Circulation: A Comprehensive System of Questions and Answers

This article will provide a comprehensive and detailed understanding of the circulatory system, including questions and answers for each topic, along with important notes.

1. The sinoatrial node is the pacemaker of the entire heart because of which of the following reasons:

• A. Located in the Atria
• B. Generates nerve impulses
• C. Has a higher firing rate than other areas
• D. Under the control of the autonomic nervous system
• E. Close to the atrioventricular node

Answer: C. Has a higher firing rate than other areas

Note:

• The sinoatrial node is a specialized group of cells located in the wall of the right atrium.
• The sinoatrial node automatically generates electrical impulses at the fastest rate (approximately 60-100 times per minute) compared to other pacemaker regions in the heart.
• The sinoatrial node’s firing rate determines the normal heart rate.

2. Where is the normal pacemaker located in the human heart?

• A. Atrioventricular node
• B. Sinoatrial node
• C. Bachman’s Bundle
• D. Purkinje fibers
• E. Bundle of His

Answer: B. Sinoatrial node

Note:

• The sinoatrial node is the heart’s conduction center, initiating the electrical impulses that control the heart’s contractions.
• Other conduction centers like the atrioventricular node, Bundle of His, Bachman’s Bundle, and Purkinje fibers only play a role in transmitting electrical impulses from the sinoatrial node to other parts of the heart.

3. During the plateau phase of the ventricular action potential, which of the following channels has the highest conductance?

• A. Na+ conductance
• B. Total membrane conductance
• C. K+ conductance
• D. Ca++ conductance
• E. Cl- conductance

Answer: D. Ca++ conductance

Note:

• The plateau phase of the ventricular action potential is the phase that sustains cardiac muscle contraction.
• During this phase, Ca++ influx into cardiac muscle cells plays a primary role in maintaining the action potential.

4. The depolarization phase of the sinoatrial node cell is due to which of the following processes:

• A. Increased Na+ influx into the cell
• B. Decreased K+ efflux from the cell
• C. Increased Na+ -Ca++ exchange
• D. Decreased Cl- efflux from the cell
• E. Decreased activity of the Na+ – K+ pump

Answer: A. Increased Na+ influx into the cell

Note:

• The depolarization phase is the process of changing the cell membrane potential from its resting state to an excited state.
• In sinoatrial node cells, Na+ influx into the cell is the primary current responsible for depolarization, leading to the generation of electrical impulses.

5. Where does the action potential propagate fastest in the heart?

• A. Sinoatrial node
• B. Atrioventricular node
• C. Bundle of His
• D. Purkinje fibers
• E. Ventricular muscle

Answer: D. Purkinje fibers

Note:

• Purkinje fibers are a specialized conduction system in the heart that has the fastest conduction velocity for electrical impulses.
• Purkinje fibers enable rapid propagation of the electrical impulse from the sinoatrial node to the entire ventricular muscle, ensuring synchronous ventricular contractions.

6. Why is cardiac muscle unable to tetanize?

• A. The refractory period is long
• B. Action potentials propagate too slowly along the conduction tissue to re-excite the muscle
• C. Contraction can only occur when the heart is full of blood
• D. The sinoatrial node fires slowly
• E. The autonomic nervous system prevents the rapid propagation of action potentials

Answer: A. The refractory period is long

Note:

• The refractory period is the period during which a cardiac muscle cell cannot be re-excited, even with strong stimulation.
• The refractory period of cardiac muscle is longer than that of skeletal muscle, preventing sustained cardiac muscle contraction and ensuring a normal heart rate.

7. What cardiac abnormalities does an ECG best detect?

• A. Position of the heart in the chest
• B. Atrioventricular conduction
• C. Heart rate
• D. Cardiac contractions
• E. Coronary blood flow

Answer: B. Atrioventricular conduction

Note:

• An electrocardiogram is a technique that records the electrical activity of the heart.
• ECGs are very effective in detecting abnormalities in electrical conduction from the atria to the ventricles, such as bradycardia, arrhythmias, heart block, etc.

8. How is the P-R interval measured on an ECG?

• A. From the start of the P wave to the start of the R wave
• B. From the start of the P wave to the start of the QRS complex
• C. From the start of the P wave to the end of the QRS complex
• D. From the middle of the P wave to the start of the QRS complex
• E. From the end of the P wave to the end of the QRS complex

Answer: B. From the start of the P wave to the start of the QRS complex

Note:

• The P-R interval on an ECG reflects the time it takes for the electrical impulse to travel from the atria to the ventricles.
• The start of the P wave corresponds to the beginning of atrial contraction, while the start of the QRS complex corresponds to the beginning of ventricular contraction.

