Cardiovascular System Practice Questions

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: A 60-year-old female with a history of hypertension presents with symptoms of left-sided heart failure. Which of the following physiological changes is most likely contributing to her symptoms?

Increased left ventricular preload. ***Increased left ventricular preload*** - In **left-sided heart failure**, the left ventricle's ability to pump blood effectively is compromised, leading to **blood backing up** into the left atrium and pulmonary circulation [1]. - This increased volume of blood returning to a failing ventricle results in **elevated left ventricular end-diastolic pressure and volume** (preload), contributing to pulmonary congestion and symptoms like dyspnea [2]. *Decreased systemic vascular resistance* - **Decreased systemic vascular resistance (SVR)** would typically lead to a reduction in afterload, making it easier for the heart to pump blood, rather than causing left-sided heart failure [2]. - While medications for heart failure might aim to decrease SVR, it is not a primary physiological cause of the failure itself. *Decreased pulmonary artery pressure* - **Decreased pulmonary artery pressure** would indicate less resistance in the pulmonary circulation, which would alleviate symptoms of left-sided heart failure, not contribute to them. - Left-sided heart failure typically causes **increased pulmonary artery pressure** due to back-up of blood [1]. *Increased right atrial pressure* - **Increased right atrial pressure** is a hallmark of **right-sided heart failure**, indicating blood congestion in the systemic circulation [1]. - While left-sided failure can eventually lead to right-sided failure, high right atrial pressure isn't the primary physiological change contributing to *left-sided* heart failure symptoms.

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: 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: During vigorous exercise, a person experiences rapid breathing and an increased heart rate. Which of the following best describes the physiological mechanism behind the increase in heart rate?

Increased sympathetic nervous system activity. ***Increased sympathetic nervous system activity*** - During vigorous exercise, the body requires more oxygen and nutrient delivery to muscles, which is primarily mediated by the **sympathetic nervous system**. - **Sympathetic stimulation** leads to the release of **norepinephrine and epinephrine**, which bind to beta-1 receptors in the heart, increasing heart rate and contractility. *Increased vagal tone* - **Vagal tone** is associated with the **parasympathetic nervous system**, which generally acts to decrease heart rate. - An increase in vagal tone would result in a **slower heart rate**, opposite to what is observed during vigorous exercise. *Increased activity of the chemoreceptors* - **Chemoreceptors** (central and peripheral) sense changes in blood O2, CO2, and pH, primarily affecting respiration. - While they can indirectly influence heart rate, their direct role is to regulate **breathing rate and depth** to maintain blood gas homeostasis. *Increased activity of the baroreceptors* - **Baroreceptors** are stretch receptors located in the carotid sinuses and aortic arch, responsible for sensing changes in **blood pressure**. - An increase in their activity typically leads to a **decrease in heart rate** to lower elevated blood pressure, which is usually not the primary response during exercise.

Q: How does moderate hyperkalemia primarily affect the resting membrane potential and excitability of cardiac muscle cells?

Decreased excitability due to decreased membrane potential. ***Decreased excitability due to decreased membrane potential*** - Moderate hyperkalemia causes a **decrease (depolarization)** of the **resting membrane potential**, making it less negative. - While initially this might seem to increase excitability, the sustained depolarization inactivates **voltage-gated sodium channels**, thereby *decreasing overall excitability* and slowing conduction velocity. *Increased excitability due to decreased membrane potential* - Although moderate hyperkalemia does cause a **decreased resting membrane potential (depolarization)**, this initial effect does not lead to *increased excitability* in the long term for cardiac muscle. - The sustained depolarization leads to the *inactivation of fast sodium channels*, preventing further action potentials from firing efficiently. *Increased excitability due to increased membrane potential* - This option is incorrect because hyperkalemia causes a *decrease* (depolarization), not an increase, in the **resting membrane potential**. - Additionally, sustained depolarization reduces, rather than increases, excitability in cardiac cells by inactivating sodium channels. *Decreased excitability due to increased membrane potential* - This is incorrect because hyperkalemia results in a *decrease* in the **resting membrane potential** (makes it less negative), not an increase. - While it correctly states decreased excitability, the reasoning for the membrane potential change is flawed.

