Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 871: Which hormone is primarily responsible for regulating blood pressure in response to significant blood loss due to hemorrhage?

A. Vasopressin (ADH)
B. Aldosterone
C. Epinephrine (Adrenaline) (Correct Answer)
D. Atrial Natriuretic Peptide (ANP)

Explanation: ***Epinephrine (Adrenaline)*** - Released rapidly from the **adrenal medulla** within seconds of hemorrhage as part of the **sympathetic-adrenal response** - Acts as the **primary immediate hormonal response** to severe blood loss, triggering the acute stress response - **Increases heart rate and contractility** (β1 receptors), causes **vasoconstriction** in peripheral vessels (α1 receptors), and **bronchodilation** (β2 receptors) - These combined effects rapidly **maintain blood pressure** and ensure perfusion to vital organs (heart, brain) - Represents the classic **fight-or-flight hormonal response** to acute hemorrhagic stress *Vasopressin (ADH)* - Also plays a **significant role** in hemorrhagic response, with levels increasing dramatically (up to 50-100 fold) - At high concentrations during severe hemorrhage, ADH acts as a **potent vasoconstrictor** via V1 receptors on vascular smooth muscle - Additionally promotes **water reabsorption** in kidneys via V2 receptors to help restore blood volume - However, while vasopressin contributes importantly to blood pressure maintenance, **epinephrine represents the primary immediate hormonal response** in the acute phase - The combined sympathetic-adrenal (catecholamine) response is traditionally considered the first-line hormonal defense *Aldosterone* - A **mineralocorticoid** involved in **longer-term regulation** of blood pressure and volume - Promotes **sodium and water reabsorption** in the distal tubules and collecting ducts, along with **potassium excretion** - Its effects take **hours to days** to manifest, making it important for sustained volume restoration but not the primary acute response to hemorrhage - Part of the RAAS (Renin-Angiotensin-Aldosterone System) activated after hemorrhage *Atrial Natriuretic Peptide (ANP)* - Released from atrial myocytes in response to **atrial stretch** from high blood volume and pressure - Promotes **vasodilation**, **sodium and water excretion** (natriuresis and diuresis), and inhibits renin and aldosterone - Its actions are **counterproductive** during hemorrhage, as they would further lower blood pressure and volume - ANP levels typically **decrease** during hemorrhage, not increase

Question 872: 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 873: P wave is due to:

A. Atrial depolarization (Correct Answer)
B. Atrial repolarization
C. Ventricular depolarization
D. Ventricular repolarization

Explanation: **Atrial depolarization** - The **P wave** on an electrocardiogram (ECG) represents the electrical activity associated with the **depolarization of the atria**. - This depolarization leads to **atrial contraction**, pushing blood into the ventricles. *Atrial repolarization* - **Atrial repolarization** also occurs but is usually hidden within the **QRS complex** and thus not separately visible as a distinct wave on a standard ECG. - While it's an electrical event, it does not produce the P wave. *Ventricular depolarization* - **Ventricular depolarization** is represented by the **QRS complex** on an ECG. - This electrical activity leads to **ventricular contraction**, pumping blood out of the heart. *Ventricular repolarization* - **Ventricular repolarization** is represented by the **T wave** on an ECG. - This process allows the ventricles to relax and refill with blood.

Question 874: When blood pressure falls below 40 mm Hg, which mechanism of regulation is working?

A. CNS ischemic reflex (Correct Answer)
B. Chemoreceptor response
C. Baroreceptor response
D. None of the options

Explanation: ***CNS ischemic reflex*** - The **CNS ischemic reflex** is activated when blood pressure falls below 60 mmHg, with maximal activation below 40 mmHg, indicating severe ischemia in the brain's vasomotor center. - This reflex elicits an intense **sympathetic vasoconstriction** and cardiac stimulation to prioritize blood flow to the brain even at the expense of other organs. *Chemoreceptor response* - The chemoreceptor reflex is primarily activated by a decrease in **arterial pO2**, an increase in **pCO2**, or a decrease in **pH**. - While it can increase blood pressure, it is not the primary or most profound regulatory mechanism specifically triggered by extremely low blood pressure (below 40 mmHg) to prevent brain ischemia. *Baroreceptor response* - **Baroreceptors** are most sensitive to changes in blood pressure within the normal to moderately hypotensive range (e.g., 60-180 mmHg). - At very low pressures (below 40-50 mmHg), baroreceptors become **less sensitive** or "saturated," and their effectiveness in raising blood pressure significantly diminishes. *None of the options* - This option is incorrect because the **CNS ischemic reflex** specifically functions as a powerful, last-ditch mechanism to maintain cerebral blood flow during severe hypotension which is a life saving reflex during conditions like hemorrhage.

