Cardiovascular System Practice Questions

Q: The ST Segment of an ECG corresponds to which phase of the action potential?

Plateau phase. ***Plateau phase*** - The **ST segment** of the ECG represents the period when the ventricles are completely depolarized and corresponds to the **plateau phase (phase 2)** of the ventricular myocardial action potential. - During this phase, there is a balance between **calcium influx** and **potassium efflux**, maintaining the depolarized state and contributing to the sustained contraction of the ventricles. *Rapid depolarization* - This phase, represented by the **QRS complex** on the ECG, signifies the rapid influx of sodium ions into the ventricular cells. - It corresponds to **phase 0** of the action potential, where there is a sharp upstroke. *Rapid repolarization* - This corresponds to **phase 3** of the ventricular action potential, where potassium ions rapidly exit the cell, leading to repolarization. - On the ECG, this phase is represented by the **T wave**. *Final repolarization* - This is **not a standard electrophysiological term** in cardiac action potential nomenclature. - The complete repolarization process is represented by the **T wave** (phase 3), which returns the ventricle to its resting potential (phase 4). - The term may cause confusion as it doesn't correspond to a specific phase or ECG component.

Q: Which of the following statements about the oculocardiac reflex is false?

It is mediated by oculomotor and vagus nerve. ***It is mediated by oculomotor and vagus nerve*** - The oculocardiac reflex (OCR) is classically mediated by the **trigeminal nerve (afferent)** and the **vagus nerve (efferent)**, not the oculomotor nerve. - Stimulation of the trigeminal sensory afferents from the eye leads to an efferent vagal response, causing a decrease in heart rate. *It is mediated by trigeminal and vagus nerve.* - This statement accurately describes the neural pathways involved in the oculocardiac reflex, where the **trigeminal nerve acts as the afferent limb** and the **vagus nerve acts as the efferent limb**. - Stimulation of ocular structures activates trigeminal nerve endings, which transmit signals to the brainstem, leading to vagal stimulation and subsequent cardiac effects. *Reflex is more sensitive in neonates* - The oculocardiac reflex is indeed more pronounced and easily triggered in **neonates and young children** due to their relatively immature autonomic nervous system. - This increased sensitivity makes them more susceptible to **bradycardia** during ophthalmic procedures. *It is characterized by bradycardia following traction on extra- ocular muscles* - The classic manifestation of the oculocardiac reflex is **bradycardia** (slowing of the heart rate) in response to stimuli such as pressure on the eyeball or traction on the extraocular muscles. - Other possible manifestations include **arrhythmias**, **asystole**, and hypotension, although bradycardia is the most common.

Q: Cerebral blood flow is most directly increased by?

Increase in PCO2. ***Increase in PCO2*** - An increase in **arterial PCO2** (partial pressure of carbon dioxide) causes **cerebral vasodilation**, leading to a direct increase in cerebral blood flow. - This is a potent regulatory mechanism to ensure adequate **carbon dioxide removal** and **oxygen supply** to the brain. *Increase in PO2* - An increase in **arterial PO2** (partial pressure of oxygen) causes **mild cerebral vasoconstriction**, which would tend to decrease cerebral blood flow, not increase it. - Cerebral blood flow is generally **less sensitive** to changes in PO2 within the normal range compared to PCO2. *Decrease metabolic rate* - A decrease in the brain's **metabolic rate** would typically lead to a **decrease in local demand** for oxygen and nutrients, resulting in **decreased cerebral blood flow**. - Cerebral blood flow is intrinsically linked to the metabolic needs of brain tissue. *Increase in metabolic rate* - An increase in the brain's **metabolic rate** would lead to an **increase in demand** for oxygen and glucose, which in turn causes **vasodilation** and an increase in cerebral blood flow. - However, this is an indirect effect, whereas an increase in PCO2 directly causes vasodilation.

Q: Which of the following statements is true about coronary circulation?

