Cardiovascular System Practice Questions

Q: Which of the following does NOT significantly contribute to the regulation of cerebral blood flow?

Potassium ions. ***Potassium ions*** - While potassium channels play a role in vascular smooth muscle function, extracellular **potassium ion concentration** does not significantly regulate overall cerebral blood flow within physiological ranges. - Changes in systemic potassium levels typically have more pronounced effects on cardiac and neuromuscular function compared to direct, significant regulation of cerebral vasculature. *Arterial PCO2* - **Arterial PCO2** is a potent regulator of cerebral blood flow; an increase in PCO2 leads to **vasodilation** and increased cerebral blood flow, while a decrease causes vasoconstriction. - This effect is mediated by changes in brain extracellular pH, which influences the tone of cerebral arterioles. *Blood pressure* - **Cerebral autoregulation** maintains stable cerebral blood flow despite changes in mean arterial blood pressure between approximately 60 and 150 mmHg. - Outside this range, very high or low **blood pressure** directly influences cerebral perfusion, making it a critical factor in cerebral blood flow regulation. *None of the options* - This option is incorrect because **potassium ions** do qualify as a factor that does NOT significantly contribute to cerebral blood flow regulation, making it the correct answer to this question.

Q: What is the effect of the Bainbridge reflex?

Increased heart rate. ***Increased heart rate*** - The **Bainbridge reflex** produces an increase in heart rate (tachycardia). - This reflex is triggered by an increase in **venous return** and **atrial distension**, which stimulates stretch receptors in the atria, leading to increased heart rate. - The reflex helps prevent venous pooling and maintains efficient cardiac function. *Bradycardia* - **Bradycardia** (slow heart rate) is the opposite effect of the Bainbridge reflex. - Other reflexes like the **baroreceptor reflex** can cause bradycardia when arterial pressure increases. *Increased cardiac output* - While increased heart rate can contribute to **increased cardiac output**, this is a secondary consequence, not the primary effect of the reflex. - Cardiac output = Heart rate × Stroke volume, so the direct effect is on heart rate. *Decreased venous return* - The Bainbridge reflex does not cause decreased venous return. - Instead, the reflex is **triggered by increased** venous return and responds by increasing heart rate to accommodate the increased blood flow.

Q: In hypovolemic shock there is -

Decreased cardiac output. ***Decreased cardiac output*** - **Hypovolemic shock** is fundamentally defined by **decreased circulating blood volume**, which leads to **decreased venous return** to the heart. - According to the **Frank-Starling mechanism**, decreased venous return leads to **decreased preload**, which results in **decreased stroke volume** and consequently **decreased cardiac output**. - This is the **primary hemodynamic characteristic** of hypovolemic shock and is present in ALL cases. - Decreased cardiac output triggers all the compensatory mechanisms seen in hypovolemic shock, including sympathetic activation and RAAS activation. *Afferent arteriolar constriction* - While afferent arteriolar constriction does occur in hypovolemic shock due to **sympathetic activation**, it is a **compensatory response** rather than the primary feature. - The predominant effect at the kidney level is actually a combination of both afferent and efferent arteriolar changes. - This occurs secondary to the decreased cardiac output. *Efferent arteriolar constriction* - **Efferent arteriolar constriction** is mediated primarily by **angiotensin II** and is actually MORE prominent than afferent constriction. - This helps **maintain glomerular filtration rate (GFR)** despite reduced renal blood flow by increasing glomerular hydrostatic pressure. - However, this is also a compensatory response, not the primary feature of hypovolemic shock. *Increased blood flow to kidney* - This is incorrect as hypovolemic shock causes **decreased renal blood flow**. - Blood is redistributed away from the kidneys to vital organs like the heart and brain through compensatory vasoconstriction.

Q: In the context of the jugular venous pulse, the C wave is seen during which phase of the cardiac cycle?

Isovolumetric contraction. ***Isovolumetric contraction*** - The **C wave** of the jugular venous pulse is caused by the bulging of the **tricuspid valve** into the right atrium during the **isovolumetric contraction** phase of the right ventricle. - This phase occurs just after the onset of ventricular contraction but before the pulmonary valve opens. *Slow filling at end of diastole* - This is not associated with the C wave. The slow filling phase of diastole (diastasis) occurs much earlier in the cardiac cycle. - The C wave occurs during early ventricular systole, specifically during isovolumetric contraction. *End of systole* - This period is typically associated with the **y descent**, as the tricuspid valve opens and atrial emptying occurs rapidly into the ventricle. - The C wave occurs at the beginning of systole, not at the end. *Start of diastole* - The start of diastole is characterized by the **opening of the tricuspid valve** and rapid ventricular filling, leading to the **y descent**. - The **C wave** specifically occurs during ventricular contraction (systole), not during the start of diastolic relaxation and filling.

Q: Endothelin primarily acts through which type of receptors?