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 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 877: 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 878: Which of the following factors increases stroke volume?

A. Increased end-diastolic and end-systolic volumes
B. Decreased end-diastolic and end-systolic volumes
C. Increased end-diastolic volume and decreased end-systolic volume (Correct Answer)
D. Decreased end-diastolic volume and increased end-systolic volume

Explanation: ***Increased end-diastolic volume and decreased end-systolic volume*** - **Stroke volume (SV)** is calculated as **End-Diastolic Volume (EDV)** minus **End-Systolic Volume (ESV)**. Therefore, increasing the volume before contraction while decreasing the volume after contraction will maximize the ejected blood. - A higher **EDV** signifies greater **preload** (more blood filling the ventricle), and a lower **ESV** indicates more complete ejection of blood, often due to increased **contractility** or decreased **afterload**. *Increased end-diastolic and end-systolic volumes* - While an **increased EDV** would tend to increase stroke volume, an **increased ESV** suggests that the heart is ejecting less blood per beat, which would decrease stroke volume. - The combined effect makes it less likely to unequivocally increase stroke volume, as the increase in ESV might offset or even surpass the effect of increased EDV. *Decreased end-diastolic and end-systolic volumes* - Both a **decreased EDV** (less filling) and a **decreased ESV** (more complete ejection) work against each other in terms of stroke volume calculation. - If **EDV** decreases, there's less blood to eject, and if the decrease in **EDV** is proportionally larger than the decrease in **ESV**, stroke volume will decrease. *Decreased end-diastolic volume and increased end-systolic volume* - A **decreased EDV** means less blood is available for ejection, reducing preload and the amount of blood the heart can pump. - An **increased ESV** means the heart is ejecting less blood with each beat, indicating reduced contractility or increased afterload, both of which would decrease stroke volume.

Question 879: Which one of the following is the CORRECT statement regarding coronary blood flow?

A. Coronary blood flow is directly related to perfusion pressure and inversely related to resistance (Correct Answer)
B. Coronary blood flow is inversely related to perfusion pressure and directly related to resistance
C. Coronary blood flow is directly related to perfusion pressure and also to resistance
D. Coronary blood flow is inversely related to both pressure and resistance

Explanation: ***Coronary blood flow is directly related to perfusion pressure and inversely related to resistance*** - According to Ohm's law, **blood flow** is directly proportional to the **pressure gradient (perfusion pressure)** and inversely proportional to the **vascular resistance**. - This fundamental principle applies to coronary circulation, meaning higher pressure drives more flow, while higher resistance impedes it. *Coronary blood flow is inversely related to perfusion pressure and directly related to resistance* - This statement contradicts the basic principles of **fluid dynamics** and **Ohm's law**, where a higher pressure gradient generally leads to increased flow. - Direct proportionality to resistance would imply that increased obstruction leads to increased flow, which is physiologically incorrect. *Coronary blood flow is directly related to perfusion pressure and also to resistance* - While a direct relationship with **perfusion pressure** is correct, directly relating flow to **resistance** is incorrect. - Increased resistance, such as that caused by **atherosclerosis**, reduces blood flow, not increases it. *Coronary blood flow is inversely related to both pressure and resistance* - An inverse relationship with **pressure** is incorrect as an increase in the driving pressure should increase flow. - An inverse relationship with **resistance** is correct, but the inverse relationship with pressure makes the entire statement incorrect.

Question 880: Which of the following statements about volume receptors is NOT true?

A. They are located in carotid sinus (Correct Answer)
B. They are low pressure receptors
C. They mediate vasopressin release
D. They provide afferents for thirst control

Explanation: ***They are located in carotid sinus*** - Volume receptors, primarily **atrial stretch receptors** and receptors in the **pulmonary vessels**, are located in the low-pressure areas of the circulation, not the carotid sinus. - The carotid sinus primarily contains **baroreceptors** which detect changes in arterial pressure, not blood volume. *They are low pressure receptors* - This statement is true; volume receptors are indeed **low-pressure receptors** found in the atria and great veins. - They primarily monitor **extracellular fluid volume** and central venous pressure. *They provide afferents for thirst control* - This statement is true; when blood volume decreases, the firing rate of these receptors decreases, signaling the **central nervous system** to stimulate thirst. - This is an important mechanism for regulating **fluid intake** and maintaining hydration. *They mediate vasopressin release* - This statement is true; a decrease in blood volume reduces the afferent signaling from volume receptors, which consequently stimulates the release of **vasopressin (ADH)**. - Vasopressin then increases **water reabsorption** in the kidneys to conserve fluid.

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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