9. What is the normal duration of the P wave on an ECG?

• A. 0.08 – 0.11 seconds
• B. 0.05 – 0.08 seconds
• C. 0.08 – 0.12 seconds
• D. 0.06 – 0.11 seconds
• E. 0.05 – 0.10 seconds

Answer: A. 0.08-0.11

Note:

• The P wave on an ECG reflects atrial depolarization.
• The normal duration of the P wave is approximately 0.08 – 0.11 seconds.

10. Which of the following statements is true regarding the P-R interval on an ECG?

• A. It varies with the position of the electrode
• B. It has no physiological significance
• C. It is usually about 0.25 seconds long
• D. It is related to the conduction time from the atria to the ventricles
• E. None of the above statements are true

Answer: D. It is related to the conduction time from the atria to the ventricles

Note:

• The P-R interval reflects the time required for the electrical impulse to travel from the sinoatrial node to the ventricles.
• If the P-R interval is abnormally long, it may indicate a delay in conduction from the atria to the ventricles.

11. Which of the following is the main indicator of preload?

• A. Blood volume
• B. Central venous pressure
• C. Pulmonary capillary wedge pressure
• D. End-diastolic left ventricular volume
• E. End-diastolic left ventricular pressure

Answer: D. End-diastolic left ventricular volume

Note:

• Preload is the amount of blood in the left ventricle at the end of diastole, before the heart begins to contract.
• Preload influences the heart’s contractility.

12. Which of the following is the main indicator of afterload?

• A. End-diastolic left ventricular pressure
• B. Aortic pressure during aortic valve opening
• C. Pulmonary capillary wedge pressure
• D. Total peripheral resistance
• E. Mean arterial pressure

Answer: B. Aortic pressure during aortic valve opening

Note:

• Afterload is the resistance the heart must overcome to eject blood into the aorta.
• Afterload depends on aortic pressure and total peripheral resistance.

13. Which of the following statements is true regarding the ejection velocity of blood from the ventricle during systole?

• A. It is highest at the beginning of systole
• B. It is highest in the middle
• C. It is highest at the end
• D. It is equal throughout systole
• E. It is independent of heart rate

Answer: A. It is highest at the beginning of systole

Note:

• The ejection velocity of blood from the ventricle during systole is fastest at the beginning of systole, then decreases gradually.
• The change in ejection velocity depends on the pressure in the ventricle and the aorta.

14. Which of the following statements is true regarding the rate of blood flow into the ventricle during diastole?

• A. It is constant throughout diastole
• B. It is highest at the beginning
• C. It is highest in the middle
• D. It is highest at the end
• E. It varies according to atrial contraction time

Answer: B. It is highest at the beginning

Note:

• The rate of blood flow into the ventricle during diastole is fastest at the beginning of diastole, then decreases gradually.
• The change in blood flow rate into the ventricle depends on the pressure in the veins and the pressure in the ventricle.

15. When does the second heart sound occur?

• A. Isometric contraction
• B. Isovolumetric contraction
• C. Isometric relaxation
• D. Isovolumetric relaxation
• E. None of the above statements are true

Answer: E. None of the above statements are true

Note:

• The second heart sound is the sound of the aortic and pulmonary valves closing.
• The second heart sound occurs at the beginning of ventricular relaxation, when the pressure in the ventricle is lower than the pressure in the aorta and pulmonary artery.

16. What initiates the closure of the atrioventricular valves?

• A. Atrial contraction
• B. Ventricular contraction
• C. Papillary muscle contraction
• D. Ventricular relaxation
• E. Ventricular pressure exceeding atrial pressure

Answer: E. Ventricular pressure exceeding atrial pressure

Note:

• Atrioventricular valve closure occurs when the pressure in the ventricle exceeds the pressure in the atrium.
• As the ventricle contracts, the pressure inside increases, pushing the atrioventricular valves shut.

17. What occurs after the first heart sound and before the second heart sound?

• A. The heart’s ejection phase
• B. The P wave of the ECG
• C. Isovolumetric relaxation
• D. Atrial contraction
• E. The heart filling with blood

Answer: A. The heart’s ejection phase

Note:

• The first heart sound is the sound of the atrioventricular valves closing.
• The second heart sound is the sound of the aortic and pulmonary valves closing.
• The heart’s ejection phase is the period during which the heart contracts and pushes blood out of the ventricles.

18. During the ejection phase, where is the pressure difference smallest?

• A. Pulmonary artery and left atrium
• B. Right ventricle and right atrium
• C. Left ventricle and aorta
• D. Left ventricle and left atrium
• E. Aorta and capillaries

Answer: C. Left ventricle and aorta

Note:

• Pressure difference is the difference in pressure between two points.
• During the ejection phase, the pressure in the left ventricle is almost equal to the pressure in the aorta, so the pressure difference between these two locations is minimal.

