Cardiovascular System Practice Questions

Q: Where is the highest oxygen concentration present in fetal circulation

IVC. ***Correct: IVC (Inferior Vena Cava)*** - The IVC has the **highest oxygen concentration (~67% saturation)** among the vessels listed in fetal circulation - It receives **oxygenated blood from the placenta** via the umbilical vein, which continues as the ductus venosus and drains into the IVC - This well-oxygenated blood is preferentially shunted through the **foramen ovale** to the left atrium, then to the left ventricle and ascending aorta to supply the brain and heart *Incorrect: SVC (Superior Vena Cava)* - Carries **deoxygenated blood** from the upper body with oxygen saturation of only ~40% - Returns systemic venous blood without placental oxygenation *Incorrect: Right Ventricle* - Contains **mixed blood** from both SVC (deoxygenated) and IVC (oxygenated) - Has intermediate oxygen saturation (~52%) lower than the IVC alone *Incorrect: Aorta* - The **descending aorta** receives poorly oxygenated blood (~58%) from the ductus arteriosus - Even the ascending aorta (~62%) has slightly lower saturation than the IVC - The question asks for the highest concentration, which is the IVC before mixing occurs

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: 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: 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 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: 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: In an ECG the cardiac event corresponding to the ST segment is:

Ventricular repolarisation. ***Ventricular repolarisation*** - The **ST segment** represents the **early phase of ventricular repolarization**, corresponding to the **plateau phase (Phase 2)** of the ventricular action potential. - During this phase, the ventricles are completely depolarized and calcium influx balances potassium efflux, creating an isoelectric (flat) segment on the ECG. - The ST segment extends from the **end of the QRS complex (J point)** to the **beginning of the T wave**, after which rapid repolarization occurs. - Together, the **ST segment and T wave** represent the complete process of ventricular repolarization. *Atrial depolarisation* - **Atrial depolarization** is represented by the **P wave** on the ECG, not the ST segment. - This occurs first in the cardiac cycle, triggering atrial contraction and filling of the ventricles. *Ventricular depolarisation* - **Ventricular depolarization** is represented by the **QRS complex**, which immediately **precedes** the ST segment. - This event triggers ventricular contraction (systole) and occurs before the plateau phase. *Atrial repolarisation* - **Atrial repolarization** occurs during the QRS complex and is **obscured** by the much larger electrical signal from ventricular depolarization. - It is not visible as a separate deflection on the standard ECG.

Q: Cerebral blood flow is regulated by all, EXCEPT:

Potassium ions. ***Potassium ions*** - While potassium ions play a crucial role in neuronal excitability and membrane potential, they are **not a primary direct regulator** of cerebral blood flow (CBF) in the same way as other factors listed. - Changes in extracellular potassium can affect vascular smooth muscle, but their direct impact on CBF auto-regulation is less pronounced compared to metabolic or pressure-related factors. *Intracranial pressure* - **Increased intracranial pressure (ICP)** can significantly decrease cerebral blood flow due to the **Monro-Kellie doctrine**, which states that an increase in ICP reduces the cerebral perfusion pressure (CPP). - A sustained and significant elevation in ICP can lead to **cerebral ischemia** as it opposes the arterial pressure driving blood into the brain. *Arterial PCO2* - **Arterial PCO2** is a potent regulator of cerebral blood flow, with **hypercapnia (high PCO2)** causing **vasodilation** and increased CBF. - Conversely, **hypocapnia (low PCO2)** leads to **vasoconstriction** and decreased CBF, which is a key mechanism in the management of cerebral edema. *Cerebral metabolic rate* - **Cerebral metabolic rate (CMR)** is directly coupled to cerebral blood flow, meaning that regions of the brain with higher metabolic activity receive increased blood flow. - This **neurovascular coupling** ensures adequate supply of oxygen and nutrients to meet the brain's metabolic demands.

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

Where is the highest oxygen concentration present in fetal circulation

Accepted Answer

IVC

Answer

SVC

Answer

Right ventricle

Answer

Aorta

Question 2

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 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

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 5

What is the effect of the Bainbridge reflex?

Accepted Answer

Increased heart rate

Answer

Bradycardia

Answer

Increased cardiac output

Answer

Decreased venous return

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

In an ECG the cardiac event corresponding to the ST segment is:

Accepted Answer

Ventricular repolarisation

Answer

Atrial depolarisation

Answer

Ventricular depolarisation

Answer

Atrial repolarisation

Question 9

Cerebral blood flow is regulated by all, EXCEPT:

Accepted Answer

Potassium ions

Answer

Intracranial pressure

Answer

Cerebral metabolic rate

Answer

Arterial PCO2

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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