Cardiovascular System Practice Questions

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.

Q: Vagal stimulation of the heart causes

Increased R-R interval in ECG. ***Increased R-R interval in ECG*** - Vagal stimulation releases **acetylcholine**, which acts on **M2 muscarinic receptors** in the heart, particularly in the SA and AV nodes. - This leads to a decrease in heart rate, which manifests as an **increase in the R-R interval** on an ECG. *Increased heart rate* - Vagal stimulation is part of the **parasympathetic nervous system**, which generally **decreases heart rate**. - **Sympathetic stimulation**, not vagal stimulation, is responsible for increasing heart rate. *Increased force of heart contraction* - While vagal innervation affects atrial contractility, its primary effect on ventricular contractility is minimal compared to **sympathetic stimulation**. - Increased force of contraction is mainly mediated by **catecholamines** from the sympathetic nervous system. *Increased cardiac output* - Cardiac output is the product of heart rate and stroke volume; a decrease in heart rate due to vagal stimulation would generally **decrease cardiac output**, assuming stroke volume remains constant or does not significantly increase to compensate. - Vagal stimulation primarily aims to **conserve energy** and *slow down heart activity*, not increase overall output.

Q: What is the primary cardiovascular compensatory mechanism in acute hemorrhage?

Increased heart rate. ***Increased heart rate*** - In acute hemorrhage, the body senses a decrease in **blood volume** and **blood pressure**, triggering the **baroreceptor reflex**. - This reflex leads to increased sympathetic nervous system activity, causing an immediate compensatory **increase in heart rate** to maintain **cardiac output** and tissue perfusion. *Decreased myocardial contractility* - A decrease in myocardial contractility would worsen the situation in hemorrhage by further reducing **cardiac output** and is not a primary compensatory mechanism. - While prolonged severe hemorrhage can lead to myocardial depression due to ischemia, it is a pathological consequence, not a compensatory response. *Decreased heart rate* - A decrease in heart rate would reduce **cardiac output** and further compromise blood flow to vital organs during hemorrhage, which is precisely the opposite of what the body needs. - This response is usually seen with vagal stimulation, not in response to hypovolemic shock. *Increased respiratory rate* - An **increased respiratory rate** is a compensatory mechanism for conditions like **metabolic acidosis** (which can occur in severe shock due to lactic acid accumulation) or to improve oxygenation, but it is not the primary cardiovascular compensatory mechanism for maintaining blood pressure and cardiac output in acute hemorrhage. - While it often accompanies hemorrhage, it acts to regulate oxygen and CO2 levels, not directly blood volume or pressure.

Q: What is the normal range for portal vein pressure?

5-10 mm Hg. ***5-10 mm Hg*** - The normal **portal vein pressure** typically ranges from 5 to 10 mmHg. - Pressures above this range are indicative of **portal hypertension**, a common complication of **cirrhosis** and other liver diseases, which can lead to varices and ascites. *1-3 mm Hg* - This range is significantly lower than the **normal portal vein pressure**. - Such low pressures are not typically observed in the **portal venous system** under normal physiological conditions. *3-5 mm Hg* - This range is still considered to be on the lower end and borders on **hypotension** within the portal system. - While it's relatively close to the lower limit of normal, it doesn't represent the typical **physiological range** of portal vein pressure. *10-15 mm Hg* - Pressures in this range are usually considered **elevated** and fall within the spectrum of **portal hypertension**. - While slight elevations might occur transiently, a sustained pressure in this range indicates an underlying issue, such as **cirrhosis** or **post-hepatic obstruction**.

Q: Depolarization of the ventricular muscles starts at which site?

Left side of the interventricular septum. ***Left side of the interventricular septum*** - The **Purkinje fibers** rapidly transmit the electrical impulse down the **Bundle of His** and then branch out to depolarize the myocardium. - Depolarization typically begins on the left side of the **interventricular septum**, spreading outwards and upwards. *Right side of the septum* - While the septum depolarizes, the earliest activation generally initiates on the **left septal wall**, not the right. - The spread of activation from the right side of the septum occurs slightly later than from the left because the left bundle branch is shorter and reaches the septum more quickly, establishing earlier depolarization. *Apex of the heart* - Although the Purkinje fibers extend towards the apex, the initial site of ventricular depolarization is the **septum**, not the apex itself. - Depolarization then proceeds from the septum towards the apex and the ventricular free walls. *AV groove* - The **AV groove** is the junction between the atria and ventricles, containing the **AV node**. - The **AV node** delays propagation, but ventricular depolarization originates from the **His-Purkinje system** beyond the AV node, specifically in the septum.