Major flow during diastole. ***Major flow during diastole*** - The **coronary arteries** are compressed during **systole** by the contracting myocardium, significantly reducing blood flow to the heart muscle. - During **diastole**, the myocardium relaxes, allowing the coronary arteries to open fully and deliver the majority (70-80%) of oxygenated blood to the heart. - This is the most distinctive feature of coronary circulation. *Flow rate is approximately 500 ml/min* - The typical **coronary blood flow** at rest is approximately **225-250 ml/min** (about 5% of cardiac output at rest). - 500 ml/min is significantly higher than normal resting coronary flow and would represent a pathological or high-demand state. *Uniform flow during full cardiac cycle* - **Coronary blood flow** is highly variable (phasic) throughout the cardiac cycle, being significantly higher during **diastole** and much lower during **systole**. - This non-uniform flow is a unique characteristic of coronary circulation due to mechanical compression from myocardial contraction. *All of the above* - Not all statements are correct, as the flow rate value is incorrect and flow is non-uniform throughout the cardiac cycle. - The **major flow during diastole** is the most accurate and physiologically important statement regarding coronary circulation.

Q: Where are the stretch receptors located in the left atrium?

Entrance of the pulmonary veins. ***Entrance of the pulmonary veins*** - **Stretch receptors** are mechanoreceptors that detect changes in pressure and volume. In the left atrium, they are primarily located at the **junction of the pulmonary veins and the left atrium** [1]. - These receptors play a crucial role in the **Bainbridge reflex** and the release of **atrial natriuretic peptide (ANP)** in response to increased blood volume [1]. *Atrioventricular septum* - The **atrioventricular septum** separates the atria from the ventricles and primarily contains components of the **cardiac conduction system**, such as the AV node and bundle of His [2]. - While it has specialized tissues, it is not the primary location for **stretch receptors** involved in volume sensing. *Septum between the atria* - The **interatrial septum** primarily separates the right and left atria. - Although it contains some myocardial cells, it is not the main site for **stretch receptors** responsible for monitoring left atrial volume. *None of the options* - This option is incorrect because the **entrance of the pulmonary veins** is indeed the primary location for stretch receptors in the left atrium [1].

Q: What is the mechanism by which M2 receptors mediate the inhibition of the heart by the vagus nerve?

Inhibition of adenylate cyclase. ***Inhibition of adenylate cyclase*** - M2 receptors are **Gαi-protein coupled receptors**, and their activation leads to the inhibition of **adenylate cyclase**. - This inhibition reduces the intracellular concentration of **cAMP**, which in turn decreases the activity of **protein kinase A (PKA)**, leading to a decrease in heart rate and contractility. - Additionally, M2 receptors activate **inwardly rectifying potassium channels (IKACh)**, which hyperpolarizes the cell membrane and further slows heart rate. *Activation of phospholipase C* - This mechanism is characteristic of **M1 and M3 muscarinic receptors (Gq-coupled)**, which activate phospholipase C, leading to increased IP3 and DAG. - This pathway is primarily involved in smooth muscle contraction and glandular secretion, not direct cardiac inhibition by M2 receptors. *Inhibition of cAMP breakdown* - Inhibition of **cAMP breakdown** would lead to an increase in cAMP levels, which would stimulate cardiac function. - This effect is mediated by drugs like **phosphodiesterase inhibitors**, which block the enzyme responsible for cAMP degradation, and is opposite to the effect of M2 receptor activation. *Opening of voltage-gated calcium channels* - Opening of voltage-gated calcium channels would **increase** calcium influx, leading to increased contractility and heart rate. - This is the mechanism of action of **sympathetic stimulation via β1-adrenergic receptors**, not parasympathetic M2 receptor activation, which has the opposite effect.

Q: How many phases are there in the action potential of cardiac muscles?

5 phases. ***5 phases*** - The cardiac myocyte action potential is classically described in **five phases** (phases 0, 1, 2, 3, and 4), which encompass depolarization, repolarization, and the resting state. - Each phase is characterized by specific ion channel activities leading to distinct electrical changes essential for proper cardiac function. *2 phases* - Action potentials in nerve cells typically follow a simpler two-phase model: **depolarization** and **repolarization**. - This model does not account for the additional plateau and resting phases characteristic of cardiac muscle cells. *3 phases* - Some simplified models might describe three phases (depolarization, repolarization, and a resting phase), but this still **omits specific nuances** of cardiac repolarization and the sustained plateau phase. - This simplification leaves out the early repolarization and the critical plateau phase (phase 2), which is vital for the prolonged contraction of the heart. *4 phases* - While some sources might refer to four phases, they typically combine certain repolarization steps or omit the distinct early repolarization phase. - This description would likely miss the **early, rapid repolarization phase (phase 1)**, understating the complex ion movements.

