Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 871: In a healthy person, arterial baroreceptor activity is seen at what stage of the cardiac cycle?

A. None of the options
B. Diastole
C. Systole
D. Both (Correct Answer)

Explanation: ***Both*** - Baroreceptors respond to changes in **arterial pressure**, which fluctuates throughout both systole and diastole. - The baroreflex mechanism is continuously active, monitoring and adjusting blood pressure through changes in **heart rate**, **contractility**, and **vascular resistance** during both phases of the cardiac cycle. *Systole* - While baroreceptors are active during systole due to the **rise in arterial pressure**, they are not exclusively active during this phase. - Their primary role is to detect and respond to the **peak pressure** changes that occur during **ejection**, but their activity extends beyond this. *Diastole* - Baroreceptors continue to fire during diastole, albeit at a lower rate, as blood pressure falls; however, their activity is not limited to this phase alone. - They monitor the **decline in pressure** to help regulate the overall mean arterial pressure, not just the trough. *None of the options* - This option is incorrect because arterial baroreceptors are indeed active and crucial for blood pressure regulation throughout the entire cardiac cycle, encompassing both systole and diastole. - Their continuous monitoring is essential for maintaining **hemodynamic stability**.

Question 872: All are true about baroreceptors, except?

A. Stimulated when BP decreases (Correct Answer)
B. Stimulation causes increased vagal discharge
C. Stimulate nucleus ambiguus
D. Afferents are through sino-aortic nerves

Explanation: ***Stimulated when BP decreases*** - Baroreceptors are **stretch receptors** located in the walls of the carotid sinus and aortic arch. - They are stimulated by an **increase in blood pressure (BP)**, which causes stretching of the arterial walls, not by a decrease. *Afferents are through sino-aortic nerves* - This statement is **true**. Afferent impulses from the carotid sinus baroreceptors travel via the **glossopharyngeal nerve (IX)**, and those from the aortic arch baroreceptors travel via the **vagus nerve (X)**. - These nerves collectively form the **sino-aortic nerves** that relay information to the brainstem. *Stimulation causes increased vagal discharge* - This statement is **true**. When baroreceptors are stimulated by **increased BP**, they send signals to the cardiovascular center in the medulla. - This leads to increased **parasympathetic (vagal) outflow** to the heart, causing a decrease in heart rate and contractility, and inhibition of sympathetic outflow. *Stimulate nucleus ambiguus* - This statement is **true**. The **nucleus ambiguus** is a brainstem nucleus that contains the cell bodies of preganglionic parasympathetic neurons that contribute to the vagus nerve. - Baroreceptor stimulation leads to activation of the nucleus ambiguus, thereby increasing **vagal output** to the heart.

Question 873: What is the blood supply of the liver in ml/min/100g?

A. 1500-2000 ml/min/100g
B. 1000-1500 ml/min/100g
C. 50-60 ml/min/100g (Correct Answer)
D. 250-300 ml/min/100g

Explanation: ***50-60 ml/min/100g*** - The liver receives a substantial blood supply, but when expressed per 100 grams of tissue, the value is around **50-60 mL/min/100g**. This demonstrates the organ's high metabolic demand. - This value represents the total blood flow from both the **hepatic artery** and the **portal vein** per unit weight of liver tissue. *1500-2000 ml/min/100g* - This value is extremely high and does not accurately represent the **blood flow per 100g of liver tissue**. Such a high flow rate would imply an unrealistic perfusion. - While the total blood flow to the liver is large, it's not at this magnitude when normalized to tissue weight. *1000-1500 ml/min/100g* - This range is closer to the **total blood flow to the entire liver** (1000-1800 ml/min), not the blood flow per 100 grams of tissue. - It's crucial to differentiate between total organ flow and flow density (per 100g). *250-300 ml/min/100g* - This value is significantly higher than the actual blood supply per 100g of liver tissue, suggesting an overestimation of the **perfusion density**. - While the liver is highly perfused, this rate is not physiologically accurate when normalized to the tissue weight.

Question 874: What physiological mechanism leads to an increase in cardiac output?

A. Inhalation
B. Increased myocardial contractility (Correct Answer)
C. Increased parasympathetic activity
D. Transitioning from a supine to a standing position

Explanation: ***Increased myocardial contractility*** - **Increased myocardial contractility** directly leads to a greater **stroke volume** (the amount of blood pumped with each beat), thus increasing cardiac output (Cardiac Output = Stroke Volume × Heart Rate). - This can be stimulated by factors such as **sympathetic nervous system activation** or positive inotropic agents. *Inhalation* - While inhalation can temporarily affect venous return and intrathoracic pressure, it does not directly or consistently lead to a sustained increase in **cardiac output**. - Its primary effect is on **respiration**, not cardiac performance. *Increased parasympathetic activity* - Increased parasympathetic activity, primarily via the **vagus nerve**, acts to **decrease heart rate** and myocardial contractility. - This effect would typically **reduce cardiac output**, not increase it. *Transitioning from a supine to a standing position* - Transitioning to a standing position usually causes a **temporary decrease in venous return** and a brief drop in cardiac output as blood pools in the lower extremities. - The body then compensates by increasing heart rate and peripheral vascular resistance to maintain blood pressure, but the initial effect on cardiac output is generally a transient decrease.

