Cardiovascular Physiology – Knowledge Supplement

I. Cardiac Conduction System

• The normal sinoatrial node is the pacemaker of the entire heart because:
  • Higher impulse rate than other sites: The sinoatrial node has the highest intrinsic impulse rate (60-100 beats/minute), faster than the atrioventricular node (40-60 beats/minute) and the His-Purkinje system (20-40 beats/minute).
    Note: If the sinoatrial node is damaged, other nodes can take over the pacemaker function, but the heart rate will be slower.
• The location of the normal pacemaker in the human heart is:
  • Sinoatrial node: The sinoatrial node is located in the right atrial wall, near the junction of the superior vena cava and the right atrium.
    Note: This is where the electrical impulse originates and is transmitted to the entire heart.
• In the Plateau Phase of the ventricular action potential, which channel’s conductance is the greatest:
  • Ca++ conductance: During the plateau phase, the Ca++ channel is open, allowing Ca++ from outside the cell to enter the cell, maintaining muscle contraction.
    Note: This phase plays a vital role in the mechanism of muscle contraction.
• Where does the cardiac action potential propagate the fastest:
  • Purkinje fibers: Purkinje fibers have the fastest conduction velocity (1.5-4 m/s) in the cardiac conduction system, allowing the electrical impulse to travel quickly to the ventricles, ensuring synchronized ventricular contraction.
    Note: This is a specialized conduction system that helps to ensure the contraction of the ventricles is uniform and efficient.
• The depolarization phase of the sinoatrial nodal cell is due to which process:
  • Increased Na+ influx into the cell: The depolarization phase of the sinoatrial nodal cell is due to Na+ influx into the cell, causing the membrane potential to change from negative to positive.
    Note: This is the process that generates the electrical impulse in the sinoatrial node, initiating the cardiac cycle.

II. Cardiac Muscle Function

• Cardiac muscle cannot contract in a tetanus-like manner because:
  • Long absolute refractory period: The absolute refractory period of cardiac muscle is long, preventing the muscle from contracting again while it is contracting.
    Note: This helps the heart to contract rhythmically and efficiently, preventing tetanic contraction.
• An electrocardiogram is most useful in detecting abnormalities in:
  • Heart rhythm: An electrocardiogram is a useful tool for assessing heart rhythm, detecting rhythm abnormalities such as tachycardia, bradycardia, and arrhythmias.
    Note: An electrocardiogram can help diagnose diseases related to the cardiac conduction system.
• An electrocardiogram is least effective in detecting abnormalities in:
  • Coronary blood flow: An electrocardiogram cannot directly assess coronary blood flow.
    Note: To assess coronary blood flow, specialized techniques such as coronary angiography are required.
• The normal duration of the P wave:
  • 0.08-0.11 seconds: The P wave on an electrocardiogram represents atrial depolarization, and the normal duration of the P wave is 0.08-0.11 seconds.
    Note: A prolonged P wave duration may be a sign of atrial disease.
• Which of the following statements about the P-R interval on an electrocardiogram is correct:
  • It relates to the time of conduction from the atria to the ventricles: The P-R interval represents the time it takes for the electrical impulse to travel from the atria to the ventricles, including the time of atrial depolarization and the time of conduction through the atrioventricular node.
    Note: An abnormal P-R interval may be a sign of cardiac conduction disease.
• The normal P-R interval has a duration of:
  • 0.12-0.2 seconds: The normal P-R interval is 0.12-0.2 seconds.
    Note: A shorter or longer P-R interval may be a sign of cardiac disease.
• The repolarization of the ventricles is represented by which wave:
  • T wave: The T wave on an electrocardiogram represents ventricular repolarization, the return of the heart muscle to its resting state.
    Note: An abnormal T wave may be a sign of cardiovascular disease.