Q: Which of the following is the most immediate cardiovascular response to acute stress?

Increased heart rate. ***Increased heart rate*** - The **sympathetic nervous system** is immediately activated during acute stress, leading to a rapid release of **catecholamines** (epinephrine and norepinephrine). - These hormones directly stimulate the heart, causing an almost instantaneous increase in its **rate and contractility**. *Decreased heart rate* - A decreased heart rate, or **bradycardia**, is characteristic of a **parasympathetic response**, which aims to conserve energy and promote rest. - This is the opposite of the "fight-or-flight" response seen in acute stress. *Release of cortisol* - **Cortisol** is a steroid hormone released by the adrenal cortex as part of the **hypothalamic-pituitary-adrenal (HPA) axis** response to stress. - While important in the stress response, its release and effects are **slower** and more sustained compared to the immediate cardiovascular changes mediated by the sympathetic nervous system. *Decreased blood pressure* - Acute stress typically causes an **increase in blood pressure** due to **vasoconstriction** and increased cardiac output. - A decrease in blood pressure (hypotension) would be an atypical and potentially dangerous response to acute stress, often indicative of shock or other severe conditions.

Question 1

The ST Segment of an ECG corresponds to which phase of the action potential?

Accepted Answer

Plateau phase

Answer

Rapid repolarization

Answer

Final repolarization

Answer

Rapid depolarization

Question 2

Which of the following statements about the oculocardiac reflex is false?

Accepted Answer

It is mediated by oculomotor and vagus nerve

Answer

It is mediated by trigeminal and vagus nerve.

Answer

Reflex is more sensitive in neonates

Answer

It is characterized by bradycardia following traction on extra- ocular muscles

Question 3

What is the PRIMARY mechanism by which the Na+-Ca2+ exchanger functions in cardiac muscle cells?

Accepted Answer

Na+-Ca2+ exchanger acts to remove Ca2+ from heart muscle cells

Answer

Na+-Ca2+ exchanger requires ATP directly

Answer

The Na+-Ca2+ exchanger operates in reverse mode during normal cardiac contraction

Answer

The Na+-Ca2+ exchanger primarily moves Ca2+ into cardiac muscle cells during systole

Question 4

Cerebral blood flow is most directly increased by?

Accepted Answer

Increase in PCO2

Answer

Increase in PO2

Answer

Decrease metabolic rate

Answer

Increase in metabolic rate

Question 5

Which of the following statements is true about coronary circulation?

Accepted Answer

Major flow during diastole

Answer

Uniform flow during full cardiac cycle

Answer

Flow rate is approximately 500 ml/min

Answer

All of the above

Question 6

Where are the stretch receptors located in the left atrium?

Accepted Answer

Entrance of the pulmonary veins

Answer

None of the options

Answer

Atrioventricular septum

Answer

Septum between the atria

Question 7

What is the mechanism by which M2 receptors mediate the inhibition of the heart by the vagus nerve?

Accepted Answer

Inhibition of adenylate cyclase

Answer

Activation of phospholipase C

Answer

Inhibition of cAMP breakdown

Answer

Opening of voltage-gated calcium channels

Question 8

How many phases are there in the action potential of cardiac muscles?

Accepted Answer

5 phases

Answer

2 phases

Answer

3 phases

Answer

4 phases

Question 9

Coronary steal phenomenon caused due to

Accepted Answer

Preferential vasodilation of normal coronary vessels over stenotic vessels

Answer

Dilation of large coronary arteries

Answer

Dilation of epicardial coronary vessels

Answer

Dilation of capacitance vessels

Question 10

Which of the following is the most immediate cardiovascular response to acute stress?

Accepted Answer

Increased heart rate

Answer

Decreased heart rate

Answer

Release of cortisol

Answer

Decreased blood pressure

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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