Cardiovascular System Practice Questions

Q: What is the normal range of interstitial pressure?

-5 to 0 mmHg. ***-5 to 0 mmHg*** - The interstitial fluid is normally under a **slight negative pressure**, typically ranging from **-5 to 0 mmHg** - This negative pressure helps pull fluid from the capillaries into the interstitial space and facilitates **lymphatic drainage** - Maintained by continuous drainage of fluid and proteins by the **lymphatic system** - This range is the commonly accepted value in standard physiology references for Indian medical exams *-3 to 0 mmHg* - While this range acknowledges the typically **negative nature** of interstitial pressure, it represents a slightly narrower range - Some sources cite this as the average range, but **-5 to 0 mmHg** is the more commonly accepted standard range - Not the most precise or widely cited range for exam purposes *0 to 5 mmHg* - This range suggests a **positive interstitial pressure**, which is generally **abnormal** - Indicates **edema formation** due to excess fluid accumulation in the interstitial space - Positive pressure impairs fluid reabsorption and lymphatic drainage - Represents pathological fluid dynamics *5 to 10 mmHg* - Represents significant **positive interstitial pressure** leading to severe **interstitial edema** - Markedly impairs tissue function and fluid exchange - Indicates pathological conditions where capillary filtration far exceeds lymphatic drainage capacity - Associated with severe edematous states

Q: Volume receptors are primarily located in which of the following?

Right and left atria. **Correct: *Right and left atria*** - The **atria** contain **low-pressure baroreceptors** (volume receptors) that primarily sense changes in circulating blood volume. - These receptors respond to stretching of the atrial walls, which occurs with increased blood volume, signaling the need for fluid excretion. *Incorrect: Carotid sinus and aortic arch* - These locations house **high-pressure baroreceptors** that primarily regulate **arterial blood pressure**, not circulating volume. - They respond to changes in the stretch of the arterial walls caused by blood pressure fluctuations. *Incorrect: Renal juxtaglomerular apparatus* - This apparatus primarily senses changes in **renal perfusion pressure** and **sodium delivery** to the distal tubule. - It plays a crucial role in regulating blood pressure and fluid balance through the **renin-angiotensin-aldosterone system (RAAS)**, but its primary role is not as a volume receptor. *Incorrect: Pulmonary arteries only* - While pulmonary baroreceptors exist, they primarily monitor **pulmonary arterial pressure** and do not serve as the main volume receptors for the systemic circulation. - Volume receptors are distributed more broadly within the low-pressure venous system.

Q: Which of the following ECG changes is not associated with hypokalemia?

Tall T wave. ***Tall T wave*** - **Tall, peaked T waves** are characteristic of **hyperkalemia**, reflecting rapid repolarization. - In **hypokalemia**, T waves are typically **flattened** or **inverted**, not tall. *Prolonged QRS interval* - A **prolonged QRS interval** can occur in severe hypokalemia due to slowed ventricular conduction. - This change indicates more severe electrolyte imbalance impacting the **depolarization phase** of ventricular myocytes. *Depressed ST segment* - **ST segment depression** is a common finding in hypokalemia, often associated with a reduced resting membrane potential. - This can indicate **myocardial ischemia** or simply the electrical instability caused by low potassium levels. *Prominent U waves* - **Prominent U waves** are a hallmark ECG finding in hypokalemia, often appearing as a deflection immediately following the T wave. - They are thought to represent delayed repolarization of **Purkinje fibers** or specific ventricular muscle cells.

Q: All of the following about the Bezold-Jarisch reflex are true except

Hypertension. ***Hypertension*** - The Bezold-Jarisch reflex is characterized by a **triad of responses**: **hypotension**, bradycardia, and apnea or respiratory depression. - **Hypertension** is therefore a finding that would **not be consistent** with the activation of this reflex. - The reflex causes **hypotension** through vasodilation and decreased cardiac output mediated by vagal activation. *Bradycardia* - **Bradycardia** is a classic component of the Bezold-Jarisch reflex, resulting from increased **vagal efferent activity** to the heart. - This response helps to reduce cardiac output and myocardial oxygen demand in the face of perceived noxious stimuli, such as myocardial ischemia. *Capsaicin* - **Capsaicin**, the active component of chili peppers, is known to **activate C-fiber afferents** in the heart and lungs, which are involved in triggering the Bezold-Jarisch reflex. - Experimental administration of capsaicin can reliably induce the components of this reflex through these sensory nerve activations. *Apnea* - The Bezold-Jarisch reflex can induce changes in respiration, typically presenting as **apnea** or **respiratory depression**. - This respiratory inhibition is thought to be mediated by activation of vagal afferents from the cardiopulmonary region. - The reflex causes respiratory **inhibition**, not stimulation.