III. Cardiac Cycle

• What factor is the main indicator of preload:
  • End-diastolic left ventricular volume: Preload is the stretch of the heart muscle before contraction, determined by the volume of blood in the left ventricle at the end of diastole.
    Note: A higher preload leads to a stronger heart contraction.
• Which of the following is the main indicator of afterload:
  • Aortic pressure during aortic valve opening: Afterload is the resistance the heart must overcome to eject blood into the aorta, determined by the aortic pressure during aortic valve opening.
    Note: A higher afterload leads to a stronger heart contraction, but also makes the heart work harder.
• The aortic valve closes at the beginning of which phase of the cardiac cycle:
  • Isovolumetric relaxation: The aortic valve closes at the beginning of the isovolumetric relaxation phase, when the pressure in the left ventricle falls below the pressure in the aorta.
    Note: Isovolumetric relaxation is the phase when the ventricle relaxes but the volume of blood in the ventricle does not change.
• The rate of blood ejection from the ventricle during systole is:
  • Highest in the first 1/3 of systole: The rate of blood ejection from the ventricle is highest in the first 1/3 of systole, then gradually decreases.
    Note: This is related to the change in pressure in the left ventricle throughout the contraction process.
• The closure of the atrioventricular valve is initiated by:
  • Ventricular pressure exceeding atrial pressure: When the ventricle contracts, the pressure in the ventricle increases, exceeding the pressure in the atrium, causing the atrioventricular valve to close.
    Note: This process prevents backflow of blood from the ventricle to the atrium.
• The second heart sound occurs during:
  • Isovolumetric relaxation: The second heart sound occurs during isovolumetric relaxation, when the aortic valve closes.
    Note: The second heart sound is often described as the “dub” sound.
• The event that occurs after the first heart sound and before the second heart sound:
  • Ventricular ejection: After the first heart sound, the ventricle contracts and ejects blood into the aorta.
    Note: This is the main work phase of the heart, generating blood pressure.
• The amount of blood pumped by the heart with each beat is reduced by:
  • Decreased blood pressure: Decreased blood pressure leads to a decrease in the amount of blood pumped with each beat.
    Note: This is related to the Frank-Starling law, the heart contracts more strongly when preload is higher.
• What increases when parasympathetic stimulation increases:
  • Acetylcholine secretion: Parasympathetic stimulation leads to acetylcholine secretion, slowing down the heart rate and reducing heart contractility.
    Note: The parasympathetic system has an opposite effect to the sympathetic system, helping the body return to a resting state.
• Which of the following increases during exercise:
  • Cardiac output: During exercise, cardiac output increases to provide enough oxygen and nutrients to the body.
    Note: Cardiac output is the amount of blood pumped by the heart in one minute.
• Increased stimulation of the vagus nerve will increase the activity of:
  • Acetylcholine secretion: The vagus nerve (parasympathetic nerve) will increase acetylcholine secretion, slowing down the heart rate.
    Note: The vagus nerve is part of the parasympathetic nervous system.
• The correct statement describing the effect of respiration on heart rate:
  • Heart rate increases during inspiration and decreases during expiration: During inspiration, the pressure in the chest cavity decreases, increasing heart rate; during expiration, the pressure in the chest cavity increases, decreasing heart rate.
    Note: This is called the respiratory sinus arrhythmia.
• The reflex from receptors in the ventricles has the effect of:
  • Decreasing heart rate and decreasing peripheral resistance: Receptors in the ventricles sense the stretch of the ventricles, when the ventricles are stretched excessively, the reflex will lead to a decrease in heart rate and a decrease in peripheral resistance.
    Note: This reflex helps regulate the activity of the heart and blood vessels to maintain stable blood pressure.