Question 875: In pregnancy, plasma volume increase is maximum at what gestational age?

A. 10 wks
B. 20 wks
C. 25 wks
D. 30 wks (Correct Answer)

Explanation: ***30 wks*** - **Plasma volume** typically reaches its maximum expansion around **30-34 weeks of gestation**, increasing by approximately 40-50% compared to pre-pregnancy levels. - This increase is crucial for supporting the **fetoplacental unit**, enhancing nutrient delivery, and protecting against supine hypotension. *10 wks* - At **10 weeks**, the increase in plasma volume is still modest, with significant expansion primarily occurring in the **second trimester**. - Most of the rapid expansion begins after the **first trimester**, around the 12-week mark. *20 wks* - While plasma volume is significantly increasing by **20 weeks**, it has not yet reached its peak. - The continuous expansion continues through the **third trimester** before stabilizing. *25 wks* - At **25 weeks**, plasma volume is substantially elevated, but the maximum expansion is usually observed a few weeks later. - The peak is generally in the **early third trimester**, around 30-34 weeks.

Question 876: Which of the following statements regarding fetal circulation is correct?

A. The presence of fetal hemoglobin shifts the oxyhemoglobin dissociation curve to the right.
B. The foramen ovale closes before birth.
C. PO2 of fetal blood leaving the placenta is higher than maternal mixed venous PO2.
D. The heart of the fetus receives blood with higher oxygen saturation than maternal mixed venous blood. (Correct Answer)

Explanation: ***The heart of the fetus receives blood with higher oxygen saturation than maternal mixed venous blood.*** - The **umbilical vein** carries oxygenated blood from the placenta with an oxygen saturation of approximately **80-85%**, which is higher than maternal mixed venous blood saturation of approximately **75%**. - Through preferential streaming via the **ductus venosus** and **foramen ovale**, a significant portion of this highly oxygenated blood reaches the **left atrium** and **left ventricle**, ensuring that the fetal heart muscle and brain receive blood with relatively high oxygen saturation. - The **coronary arteries** supplying the fetal heart arise from the ascending aorta, which receives this preferentially oxygenated blood, allowing the fetal myocardium to receive blood with higher oxygen saturation than maternal mixed venous blood. *PO2 of fetal blood leaving the placenta is higher than maternal mixed venous PO2.* - This statement is **INCORRECT**. The **PO2 of fetal blood** leaving the placenta (umbilical vein) is approximately **30-35 mmHg**, which is actually **lower** than maternal mixed venous PO2 of approximately **40 mmHg**. - However, despite the lower PO2, fetal blood has adequate oxygen content due to **fetal hemoglobin (HbF)** having higher oxygen affinity and the higher hemoglobin concentration in fetal blood. *The presence of fetal hemoglobin shifts the oxyhemoglobin dissociation curve to the right.* - This statement is **INCORRECT**. **Fetal hemoglobin (HbF)** has a higher affinity for oxygen than adult hemoglobin (HbA), binding oxygen more readily at lower partial pressures. - This results in a **leftward shift** of the oxyhemoglobin dissociation curve, not a rightward shift, facilitating oxygen uptake from maternal blood across the placenta. *The foramen ovale closes before birth.* - This statement is **INCORRECT**. The **foramen ovale** is an opening between the right and left atria that allows oxygenated blood to bypass the pulmonary circulation in utero. - It remains open throughout fetal life and typically closes **shortly after birth** (within hours to days) due to increased left atrial pressure from increased pulmonary blood flow and decreased right atrial pressure.

Question 877: Which of the following statements about cardiac muscle is true?

A. Cardiac muscle fibers are arranged in sheets.
B. Cardiac muscle cells have centrally located nuclei. (Correct Answer)
C. Cardiac muscle fibers are spindle-shaped.
D. Cardiac muscle lacks gap junctions.