Q: Cerebral blood flow is regulated by all of the following except:

Calcium ions. ***Calcium ions*** - While **calcium ions (Ca²⁺)** are mechanistically essential for vascular smooth muscle contraction and relaxation, they are **not considered a primary regulatory signal** for cerebral blood flow (CBF) in the same way as the other factors listed. - Ca²⁺ acts as an **intracellular second messenger** that mediates the effects of other regulatory factors (like PCO2, K⁺, and vasoactive substances), rather than being a direct extracellular regulatory signal itself. - The question refers to primary regulatory factors that directly modulate CBF, not the intracellular mechanisms by which vascular smooth muscle responds. *Blood pressure* - **Cerebral autoregulation** maintains relatively constant CBF despite changes in **mean arterial pressure (MAP)** between approximately 60-150 mmHg. - Blood pressure is a **key regulatory factor** - when MAP falls below or exceeds this range, CBF becomes pressure-dependent. - This protective mechanism prevents cerebral ischemia or hyperemia with systemic blood pressure fluctuations. *Arterial PCO2* - **Arterial partial pressure of carbon dioxide (PaCO2)** is one of the **most potent direct regulators** of CBF. - **Hypercapnia** (increased PaCO2) causes cerebral vasodilation and increased CBF (approximately 1-2 mL/100g/min increase per 1 mmHg rise in PaCO2). - **Hypocapnia** (decreased PaCO2) causes vasoconstriction and reduced CBF, utilized therapeutically in managing elevated intracranial pressure. *Potassium ions* - **Increased extracellular K⁺** in the perivascular space causes **direct vasodilation** of cerebral arterioles. - This mechanism is crucial for **neurovascular coupling** (functional hyperemia) - when neurons are active, they release K⁺, which dilates nearby vessels to increase local blood flow. - K⁺-mediated vasodilation helps match cerebral perfusion to metabolic demand during neuronal activity.

Q: What is the PRIMARY vascular function of PGI2 (prostacyclin)?

Inhibits platelet aggregation and causes vasodilation. ***Inhibits platelet aggregation and causes vasodilation*** - **PGI2 (prostacyclin)** is a potent **vasodilator** that relaxes smooth muscle in blood vessels, increasing blood flow. - It also effectively **inhibits platelet aggregation**, preventing the formation of blood clots. *Promotes platelet aggregation and causes vasoconstriction* - This describes the primary actions of **thromboxane A2 (TXA2)**, not PGI2. - TXA2 is produced by platelets and plays a key role in **hemostasis** by constricting blood vessels and promoting platelet clumping. *Acts primarily as a bronchoconstrictor* - While some prostaglandins can affect bronchial tone, **PGI2's primary vascular role** is vasodilation and anti-aggregation. - **Leukotrienes** and certain **prostaglandins (e.g., PGD2, PGF2α)** are more classically associated with bronchoconstriction. *Stimulates inflammatory cell chemotaxis* - This is primarily a function of other inflammatory mediators such as **leukotriene B4 (LTB4)** and **C5a anaphylatoxin**. - While other eicosanoids can indirectly influence inflammation, **PGI2's main actions** are vascular and anti-platelet.

Q: Closure of patent ductus arteriosus is stimulated by?