IV. Blood Pressure and Blood Flow

• Increased epinephrine levels cause:
  • Increased cardiac output: Epinephrine (Adrenaline) is a hormone secreted from the adrenal gland, which increases heart rate, increases heart contractility, leading to an increase in cardiac output.
    Note: Epinephrine is a sympathetic stimulant.
• In a normal person, the amount of blood pumped by the heart with each beat increases under what conditions:
  • Increased sympathetic stimulation to the heart: Sympathetic stimulation leads to an increase in heart rate, an increase in heart contractility, leading to an increase in the amount of blood pumped by the heart with each beat.
    Note: The sympathetic system has an effect of increasing heart activity.
• Which of the following is not a factor that determines blood flow:
  • Blood pH: Blood pH is not a factor that determines blood flow.
    Note: Blood pH affects gas exchange, but does not affect blood flow.
• Blood viscosity depends on:
  • All of the above: Blood viscosity depends on several factors, including:
    • Red blood cell concentration: Red blood cells are the main factor contributing to blood viscosity.
    • Plasma protein concentration: Plasma proteins also contribute to blood viscosity.
    • Temperature: High temperatures decrease blood viscosity.

    Note: Blood viscosity affects blood flow.

• The least important characteristic of the vessel wall:
  • Multiple nerve endings: The vessel wall may have multiple nerve endings, but this is not the most important characteristic of the vessel wall.
    Note: The vessel wall has many other important characteristics such as elasticity, thickness, and the presence of smooth muscle.
• Factors that cause a decrease in arterial pressure:
  • Decreased blood volume: Decreased blood volume leads to a decrease in arterial pressure.
    Note: This is related to the basic principle of blood pressure: pressure is directly proportional to volume.
• Factors that increase arterial pressure EXCEPT:
  • Increased vessel wall elasticity: Increased vessel wall elasticity leads to a decrease in arterial pressure.
    Note: Vessel wall elasticity helps maintain stable blood flow.
• The exchange of nutrients between blood and tissues occurs in:
  • Capillaries: Capillaries are the smallest blood vessels, with thin walls and a function of exchanging nutrients between blood and tissues.
    Note: Capillaries are an important bridge between blood and cells.
• The greatest total surface area of blood vessels is in:
  • Capillaries: Capillaries have the greatest total surface area of blood vessels, increasing the surface area of contact with cells, enhancing exchange.
    Note: A larger total surface area of blood vessels means more efficient exchange.
• The largest percentage of blood volume is located in:
  • Venules and veins: Venules and veins contain the largest amount of blood (about 60-65% of the total blood volume in the body).
    Note: This is an important blood reserve for the body.
• Which statement is correct about autoregulation due to muscle in the vessels:
  • When the pressure in the vessel increases, the vessel constricts, and vice versa: When the pressure in the vessel increases, the smooth muscle in the vessel wall contracts, narrowing the lumen, reducing blood flow; when the pressure in the vessel decreases, the smooth muscle relaxes, widening the lumen, increasing blood flow.
    Note: The autoregulation mechanism helps maintain stable blood flow at a level appropriate for the needs of the tissue.
• The nervous regions involved in the vascular reflex:
  • All of the above statements are correct: The nervous regions involved in the vascular reflex include:
    • The vasomotor center in the spinal cord: Controls vasoconstriction and vasodilation.
    • The vasomotor center in the brainstem: Controls heart rate and vascular resistance.
    • The cerebral cortex: Can control the vascular reflex consciously.

    Note: The vascular nervous system is complex, with many nervous regions involved.