Q: Function of phospholamban is

Regulates calcium uptake by inhibiting SERCA. ***Regulates calcium uptake by inhibiting SERCA*** - **Phospholamban (PLN)** is a **regulatory protein** that, in its unphosphorylated state, **inhibits the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA)** pump. - This inhibition reduces the rate of **calcium reuptake** into the sarcoplasmic reticulum, thus influencing myocardial relaxation and contractility. - When phosphorylated by **protein kinase A (PKA)** or **CaMKII**, phospholamban's inhibition is relieved, allowing increased calcium uptake. *Regulates sodium and potassium levels* - The regulation of **sodium and potassium levels** is primarily mediated by the **Na+/K+-ATPase pump**, which is distinct from phospholamban's function. - Phospholamban's role is specifically in **calcium handling** within the sarcoplasmic reticulum, particularly in cardiomyocytes. *Transports calcium out of the cell* - Transport of **calcium out of the cell** is primarily performed by the **plasma membrane Ca2+-ATPase (PMCA)** and the **Na+/Ca2+ exchanger (NCX)**. - **SERCA**, which phospholamban regulates, pumps calcium **into the sarcoplasmic reticulum**, not out of the cell. - Phospholamban modulates SERCA activity but does not directly transport calcium itself. *Binds to actin and myosin* - **Actin and myosin** are the primary contractile proteins involved in muscle contraction. - Proteins like **troponin and tropomyosin** bind to these contractile proteins to regulate contraction, whereas phospholamban is a **regulatory protein** affecting calcium handling in the sarcoplasmic reticulum.

Q: What is the reason for the higher V wave in the left atrium compared to the right atrium?

Lower compliance (higher stiffness) of the left atrium.. ***Lower compliance (higher stiffness) of the left atrium.*** - The **left atrium** typically has **lower compliance** (higher stiffness) than the right atrium. - This anatomical difference means that for the same volume of blood return, the pressure increase (and thus the **V wave**) in the less compliant left atrium will be greater than in the more compliant right atrium. *Increased blood return to the left atrium from the pulmonary veins.* - While the **left atrium** receives a significant volume of blood from the **pulmonary veins**, the absolute volume of blood return alone doesn't explain the *higher V wave* relative to the right atrium unless compounded by compliance differences. - The overall cardiac output is the same for both sides of the heart; therefore, the absolute blood return to both atria is roughly equal over time. *The right atrium receives more blood.* - The **right atrium** receives venous blood from the **superior and inferior vena cava**, representing the entire systemic circulation. - The **left atrium** receives blood from the pulmonary circulation, and in a healthy individual, the **cardiac output** is the same for both ventricles, implying equal venous return to both atria over cycles. *Decreased blood return to the left atrium from the pulmonary veins.* - **Decreased blood return** would lead to a *lower V wave* (lower pressure) in the left atrium, not a higher one. - A higher V wave indicates increased volume or pressure during atrial filling.

Q: Which of the following structures in the heart are known for their rapid conduction of electrical impulses?

Purkinje fibers. ***Correct: Purkinje fibers*** - **Purkinje fibers** have the **fastest conduction velocity** among all cardiac tissues, approximately **4 m/s** - These specialized myocardial fibers ensure **rapid and synchronized depolarization of the ventricles**, allowing for efficient and coordinated ventricular contraction - Their rapid conduction is essential for simultaneous contraction of ventricular myocardium from apex to base *Incorrect: Sinoatrial (SA) node* - The SA node is the natural **pacemaker** of the heart, initiating electrical impulses at a rate that determines heart rate - However, its conduction velocity is **very slow** (~0.05 m/s), much slower than Purkinje fibers - Its role is impulse generation, not rapid conduction *Incorrect: Atrioventricular (AV) node* - The AV node has the **slowest conduction velocity** in the heart (~0.05 m/s) - It **delays electrical impulses** from the atria to the ventricles (AV delay ~0.1 seconds) - This delay allows for **complete ventricular filling** before ventricular contraction begins *Incorrect: His bundle* - The bundle of His transmits impulses from the AV node to the bundle branches - While faster than the AV node (~1-1.5 m/s), it is still **significantly slower than Purkinje fibers** - Its conduction velocity is intermediate between the AV node and Purkinje fibers

Q: Cardiac hyperaemia/vasodilation is due to which mediator?