Explanation: ***Cardiac muscle cells have centrally located nuclei.*** - Unlike **skeletal muscle** cells which have multiple, peripherally located nuclei, cardiac muscle cells typically have one or two **centrally located nuclei**. - This is a key distinguishing histological feature when observing cardiac muscle tissue under a microscope. *Cardiac muscle fibers are arranged in sheets.* - While cardiac muscle forms the walls of the heart, its individual fibers (cells) are **branched** and interconnected, not typically described as being arranged in discrete sheets. - The arrangement allows for a **syncytium-like functionality**, enabling coordinated contraction. *Cardiac muscle fibers are spindle-shaped.* - **Spindle-shaped cells** with a single central nucleus are characteristic of **smooth muscle**, not cardiac muscle. - Cardiac muscle cells are branched and generally cylindrical with blunt ends. *Cardiac muscle lacks gap junctions.* - Cardiac muscle cells are abundant in **gap junctions**, which are critical for electrical coupling and synchronous contraction. - These gap junctions are located within **intercalated discs** and allow for rapid propagation of action potentials between cells.

Question 878: What is the duration of the second heart sound (S2)?

A. 0.15 sec
B. 0.1 sec
C. 0.12 sec
D. 0.08 sec (Correct Answer)

Explanation: ***0.08 sec*** - The second heart sound (S2) is composed of two components: A2 (aortic valve closure) and P2 (pulmonic valve closure). The normal duration of S2, encompassing both components, is approximately **0.08 seconds**. - This short duration reflects the rapid closure of the aortic and pulmonic valves at the beginning of **diastole**. *0.15sec* - A duration of **0.15 seconds** for S2 is significantly longer than normal, which could indicate abnormal valve function or conditions causing delayed valve closure. - Such prolonged duration might be observed in conditions like **severe pulmonic stenosis** or **pulmonic hypertension**, which are not the typical duration of a healthy S2. *0.12 sec* - A duration of **0.12 seconds** is also longer than the typical normal range for S2. - While still shorter than 0.15 seconds, it could suggest subtle delays in valve closure or splitting that exceeds the usual physiological splitting. *0.1 sec* - A duration of **0.1 seconds** is slightly prolonged but generally falls within a range that might be considered borderline or indicative of minimal physiological variations. - However, in typical healthy individuals, the S2 duration is closer to 0.08 seconds, making 0.1 seconds less precise for the most common duration.

Question 879: What does Einthoven's law state regarding the relationship between the electrical potentials of the limb leads?

A. I + III = II (Correct Answer)
B. I - III = II
C. I + II + III = 0
D. I + III = avL

Explanation: ***I + III = II*** - Einthoven's law describes the relationship between the three **bipolar limb leads** (I, II, and III) in an **electrocardiogram (ECG)**. - It states that the electrical potential of Lead II is equal to the sum of the potentials of Lead I and Lead III (Lead II = Lead I + Lead III). - This can also be expressed as **I + III = II**, which is the **correct mathematical representation** of Einthoven's law. *I - III = II* - This equation is **incorrect** and does not represent Einthoven's law. - The correct relationship involves **addition** of Leads I and III, not subtraction. *I + II + III = 0* - This equation is **incorrect** as written with all positive signs. - Einthoven's law can be rearranged as **I + III - II = 0** (not I + II + III = 0). - The equation shown suggests adding all three leads to get zero, which is **mathematically inconsistent** with the correct formulation (I + III = II). *I + III = avL* - This equation is incorrect and does not relate to Einthoven's law. - **avL (augmented vector left)** is one of the augmented unipolar limb leads calculated as: avL = I - (II/2), not as a direct sum of Leads I and III.

Question 880: Mean arterial pressure is calculated as:

A. (DBP+3SBP)/2
B. (SBP+3DBP)/2
C. (DBP+2SBP)/3
D. (SBP+2DBP)/3 (Correct Answer)

Explanation: ***(SBP+2DBP)/3*** - This formula accurately calculates **mean arterial pressure (MAP)**, emphasizing the longer duration of diastole compared to systole in the cardiac cycle. - The diastolic blood pressure (**DBP**) is weighted twice as much as the systolic blood pressure (**SBP**) to reflect this physiological difference. *(DBP+2SBP)/3* - This formula incorrectly weighs the diastolic pressure less and the systolic pressure more, which does not reflect the **physiological duration of the cardiac cycle**. - While it attempts to average pressures, it does not correctly represent the **mean perfusion pressure**. *(SBP+3DBP)/2* - This formula is inaccurate for calculating MAP as the **denominator should be 3**, not 2, to account for the three components being averaged (one SBP and two DBP). - It also disproportionately weights **DBP** too high relative to the standard physiological formula. *(DBP+3SBP)/2* - This formula is incorrect as it applies an **excessive weighting to SBP** and uses an incorrect denominator. - It would yield a significantly higher and inaccurate value for **mean arterial pressure**.

Practice by Chapter

Cardiac Electrophysiology

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Cardiac Cycle

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Cardiac Output and Its Regulation

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Hemodynamics and Blood Flow

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Arterial System Physiology

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Microcirculation and Lymphatics

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Venous Return and Central Venous Pressure

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Cardiovascular Reflexes

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Regional Circulations

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Cardiovascular Responses to Exercise and Stress

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