• The baroreceptor reflex has the effect of:
  • Slowing down the heart rate and causing vasodilation: The baroreceptor reflex senses changes in blood pressure, when blood pressure increases, the reflex will lead to a decrease in heart rate and vasodilation, helping to reduce blood pressure to normal levels.
    Note: The baroreceptor reflex is an important mechanism that helps maintain stable blood pressure.
• The chemoreceptor reflex causes:
  • Vasoconstriction: When chemoreceptors are stimulated, the reflex will lead to vasoconstriction, helping to increase blood pressure.
    Note: This reflex is triggered by chemicals such as adrenaline and norepinephrine.
• Decreased pressure in the carotid sinus will decrease:
  • Stimulation of the cardiac inhibitory center: Decreased pressure in the carotid sinus will decrease the stimulation of the cardiac inhibitory center, leading to an increase in heart rate.
    Note: The carotid sinus is part of the baroreceptor system, helping to regulate blood pressure.
• When the pressure receptors are reduced in stimulation, the factors increase EXCEPT:
  • Parasympathetic nerve activity: When the pressure receptors are reduced in stimulation, the reflex will lead to an increase in sympathetic nerve activity, reducing parasympathetic nerve activity.
    Note: This reflex helps increase blood pressure.
• Increased preload is mainly due to an increase in:
  • Venous tone: Increased venous tone leads to an increase in the amount of blood returning to the heart, increasing preload.
    Note: Preload is the amount of blood in the left ventricle at the end of diastole.
• The factor that creates the first heart sound is:
  • Closure of the atrioventricular valves: The first heart sound is created by the closure of the atrioventricular valves, when the ventricle contracts.
    Note: The first heart sound is often described as the “lub” sound.
• The left ventricle has a thicker wall than the right ventricle because:
  • The left ventricle pumps blood at a higher pressure: The left ventricle must pump blood into the aorta at a higher pressure than the right ventricle pumps blood into the pulmonary artery, so the left ventricle has a thicker wall.
    Note: This is an anatomical adaptation that helps the heart work more efficiently.
• The factor that creates the second heart sound:
  • Closure of the semilunar valves: The second heart sound is created by the closure of the semilunar valves, when the ventricle relaxes.
    Note: The second heart sound is often described as the “dub” sound.
• Cardiac stimulation can only cause a response when:
  • Stimulation reaches threshold and is in the relative refractory period: Cardiac stimulation can only cause a response when stimulation reaches threshold and is in the relative refractory period.
    Note: This is the “all-or-none” law in the mechanism of heart muscle contraction.
• The ventricular systole phase is correct with:
  • Closure of the atrioventricular valves and opening of the aortic valve: The ventricular systole phase is the phase when the ventricle contracts, closes the atrioventricular valve and opens the aortic valve, pumping blood into the aorta.
    Note: This phase is the phase when the heart pumps blood out of the heart.
• The chamber of the heart that plays the main role in the cardiac cycle is:
  • The entire ventricle: The ventricles are the chambers of the heart that play the main role in the cardiac cycle, responsible for pumping blood into the circulatory system.
    Note: The atria play the role of receiving blood from the veins and transmitting electrical impulses to the ventricles.
• What is happening when you hear the second heart sound:
  • Ventricular relaxation, atrial relaxation: When you hear the second heart sound, the ventricle is relaxing, the atrium is relaxing to receive blood from the veins.
    Note: This is the end phase of the cardiac cycle.
• What is happening when you hear the first heart sound:
  • Atrial relaxation, ventricular contraction: When you hear the first heart sound, the atrium is relaxing, the ventricle is contracting.
    Note: This is the beginning phase of the cardiac cycle.
• Cardiac muscle is characterized by the properties of:
  • Both A and B (syncytium and very fast electrical potential conduction through gap junctions): Cardiac muscle has the property of syncytium, cardiac muscle cells are connected to each other to form a network, allowing electrical potential to travel quickly between cells, helping the heart to contract uniformly.
    Note: This is a unique characteristic of cardiac muscle compared to skeletal muscle and smooth muscle.
• The cause of the closure of the bicuspid and tricuspid valves:
  • Pressure difference between the atrium and ventricle: The bicuspid valve (mitral valve) and the tricuspid valve close when the pressure in the ventricle is higher than the pressure in the atrium.
    Note: This prevents backflow of blood from the ventricle to the atrium.