Increase in O2 tension at birth. ***Increase in O2 tension at birth*** - The **patent ductus arteriosus (PDA)** remains open during fetal life due to low oxygen tension and elevated **prostaglandin E2** levels. - At birth, the first breath significantly increases **pulmonary blood flow** and **arterial oxygen tension**, leading to constriction and functional closure of the PDA. *Prostaglandin F2a* - While prostaglandins play a crucial role in vascular tone, **prostaglandin F2a** is not the primary mediator for PDA closure. - **Prostaglandin E2** is primarily responsible for keeping the ductus arteriosus open in utero. *Cyclooxygenase* - **Cyclooxygenase (COX)** is an enzyme involved in the synthesis of prostaglandins. - While inhibitors of COX (e.g., indomethacin) can induce PDA closure by reducing prostaglandin synthesis, COX itself does not directly stimulate closure. *Hypercarbia* - **Hypercarbia** (elevated CO2 levels) is typically associated with **vasodilation**, particularly in the cerebral circulation, and would not promote PDA closure. - It does not directly impact the mechanisms responsible for the constriction of the ductus arteriosus.

Q: What is the purpose of the square wave seen in an ECG recording?

Used for standardization of ECG. ***Used for standardization of ECG*** - The **square wave** at the beginning of an ECG tracing is a **calibration signal**, typically 1 mV in amplitude and 0.2 seconds in duration. - It ensures that the ECG machine is accurately recording the electrical activity, allowing for proper measurement of subsequent waveforms. *Indicates atrial depolarization* - **Atrial depolarization** is represented by the **P wave** on the ECG, which is a small, rounded wave preceding the QRS complex. - The square wave serves a technical purpose for calibration, not a physiological one related to cardiac electrical activity. *Indicates ventricular depolarization* - **Ventricular depolarization** is represented by the **QRS complex**, which is a sharp, prominent deflection following the P wave. - This complex reflects the rapid electrical activation of the ventricles, very different from the calibration square wave. *Indicates ventricular repolarization* - **Ventricular repolarization** is represented by the **T wave**, which is typically a rounded wave following the QRS complex. - This physiological event is distinct from the initial square wave, which is an artifact generated by the ECG device for calibration.

Question 1

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 2

A 60-year-old female with a history of hypertension presents with symptoms of left-sided heart failure. Which of the following physiological changes is most likely contributing to her symptoms?

Accepted Answer

Increased left ventricular preload

Answer

Decreased systemic vascular resistance

Answer

Decreased pulmonary artery pressure

Answer

Increased right atrial pressure

Question 3

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

Accepted Answer

Baroreceptors

Answer

Chemoreceptors

Answer

Nociceptors

Answer

Thermoreceptors

Question 4

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 5

During vigorous exercise, a person experiences rapid breathing and an increased heart rate. Which of the following best describes the physiological mechanism behind the increase in heart rate?

Accepted Answer

Increased sympathetic nervous system activity

Answer

Increased vagal tone

Answer

Increased activity of the baroreceptors

Answer

Increased activity of the chemoreceptors

Question 6

How does moderate hyperkalemia primarily affect the resting membrane potential and excitability of cardiac muscle cells?

Accepted Answer

Decreased excitability due to decreased membrane potential

Answer

Increased excitability due to increased membrane potential

Answer

Increased excitability due to decreased membrane potential

Answer

Decreased excitability due to increased membrane potential

Question 7

Cerebral blood flow is regulated by all of the following except:

Accepted Answer

Calcium ions

Answer

Blood pressure

Answer

Arterial PCO2

Answer

Potassium ions

Question 8

What is the PRIMARY vascular function of PGI2 (prostacyclin)?

Accepted Answer

Inhibits platelet aggregation and causes vasodilation

Answer

Promotes platelet aggregation and causes vasoconstriction

Answer

Acts primarily as a bronchoconstrictor

Answer

Stimulates inflammatory cell chemotaxis

Question 9

Closure of patent ductus arteriosus is stimulated by?

Accepted Answer

Increase in O2 tension at birth

Answer

Prostaglandin F2a

Answer

Hypercarbia

Answer

Cyclooxygenase

Question 10

What is the purpose of the square wave seen in an ECG recording?

Accepted Answer

Used for standardization of ECG

Answer

Indicates atrial depolarization

Answer

Indicates ventricular depolarization

Answer

Indicates ventricular repolarization

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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