar and turbulent characteristics. - This phase represents an instability where minor disturbances can trigger turbulent patterns. *Reynolds number calculates the probability of turbulence* - The Reynolds number is a **dimensionless quantity** used to predict flow patterns, specifically whether flow will be laminar or turbulent, based on fluid properties, velocity, and characteristic length. - It is a **deterministic indicator** of flow type rather than a probability calculation.

Q: During which phase of the cardiac cycle does the majority of coronary blood flow to the myocardium take place?

Early diastole. ***Early diastole*** - During **early diastole**, immediately after **aortic valve closure**, the **left ventricle** relaxes, and intramyocardial pressure drops significantly, allowing the **coronary arteries** to be perfused readily. - The combination of **low myocardial compression** and a still relatively high **aortic diastolic pressure** creates an optimal pressure gradient for blood flow into the coronary circulation. - Approximately **70-80% of left coronary blood flow** occurs during diastole, with the peak flow in the early phase. *Systole* - During **systole**, the contraction of the **ventricular myocardium** compresses the intramural coronary arteries, significantly impeding blood flow, especially in the **left ventricle**. - **Aortic pressure** is highest during systole, but the mechanical compression outweighs this, reducing myocardial perfusion. *Late diastole* - While there is some **coronary flow** during late diastole, it is less than in early diastole because **venous return** and **ventricular filling** increase intraventricular pressure. - The **aortic pressure** also gradually declines towards the end of diastole, reducing the driving force for coronary perfusion compared to early diastole. *Isovolumetric contraction* - During **isovolumetric contraction**, the **ventricular muscle** tenses but does not yet eject blood, leading to a rapid increase in **intraventricular pressure**. - This high intramyocardial pressure severely **compresses the coronary vessels**, virtually stopping blood flow to the **myocardium** during this brief phase.

Q: The immediate response of the body to acute hypervolemia is mediated by which receptors?

Baroreceptors. ***Correct: Baroreceptors*** - Baroreceptors are **stretch-sensitive mechanoreceptors** located in the carotid sinuses and aortic arch that detect changes in blood pressure and blood volume. - In acute hypervolemia, the increased blood volume leads to **increased central venous pressure and arterial pressure**, which stimulates these baroreceptors. - This triggers an **immediate compensatory response** including decreased sympathetic activity, increased parasympathetic activity, and decreased vasopressin release to reduce blood volume and pressure. *Incorrect: Chemoreceptors* - Chemoreceptors primarily detect changes in **blood pH, oxygen (pO2), and carbon dioxide (pCO2)** levels. - While they play a role in regulating respiration and can influence cardiovascular function, they are **not the primary immediate sensors for changes in blood volume**. *Incorrect: Nociceptors* - Nociceptors are **pain receptors** that respond to noxious stimuli, signaling potential tissue damage. - They are completely unrelated to the physiological regulation of blood volume or pressure in the context of hypervolemia. *Incorrect: Thermoreceptors* - Thermoreceptors detect changes in **temperature**, both internal and external. - They are involved in maintaining body temperature homeostasis and do not play any direct role in the immediate response to acute hypervolemia.

Q: Which heart chamber pumps oxygenated blood to the systemic circulation?

Left ventricle. ***Left ventricle*** - The **left ventricle** receives **oxygenated blood** from the left atrium and has the thickest muscular wall to pump this blood with high pressure into the **aorta** for distribution throughout the body. - Its powerful contractions are essential for maintaining systemic blood flow and delivering oxygen to all tissues. *Right atrium* - The right atrium receives **deoxygenated blood** from the systemic circulation via the **superior and inferior vena cavae**. - It pumps blood into the right ventricle, not into the systemic circulation. *Right ventricle* - The right ventricle pumps **deoxygenated blood** to the **pulmonary arteries** for oxygenation in the lungs. - Its function is limited to the **pulmonary circulation**, not the systemic circulation. *Left atrium* - The left atrium receives **oxygenated blood** from the lungs via the **pulmonary veins**. - It delivers blood to the left ventricle but does not pump directly into the systemic circulation.

Question 1

During which phase of the cardiac cycle does the majority of ventricular filling take place?

Accepted Answer

Rapid filling

Answer

Isovolumetric relaxation

Answer

Ejection

Answer

Isovolumetric contraction

Question 2

What is the primary source of calcium for cardiac muscle contraction?

Accepted Answer

Release from the sarcoplasmic reticulum

Answer

Release from extracellular fluid

Answer

Binding to troponin C

Answer

Activation of calcium-calmodulin complex

Question 3

Which ion is primarily responsible for the plateau phase of the cardiac action potential?

Accepted Answer

Calcium

Answer

Sodium

Answer

Potassium

Answer

Chloride

Question 4

A 50-year-old man presents with severe hypotension after a myocardial infarction. Which of the following compensatory mechanisms is primarily mediated by the baroreceptor reflex?

Accepted Answer

Increased heart rate

Answer

Decreased renin release

Answer

Vasodilation of peripheral vessels

Answer

Increased parasympathetic activity

Question 5

Which of the following best describes the function of the hepatic portal vein?

Accepted Answer

Carries nutrient-rich blood from the GI tract to the liver

Answer

Transports bile from the liver

Answer

Supplies oxygenated blood to the liver

Answer

Removes toxins from the liver

Question 6

In a patient with hypovolemic shock, what is the expected initial compensatory mechanism?

Accepted Answer

Increased sympathetic activity

Answer

Increased venous return

Answer

Decreased systemic vascular resistance

Answer

Decreased heart rate

Question 7

Which of the following statements about Reynolds number in physiology is MOST correct?

Accepted Answer

Reynolds number less than 2000 indicates laminar blood flow

Answer

Reynolds number greater than 3000 indicates turbulent blood flow

Answer

Reynolds number calculates the probability of turbulence

Answer

Reynolds number between 2000 and 4000 indicates transitional blood flow

Question 8

During which phase of the cardiac cycle does the majority of coronary blood flow to the myocardium take place?

Accepted Answer

Early diastole

Answer

Systole

Answer

Late diastole

Answer

Isovolumetric contraction

Question 9

The immediate response of the body to acute hypervolemia is mediated by which receptors?

Accepted Answer

Baroreceptors

Answer

Chemoreceptors

Answer

Nociceptors

Answer

Thermoreceptors

Question 10

Which heart chamber pumps oxygenated blood to the systemic circulation?

Accepted Answer

Left ventricle

Answer

Right atrium

Answer

Right ventricle

Answer

Left atrium

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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