19. During rest, how many liters of blood does a healthy male pump in a minute?

• A. 0.9
• B. 2 to 3
• C. 5 to 6
• D. 8 to 10
• E. 15 to 20

Answer: C. 5 to 6

Note:

• Cardiac output is the amount of blood the heart pumps out in a minute.
• At rest, the cardiac output of a healthy male is approximately 5-6 liters/minute.

20. In an individual, oxygen consumption is measured at 700 ml/minute, pulmonary artery oxygen content is 140 ml/liter of blood, and systemic arterial oxygen content is 210 ml/liter of blood. What is the cardiac output?

• A. 4.2 L/minute
• B. 7.0 L/minute
• C. 10.0 L/minute
• D. 12.6 L/minute
• E. 30.0 L/minute

Answer: C. 10.0 L/minute

Note:

• Oxygen consumption is the amount of oxygen the body utilizes in a minute.
• Cardiac output can be calculated using the formula: Cardiac output = Oxygen consumption / (Systemic arterial oxygen content – Pulmonary artery oxygen content).

21. Increased stimulation of the vagus nerve will enhance which of the following activities?

• A. Heart rate
• B. Cardiac contractility
• C. Cardiac conduction
• D. Acetylcholine secretion
• E. Norepinephrine secretion

Answer: D. Acetylcholine secretion

Note:

• The vagus nerve is a parasympathetic nerve that slows heart rate and reduces cardiac contractility.
• Increased vagus nerve stimulation will increase acetylcholine secretion, a parasympathetic neurotransmitter.

22. Which of the following accurately describes the effect of respiration on heart rate?

• A. Heart rate decreases during inspiration and increases during expiration
• B. Heart rate increases during inspiration and decreases during expiration
• C. Heart rate increases during inspiration and increases during expiration
• D. Heart rate decreases during inspiration and decreases during expiration
• E. None of the above statements are true

Answer: B. Heart rate increases during inspiration and decreases during expiration

Note:

• Respiration influences heart rate, known as the respiratory-heart reflex.
• During inspiration, intrathoracic pressure decreases, stimulating pressure receptors, which leads to an increase in heart rate.
• During expiration, intrathoracic pressure increases, inhibiting pressure receptors, leading to a decrease in heart rate.

23. What is the effect of the ventricular receptor reflex?

• A. Decreases heart rate and decreases peripheral resistance
• B. Increases heart rate and increases peripheral resistance
• C. Decreases heart rate and increases peripheral resistance
• D. Increases heart rate and decreases peripheral resistance
• E. None of the above statements are true

Answer: A. Decreases heart rate and decreases peripheral resistance

Note:

• The ventricular receptor reflex is the Frank-Starling reflex.
• This reflex helps regulate blood flow back to the heart.
• When ventricular blood volume increases, ventricular receptors are stimulated, leading to a decrease in heart rate and vasodilation, which reduces peripheral resistance and facilitates blood return to the heart.

24. What is the consequence of elevated epinephrine levels in the blood?

• A. Decreases stroke volume
• B. Decreases heart rate
• C. Increases cardiac output
• D. Decreases cardiac contractility
• E. Decreases cardiac conduction

Answer: C. Increases cardiac output

Note:

• Epinephrine is a hormone secreted by the adrenal glands that stimulates the sympathetic nervous system.
• Increased epinephrine levels in the blood increase heart rate, enhance cardiac contractility, and ultimately lead to an increase in cardiac output.

25. When does the amount of blood ejected from the heart in a single beat increase in a normal person?

• A. Increased sympathetic stimulation to the heart
• B. Increased parasympathetic stimulation to the heart
• C. Decreased contractility
• D. Decreased end-diastolic volume
• E. Baroreceptor reflex

Answer: A. Increased sympathetic stimulation to the heart

Note:

• Increased sympathetic stimulation to the heart increases heart rate, enhances cardiac contractility, and ultimately leads to an increase in the amount of blood ejected in a single beat.

26. Sympathetic effects:

• A. Right sympathetic stimulation has a greater effect on contractility than on heart rate
• B. Left sympathetic stimulation has a greater effect on contractility than on heart rate
• C. Right and left sympathetic stimulation have the same effect on contractility
• D. Right and left sympathetic stimulation have the same effect on heart rate
• E. None of the above statements are true

Answer: B. Left sympathetic stimulation has a greater effect on contractility than on heart rate

Note:

• Left sympathetic stimulation has a greater effect on increasing the contractility of the left ventricle than on increasing heart rate.

