Cardiovascular System Practice Questions

Q: Aortic valve closure occurs in which part of cardiac cycle?

Beginning of isovolumetric relaxation. ***Beginning of isovolumetric relaxation*** - Aortic valve closure marks the end of **ventricular systole** and the start of **isovolumetric relaxation**, as blood ceases to be ejected and the ventricle begins to relax while remaining closed. - This event corresponds to the **second heart sound (S2)** and signifies the beginning of a period where ventricular volume remains constant, but pressure drops. *Beginning of isovolumetric contraction* - This phase begins with the closure of the **mitral and tricuspid valves** (first heart sound, S1), as ventricular pressure rises but volume remains constant before ejection. - The aortic valve is still closed at this point, as ventricular pressure is not yet high enough to open it. *Beginning of ventricular ejection* - This phase begins when the **aortic valve opens** as ventricular pressure exceeds aortic pressure, allowing blood to be ejected from the left ventricle. - Aortic valve closure occurs *after* ejection, not at its beginning. *During rapid ventricular filling* - Rapid ventricular filling occurs when the **mitral valve opens** (following isovolumetric relaxation), allowing blood to flow from the atria into the ventricles. - During this phase, the aortic valve is closed, but its closure happened earlier, at the beginning of isovolumetric relaxation.

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: 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: 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: 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: 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: Aortic valve closure corresponds to the beginning of which phase of the cardiac cycle?

Isovolumetric relaxation. ***Isovolumetric relaxation*** - **Aortic valve closure** marks the end of **ventricular ejection** and the beginning of **isovolumetric relaxation** as both the aortic and mitral valves are closed, and ventricular pressure drops without a change in volume. - This phase is vital for the heart to relax and prepare for filling, corresponding to the **second heart sound (S2)**. *Systole* - **Systole** refers to the **contraction phase** of the heart, encompassing both isovolumetric contraction and ventricular ejection. - Aortic valve closure signifies the end of the **ejection phase** of systole, not its beginning. *Parasystole* - **Parasystole** is an **arrhythmia** where an ectopic pacemaker competes with the normal sinus rhythm, leading to independent atrial or ventricular contractions. - It is a **pathological condition** and not a normal phase of the cardiac cycle. *Isovolumetric contraction* - **Isovolumetric contraction** occurs after the **mitral valve closes** and before the aortic valve opens, causing pressure to build in the ventricle. - This phase precedes **ventricular ejection** and is initiated by mitral valve closure, not aortic valve closure.

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.

Question 1

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 2

Aortic valve closure occurs in which part of cardiac cycle?

Accepted Answer

Beginning of isovolumetric relaxation

Answer

Beginning of isovolumetric contraction

Answer

During rapid ventricular filling

Answer

Beginning of ventricular ejection

Question 3

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 4

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 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

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 7

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 8

Aortic valve closure corresponds to the beginning of which phase of the cardiac cycle?

Accepted Answer

Isovolumetric relaxation

Answer

Systole

Answer

Parasystole

Answer

Isovolumetric contraction

Question 9

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 10

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

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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