Adenosine. ***Adenosine*** - **Adenosine** is a potent endogenous vasodilator in the heart, released in response to increased myocardial oxygen demand or ischemia. - It acts on **A2A receptors** in vascular smooth muscle, leading to relaxation and increased coronary blood flow (hyperemia). *Acetylcholine* - **Acetylcholine** primarily causes vasodilation in skeletal muscle and some other vascular beds, mediated by nitric oxide release from endothelial cells. - In the heart, it mainly acts as a **negative chronotropic** and **dromotropic** agent, slowing heart rate and conduction, with variable direct effects on coronary vessels. *Adrenaline* - **Adrenaline** (epinephrine) typically causes vasoconstriction via **alpha-1 receptors** in many vascular beds, but can cause vasodilation via **beta-2 receptors** in some, such as skeletal muscle. - In the heart, its primary effect is positive chronotropy and inotropy, and it can cause **coronary vasoconstriction** or dilation depending on receptor distribution and dose. *Dopamine* - **Dopamine** has complex effects on the vasculature, depending on the dose and receptor subtypes activated. - At low doses, it can cause **renal and mesenteric vasodilation** via D1 receptors, but at higher doses, it can cause generalized vasoconstriction via alpha-adrenergic receptors.

Question 1

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

Question 2

Vagal stimulation of the heart causes

Accepted Answer

Increased R-R interval in ECG

Answer

Increased cardiac output

Answer

Increased heart rate

Answer

Increased force of heart contraction

Question 3

What is the primary cardiovascular compensatory mechanism in acute hemorrhage?

Accepted Answer

Increased heart rate

Answer

Decreased myocardial contractility

Answer

Increased respiratory rate

Answer

Decreased heart rate

Question 4

What is the normal range for portal vein pressure?

Accepted Answer

5-10 mm Hg

Answer

1-3 mm Hg

Answer

3-5 mm Hg

Answer

10-15 mm Hg

Question 5

What characterizes the plateau (phase 2) of the ventricular myocyte action potential?

Accepted Answer

Describes when Ca2+ influx is balanced by K+ efflux, with Na+ channels inactivated.

Answer

Describes when Ca2+ influx is predominant but K+ efflux is also significant.

Answer

Describes when Ca2+ influx is balanced by K+ efflux.

Answer

Can be influenced by sympathetic nerve stimulation.

Question 6

Depolarization of the ventricular muscles starts at which site?

Accepted Answer

Left side of the interventricular septum

Answer

Right side of the septum

Answer

Apex of the heart

Answer

AV groove

Question 7

Function of phospholamban is

Accepted Answer

Regulates calcium uptake by inhibiting SERCA

Answer

Regulates sodium and potassium levels

Answer

Transports calcium out of the cell

Answer

Binds to actin and myosin

Question 8

What is the reason for the higher V wave in the left atrium compared to the right atrium?

Accepted Answer

Lower compliance (higher stiffness) of the left atrium.

Answer

The right atrium receives more blood.

Answer

Increased blood return to the left atrium from the pulmonary veins.

Answer

Decreased blood return to the left atrium from the pulmonary veins.

Question 9

Which of the following structures in the heart are known for their rapid conduction of electrical impulses?

Accepted Answer

Purkinje fibers

Answer

Sinoatrial (SA) node

Answer

Atrioventricular (AV) node

Answer

His bundle

Question 10

Cardiac hyperaemia/vasodilation is due to which mediator?

Accepted Answer

Adenosine

Answer

Acetylcholine

Answer

Adrenaline

Answer

Dopamine

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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