Endothelin receptor type A (ETA). ***Endothelin receptor type A (ETA)*** - **ETA receptors** are primarily responsible for the **vasoconstrictive effects** of endothelin-1 in various tissues, leading to increased vascular tone and blood pressure. - Activation of **ETA receptors** on vascular smooth muscle cells mediates signaling pathways that result in **smooth muscle contraction**. *Endothelin receptor type B (ETB)* - **ETB receptors** have dual roles, mediating both **vasoconstriction** (via smooth muscle ETB) and **vasodilation** (via endothelial ETB, stimulating nitric oxide and prostacyclin release). - They also play a significant role in **clearance of endothelin-1** from circulation. *General receptor type (GPCRs)* - While **endothelin receptors (ETA and ETB)** are indeed **G protein-coupled receptors (GPCRs)**, "General receptor type (GPCRs)" is too broad and not the most specific answer for how endothelin *primarily acts*. - Endothelin's specific effects are mediated through its dedicated subtypes of GPCRs, not the general class. *Calcium receptors* - **Calcium receptors** (e.g., calcium-sensing receptors) are involved in sensing extracellular calcium levels and regulating calcium homeostasis. - Endothelin's mechanism involves **intracellular calcium mobilization** *after* receptor activation, but it does not act *through* calcium receptors.

Q: What is the primary change in fetal circulation that occurs at birth?

Closure of the foramen ovale. ***Closure of the foramen ovale*** - The **foramen ovale** undergoes functional closure within minutes of birth, making it the **primary immediate circulatory change** - At birth, the first breath causes **dramatic decrease in pulmonary vascular resistance** and **increased pulmonary blood flow**, which raises **left atrial pressure** - Simultaneously, umbilical cord clamping **increases systemic vascular resistance** and **decreases right atrial pressure** (loss of placental return) - This **pressure gradient reversal** (left atrial pressure > right atrial pressure) causes the **septum primum** to be pushed against the **septum secundum**, achieving functional closure - This immediately separates the systemic and pulmonary circulations, which is the **most critical primary change** in transitioning from fetal to neonatal circulation *Closure of the patent ductus arteriosus* - The **ductus arteriosus** undergoes **functional closure over 10-15 hours** after birth, followed by **anatomical closure over 2-3 weeks** - Closure occurs due to increased arterial oxygen tension and decreased prostaglandin E2 levels, causing smooth muscle constriction - While important, this is a **secondary change** that occurs more gradually compared to the immediate foramen ovale closure *Closure of the ductus venosus* - The **ductus venosus** closes functionally within 3-7 days as umbilical venous flow ceases - This redirects portal blood through the liver but does not directly impact the critical pulmonary-systemic circulation separation *Increased activity of the right ventricle* - After birth, the **left ventricle** becomes dominant as it pumps against higher systemic vascular resistance - The right ventricle actually experiences **decreased afterload** due to falling pulmonary vascular resistance - This is a consequence of, not the primary change in, the circulatory transition

Q: What is the most common mechanism responsible for causing arrhythmias in the heart?

Re-entry. ***Re-entry*** - **Re-entry** is the most common mechanism for arrhythmias and involves a re-excitation of cardiac tissue due to a circulating electrical impulse. - This requires at least two pathways with differing conduction velocities and refractory periods, creating a path for the impulse to re-excite an area after its normal refractory period has ended. *Early after depolarization* - **Early afterdepolarizations (EADs)** occur during phase 2 or 3 of the action potential when repolarization is incomplete, often due to prolonged action potential duration. - They are typically associated with conditions like **long QT syndrome** and can trigger polymorphic ventricular tachycardia, but are less common than re-entry. *Late after depolarization* - **Late afterdepolarizations (DADs)** occur during phase 4 of the action potential, after repolarization is complete, due to excessive intracellular calcium. - They are often seen in conditions like **digoxin toxicity** or **catecholaminergic polymorphic ventricular tachycardia**, but are not the most prevalent mechanism. *Automaticity* - **Abnormal automaticity** refers to pacemaker activity arising in non-pacemaker cells or an acceleration of normal pacemaker activity. - While it can cause arrhythmias such as accelerated idioventricular rhythm, re-entry is far more frequently implicated in the etiology of clinical arrhythmias.

Q: Inhibition of heart by vagus is mediated by which receptors?

M2. ***M2*** - The **vagus nerve** primarily mediates its inhibitory effects on the heart through **muscarinic M2 receptors**. - Activation of M2 receptors by **acetylcholine** (released from the vagus nerve) decreases heart rate and contractility. *M1* - **M1 receptors** are primarily found in neuronal tissue and glands, playing a role in **gastric acid secretion** and cognitive functions. - They are not the primary muscarinic subclass responsible for vagal inhibition of the heart. *NN* - **NN receptors** are **nicotinic receptors** found on postganglionic neurons in autonomic ganglia. - They are involved in **ganglionic transmission** and are not directly responsible for efferent vagal effects on the heart. *NM* - **NM receptors** are **nicotinic receptors** found at the **neuromuscular junction** of skeletal muscles. - Their activation leads to **skeletal muscle contraction**, and they have no role in regulating heart function.