Q: In which lead is the normal P wave inverted?

aVR. **Correct: *aVR*** - In lead **aVR**, the electrical activity is recorded from the perspective of the **right arm** towards the left foot and arm. Since the P wave represents atrial depolarization, which normally originates in the **sinoatrial node** in the right atrium and spreads leftward and inferiorly, the impulse moves away from the positive electrode of aVR. - This movement away from aVR's positive electrode causes a **negative (inverted)** deflection, which is a normal finding for the P wave in this lead. *Incorrect: LI* - Lead I records electrical activity between the **right arm (negative)** and the **left arm (positive)**. - As atrial depolarization moves towards the left arm, the P wave is normally **upright** in lead I. *Incorrect: LII* - Lead II records electrical activity between the **right arm (negative)** and the **left leg (positive)**. - Because atrial depolarization (from SA node) spreads downwards and to the left, it moves predominantly towards the positive electrode of lead II, resulting in an **upright** P wave. *Incorrect: aVF* - Lead aVF records electrical activity towards the **left foot (positive)**, providing an inferior view of the heart. - Since atrial depolarization moves inferiorly towards the left leg, the P wave in aVF is typically **upright**.

Q: During the cardiac cycle, the opening of the aortic valve takes place at the:

End of isovolumetric contraction. ***End of isovolumetric contraction*** - The **aortic valve opens** when the pressure in the left ventricle exceeds the pressure in the aorta, marking the end of **isovolumetric contraction** and the beginning of ventricular ejection. - During **isovolumetric contraction**, the mitral and aortic valves are closed, and ventricular pressure rises rapidly without a change in volume. *Beginning of systole* - The **beginning of systole** is marked by the closure of the mitral valve, initiating **isovolumetric contraction**, not the opening of the aortic valve. - Aortic valve opening occurs later in systole, after ventricular pressure has built sufficiently. *End of diastole* - The **end of diastole** is when the ventricles are maximally filled with blood, just before contraction begins. - At this point, the mitral valve is typically still open, and the aortic valve is closed. *End of diastasis* - **Diastasis** is the period of slow passive filling of the ventricles during mid-diastole. - The **end of diastasis** is followed by atrial contraction, which occurs before systole and before the aortic valve opens.

Q: Which of the following normally has a slowly depolarizing "prepotential"?

Sinoatrial node. ***Sinoatrial node*** - The **sinoatrial (SA) node** is the **normal primary pacemaker** of the heart, with cells that exhibit characteristic **slow depolarization** during phase 4 of their action potential, known as the **prepotential** or pacemaker potential. - This prepotential is primarily due to the **funny current (If)**, T-type Ca²⁺ channels, and decreasing K⁺ efflux, which gradually brings the membrane potential to threshold. - The SA node has the **fastest intrinsic rate** (60-100 bpm), which is why it normally dominates cardiac rhythm. *Atrial muscle cells* - Atrial muscle cells are **contractile cells** and do not spontaneously depolarize; they require an external stimulus from the SA node or other pacemaker cells. - Their action potential phase 4 maintains a **stable resting membrane potential** of about -90 mV, without prepotential. *Bundle of His* - The Bundle of His does possess **latent pacemaker activity** with a slowly depolarizing prepotential, but with a much slower intrinsic rate (40-60 bpm) than the SA node. - Under **normal conditions**, the SA node fires first and suppresses the Bundle of His through **overdrive suppression**, so it does not normally initiate the heartbeat. - It only becomes the dominant pacemaker if both the SA and AV nodes fail. *Purkinje fibers* - **Purkinje fibers** also have intrinsic pacemaker activity with a slowly depolarizing prepotential, but with the slowest rate (20-40 bpm) among cardiac pacemaker tissues. - Like the Bundle of His, they are **subsidiary pacemakers** that are normally suppressed by faster upstream pacemakers through overdrive suppression. - They only initiate rhythm in pathological conditions when higher pacemakers fail.

Q: Which of the following is the main factor for the ductus arteriosus closure postnatally?

Increase in partial pressure of oxygen (PaO2). ***Increase in partial pressure of oxygen (PaO2)*** - The **increase in PaO2** after birth causes a profound relaxation of the **pulmonary arterioles** and constriction of the **ductus arteriosus**. - This is the most crucial physiological change, leading to the **functional closure** of the ductus within hours of birth. *Postnatal increase in systemic vascular resistance* - While systemic vascular resistance (SVR) does increase postnatally as the **placental circulation** ceases, it is not the primary direct cause of ductus arteriosus closure. - An increased SVR contributes to the **pressure gradient** changes in the heart, but the oxygen-mediated constriction is more direct and powerful for the ductus itself. *Elevated levels of circulating prostaglandins* - **Prostaglandins**, particularly PGE2, are responsible for **maintaining the patency** of the ductus arteriosus *in utero*. - After birth, the **decrease in prostaglandin levels** (due to lung metabolism and removal of the placenta) is essential for closure, but elevated levels would actually keep it open. *Reduction in pulmonary vascular resistance* - A reduction in **pulmonary vascular resistance (PVR)** is indeed a significant postnatal change, allowing for increased pulmonary blood flow. - While this change alters blood flow dynamics, the direct cause of ductus arteriosus constriction is the **increased PaO2**, not solely the fall in PVR.