27. The increase in contractility that occurs when the interval between beats is suddenly shortened is due to:

• A. Gradual increase in intracellular Na+ concentration
• B. Gradual increase in intracellular K+ concentration
• C. Gradual increase in intracellular Ca++ concentration
• D. Gradual increase in intracellular Cl- concentration
• E. None of the above statements are true

Answer: C. Gradual increase in intracellular Ca++ concentration

Note:

• Increased contractility is an increase in the force of cardiac muscle contraction.
• When the interval between beats is suddenly shortened, Ca++ levels in cardiac muscle cells accumulate, leading to increased contractility.

28. On cardiac muscle cell membranes, acetylcholine acts on:

• A. Muscarinic receptors
• B. Nicotinic receptors
• C. Muscarinic and nicotinic receptors
• D. No effect on receptors
• E. Stimulates adenyl cyclase

Answer: A. Muscarinic receptors

Note:

• Acetylcholine is a parasympathetic neurotransmitter.
• Acetylcholine acts on muscarinic receptors on cardiac muscle cell membranes, reducing heart rate and cardiac contractility.

29. Decreased oxygen in the blood:

• A. Increases cardiac contractility
• B. Decreases cardiac contractility
• C. Has no effect on cardiac contractility
• D. Only affects heart rate
• E. Two-phase effect: low oxygen stimulation, high oxygen inhibition

Answer: A. Increases cardiac contractility

Note:

• Decreased oxygen in the blood stimulates the heart.
• Hypoxia increases epinephrine secretion, leading to enhanced cardiac contractility.

30. Consider the components of the baroreceptor reflex and indicate what happens when blood pressure increases:

• A. Stimulates baroreceptors
• B. Inhibits baroreceptors
• C. Increases sympathetic activity to the heart
• D. Increases arteriolar tone
• E. Increases venous tone

Answer: B. Inhibits baroreceptors

Note:

• Baroreceptors are receptors that sense changes in blood pressure.
• When blood pressure increases, baroreceptors are inhibited, leading to decreased sympathetic activity to the heart, vasodilation, and ultimately reducing blood pressure to normal levels.

31. If the resting diameter of a blood vessel decreases by half, how many times does the resistance to blood flow increase?

• A. 2
• B. 4
• C. 8
• D. 12
• E. 16

Answer: E. 16

Note:

• Blood vessel resistance is inversely proportional to the square of the blood vessel diameter.
• If the blood vessel diameter decreases by half, the resistance to blood flow will increase 16 times.

32. What factors influence blood viscosity?

• A. Erythrocyte sedimentation rate
• B. Number of blood cells
• C. Shape of blood cells
• D. Plasma protein content
• E. All of the above statements are true

Answer: E. All of the above statements are true

Note:

• Blood viscosity is a measure of blood thickness.
• Blood viscosity is influenced by several factors, including: the number of blood cells, the shape of blood cells, the concentration of proteins in plasma, etc.

33. Which of the following is NOT a factor that determines blood flow?

• A. Pressure difference
• B. Blood vessel diameter
• C. Blood pH
• D. Total peripheral resistance
• E. Arterial wall elasticity

Answer: C. Blood pH

Note:

• Blood flow is the volume of blood flowing through a blood vessel in a given time.
• Blood pH influences vasoconstriction or vasodilation, but it is not a primary factor in determining blood flow.

34. Where is the blood volume highest in the circulatory system?

• A. Arteries
• B. Capillaries
• C. Veins
• D. Venous sinuses
• E. None of the above statements are true

Answer: C. Veins

Note:

• Veins have thin, elastic walls, allowing them to hold more blood than arteries.

35. In the circulatory system, when vessels are connected in parallel:

• A. Total resistance equals the sum of individual resistances
• B. Total resistance equals the sum of resistances of each part
• C. Total resistance is less than the resistance of each part
• D. None of the above statements are true
• E. There is no resistance in a parallel connection

Answer: C. Total resistance is less than the resistance of each part

Note:

• When vessels are connected in parallel, the total resistance of the circulatory system is less than the resistance of each individual vessel.
• This is because blood has multiple pathways to flow through, reducing overall resistance.

36. When does vascular resistance increase?

• A. When blood cells decrease
• B. When white blood cells increase
• C. When blood cells increase
• D. When plasma protein content decreases
• E. When platelets decrease

Answer: C. When blood cells increase

Note:

• When the number of blood cells in the blood increases, blood viscosity increases, leading to increased vascular resistance.

37. Closing pressure is:

• A. When blood pressure is zero
• B. When the vessel collapses and blood pressure is zero
• C. When the vessel collapses and blood pressure is not zero
• D. When the vessel is not collapsed and blood pressure is zero
• E. None of the above statements are true

Answer: C. When the vessel collapses and blood pressure is not zero

Note:

• Closing pressure is the minimum blood pressure required to