Q: Inotropic effect of thyroid hormone is by ?

Enhancement of Catecholamines. ***Enhancement of Catecholamines*** - Thyroid hormones **potentiate the effects of catecholamines** (like adrenaline and noradrenaline) on the heart, leading to increased heart rate and contractility, which is an **inotropic effect**. - This occurs by increasing the number and sensitivity of **beta-adrenergic receptors** on cardiac muscle cells. *Membrane receptors* - While thyroid hormones do have some rapid, non-genomic effects that may involve **membrane receptors**, their primary and well-established inotropic effect is mediated indirectly through catecholamine sensitivity. - The classic action of thyroid hormones is via intracellular receptors that modulate gene expression, not direct membrane receptor signaling for inotropic effects. *cAMP* - **cAMP** is a common second messenger for many hormones, particularly those acting via G protein-coupled receptors. - While catecholamines themselves act through cAMP to exert their cardiac effects, thyroid hormones *enhance the action* of catecholamines rather than directly using cAMP as their primary inotropic mechanism. *cGMP* - **cGMP** is a second messenger often associated with nitric oxide signaling and vasodilation, contributing to cGMP-dependent protein kinases. - It is not the primary mediator for the *positive inotropic effect* of thyroid hormones on the heart.

Q: 'Flare' in Triple response is mediated by :

Axon reflex. ***Axon reflex*** - The "flare" component of the triple response is caused by an **axon reflex**, where sensory nerve endings release **vasoactive neuropeptides** such as substance P and calcitonin gene-related peptide (CGRP). - These neuropeptides cause **vasodilation** in the surrounding area, leading to the characteristic red, irregularly shaped halo around the wheal. *Arteriolar dilation* - While arteriolar dilation is a component of the triple response and contributes to the **redness (flush)** and **flare**, it is not the direct mediator of the flare itself. - The initial arteriolar dilation is primarily due to **histamine** acting directly on the vessels, whereas the flare is a broader, neurally mediated spread of vasodilation. *Histamine release* - **Histamine** release from mast cells is the primary mediator of the initial **redness (flush)** and the formation of the **wheal** (swelling due to capillary permeability). - While histamine plays a role in the overall response, it does not directly mediate the "flare" component, which involves neuronal signaling via the axon reflex. *Local hormones* - While various **local mediators** (which could be broadly considered "local hormones" in a sense) are involved in inflammatory responses, the specific term "local hormones" is too general and does not precisely describe the mechanism of the flare. - The axon reflex, involving specific **neuropeptides**, is the precise mechanism for the flare, not a general category of local hormones.

Question 1

Which of the following does NOT significantly contribute to the regulation of cerebral blood flow?

Accepted Answer

Potassium ions

Answer

Arterial PCO2

Answer

Blood pressure

Answer

None of the options

Question 2

What is the effect of the Bainbridge reflex?

Accepted Answer

Increased heart rate

Answer

Bradycardia

Answer

Increased cardiac output

Answer

Decreased venous return

Question 3

In hypovolemic shock there is -

Accepted Answer

Decreased cardiac output

Answer

Efferent arteriolar constriction

Answer

Increased blood flow to kidney

Answer

Afferent arteriolar constriction

Question 4

In the context of the jugular venous pulse, the C wave is seen during which phase of the cardiac cycle?

Accepted Answer

Isovolumetric contraction

Answer

Slow filling at end of diastole

Answer

End of systole

Answer

Start of diastole

Question 5

Endothelin primarily acts through which type of receptors?

Accepted Answer

Endothelin receptor type A (ETA)

Answer

Calcium receptors

Answer

General receptor type (GPCRs)

Answer

Endothelin receptor type B (ETB)

Question 6

What is the primary change in fetal circulation that occurs at birth?

Accepted Answer

Closure of the foramen ovale

Answer

Closure of the ductus venosus

Answer

Increased activity of the right ventricle

Answer

Closure of the patent ductus arteriosus

Question 7

What is the most common mechanism responsible for causing arrhythmias in the heart?

Accepted Answer

Re-entry

Answer

Early after depolarization

Answer

Late after depolarization

Answer

Automaticity

Question 8

Inhibition of heart by vagus is mediated by which receptors?

Accepted Answer

M2

Answer

M1

Answer

NN

Answer

NM

Question 9

Inotropic effect of thyroid hormone is by ?

Accepted Answer

Enhancement of Catecholamines

Answer

Membrane receptors

Answer

cAMP

Answer

cGMP

Question 10

'Flare' in Triple response is mediated by :

Accepted Answer

Axon reflex

Answer

Arteriolar dilation

Answer

Histamine release

Answer

Local hormones

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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