Q: The largest component of the total peripheral resistance is due to:

Arterioles. ***Arterioles*** - **Arterioles** are the primary site of **resistance** in the cardiovascular system due to their relatively small diameter and the significant ability of their **smooth muscle** walls to constrict or dilate. - This resistance plays a crucial role in regulating **blood flow** to various organs and contributes to **mean arterial pressure**. *Venules* - **Venules** are primarily involved in collecting blood from capillaries and have relatively low resistance compared to arteries and arterioles. - While they contribute to capacitance, their impact on **total peripheral resistance** is minimal. *Capillaries* - Although **capillaries** have very small diameters, their sheer number in parallel reduces the overall resistance of the capillary bed. - The primary function of capillaries is **exchange** of nutrients and waste, not primarily resistance. *Precapillary sphincters* - **Precapillary sphincters** control blood flow *into* capillaries from arterioles, acting as gates. - While they regulate flow to specific capillary beds, they are not the largest *component* of total systemic resistance; the **arterioles themselves** are.

Q: The following data were obtained from a man weighing 70 kg: Aorta oxygen (O2) content is 20.0 vol%, femoral vein O2 content is 16 vol%, coronary sinus O2 content is 10 vol%, and pulmonary artery O2 content is 15 vol%. What is the cardiac output of this man, given a total body O2 consumption of 400 ml/min?

8 L/min. ***8 L/min*** - The cardiac output is calculated using the **Fick principle**: CO = Total body O2 consumption / (Arterial O2 content - Mixed venous O2 content). - In this case, **Arterial O2 content is 20 vol%** and **Mixed venous O2 content (pulmonary artery) is 15 vol%**. So, CO = 400 ml/min / (20 vol% - 15 vol%) = 400 ml/min / 5 ml O2/100 ml blood = 400 / 0.05 = 8000 ml/min = **8 L/min**. *10 L/min* - This result would be obtained if the arteriovenous oxygen difference was smaller, specifically 4 vol% (400 / 0.04 = 10000 ml/min). - This calculation does not correctly use the given **mixed venous O2 content** from the pulmonary artery. *6 L/min* - This result would be obtained if the arteriovenous oxygen difference was larger, specifically 6.67 vol% (400 / 0.0667 ≈ 6000 ml/min). - This calculation misrepresents the **actual O2 extraction** from the arterial blood. *5 L/min* - This result would be obtained if the arteriovenous oxygen difference was 8 vol% (400 / 0.08 = 5000 ml/min). - This choice indicates an incorrect application of the **Fick principle** or misidentification of the relevant oxygen content values.

Question 1

What is the normal range of interstitial pressure?

Accepted Answer

-5 to 0 mmHg

Answer

-3 to 0 mmHg

Answer

0 to 5 mmHg

Answer

5 to 10 mmHg

Question 2

Volume receptors are primarily located in which of the following?

Accepted Answer

Right and left atria

Answer

Carotid sinus and aortic arch

Answer

Pulmonary arteries only

Answer

Renal juxtaglomerular apparatus

Question 3

Which of the following ECG changes is not associated with hypokalemia?

Accepted Answer

Tall T wave

Answer

Prolonged QRS interval

Answer

Prominent U waves

Answer

Depressed ST segment

Question 4

All of the following about the Bezold-Jarisch reflex are true except

Accepted Answer

Hypertension

Answer

Bradycardia

Answer

Capsaicin

Answer

Apnea

Question 5

In which lead is the normal P wave inverted?

Accepted Answer

aVR

Answer

LI

Answer

LII

Answer

aVF

Question 6

During the cardiac cycle, the opening of the aortic valve takes place at the:

Accepted Answer

End of isovolumetric contraction

Answer

Beginning of systole

Answer

End of diastole

Answer

End of diastasis

Question 7

Which of the following normally has a slowly depolarizing "prepotential"?

Accepted Answer

Sinoatrial node

Answer

Atrial muscle cells

Answer

Bundle of His

Answer

Purkinje fibers

Question 8

Which of the following is the main factor for the ductus arteriosus closure postnatally?

Accepted Answer

Increase in partial pressure of oxygen (PaO2)

Answer

Elevated levels of circulating prostaglandins

Answer

Reduction in pulmonary vascular resistance

Answer

Postnatal increase in systemic vascular resistance

Question 9

The largest component of the total peripheral resistance is due to:

Accepted Answer

Arterioles

Answer

Venules

Answer

Capillaries

Answer

Precapillary sphincters

Question 10

The following data were obtained from a man weighing 70 kg: Aorta oxygen (O2) content is 20.0 vol%, femoral vein O2 content is 16 vol%, coronary sinus O2 content is 10 vol%, and pulmonary artery O2 content is 15 vol%. What is the cardiac output of this man, given a total body O2 consumption of 400 ml/min?

Accepted Answer

8 L/min

Answer

10 L/min

Answer

6 L/min

Answer

5 L/min

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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