• In the cardiac cycle, the period from the beginning of closure of the atrioventricular valve to the closure of the semilunar valve corresponds to which phase:
  • Statements B and C are correct (atrial relaxation and ventricular systole): The period from the beginning of closure of the atrioventricular valve to the closure of the semilunar valve is the phase of atrial relaxation to receive blood, ventricular contraction to push blood into the aorta.
    Note: This is the main work phase of the heart.
• Closure of the aortic valve occurs at the beginning of which cardiac cycle:
  • Isovolumetric relaxation: Closure of the aortic valve occurs at the beginning of the isovolumetric relaxation phase, when the pressure in the left ventricle falls below the pressure in the aorta.
    Note: Isovolumetric relaxation is the phase when the ventricle relaxes but the volume of blood in the ventricle does not change.
• The automaticity of the heart is manifested in:
  • The entire heart: The automaticity of the heart is manifested in the entire heart, meaning that the heart is capable of generating its own electrical impulses, ensuring the contraction of the heart.
    Note: The automaticity of the heart is due to the activity of the sinoatrial node, the atrioventricular node, and the His-Purkinje system.
• The fourth heart sound is caused by:
  • Ventricular filling: The fourth heart sound is caused by ventricular filling, when the atria contract, pushing blood into the ventricles.
    Note: The fourth heart sound is an abnormal heart sound, often heard in the elderly or those with heart disease.
• The heart receives blood from:
  • Coronary vessels and blood seeping from the heart chambers: The heart receives blood from the coronary vessels, providing oxygen and nutrients to the heart, and also receives blood seeping from the heart chambers, ensuring the heart has enough blood to pump out to the body.
    Note: The coronary vessels are a specialized blood vessel system that supplies blood to the heart.
• The conduction velocity in the ventricular muscle fibers:
  • 0.3-1 m/s: The conduction velocity in ventricular muscle fibers is 0.3-1 m/s, slower than the conduction velocity in the Purkinje system.
    Note: This difference in conduction velocity helps to ensure the synchronized contraction of the ventricles.
• The conduction velocity in the Purkinje system:
  • 1.5-4 m/s: The conduction velocity in the Purkinje system is 1.5-4 m/s, the fastest in the cardiac conduction system.
    Note: This rapid conduction helps to ensure the synchronized and efficient contraction of the ventricles.
• Phase 4 in the action potential is generated by which of the following factors:
  • Decrease in potassium outflow from the cell: Phase 4 in the cardiac muscle cell action potential is generated by a decrease in potassium outflow from the cell.
    Note: Phase 4 is the phase of membrane potential recovery, preparing for the next action potential cycle.
• The opening of L-type Ca2+ in the cardiac muscle cell membrane is in the phase:
  • Plateau: L-type Ca2+ opens in the plateau phase of the ventricular action potential, allowing Ca2+ from outside the cell to enter the cell, maintaining muscle contraction.
    Note: This is the main mechanism that helps the heart muscle to contract for a longer duration.
• Sympathetic stimulation leads to the secretion of which substance:
  • Only C and D are incorrect (dopamine and serotonin and acetylcholine): Sympathetic stimulation leads to the secretion of substances such as:
    • Norepinephrine (noradrenaline): Increases heart rate, increases heart contractility, vasoconstriction.
    • Epinephrine (adrenaline): Increases heart rate, increases heart contractility, vasoconstriction.

    Note: Dopamine and serotonin are other chemicals, not secreted when sympathetic stimulation is activated. Acetylcholine is secreted when parasympathetic stimulation is activated.

• The significance of Frank-Starling’s law:
  • Reflects the self-regulation of heart activity: Frank-Starling’s law shows the relationship between end-diastolic ventricular volume (preload) and heart contractility.
    Note: The larger the end-diastolic left ventricular volume, the stronger the heart contraction. This helps the heart to self-regulate its activity to pump out the appropriate amount of blood to meet the body’s needs.
• Which of the following is correct about arterial blood pressure:
  • Directly proportional to vascular resistance and cardiac output: Arterial blood pressure is directly proportional to vascular resistance and cardiac output.
    Note: Higher vascular resistance or higher cardiac output leads to higher arterial blood pressure.
• Which of the following is correct about mean arterial pressure:
  • The average of blood pressure measurements in the arteries to ensure blood flow: Mean arterial pressure is the average of blood pressure measurements in the arteries, helping to ensure stable blood flow.
    Note: Mean arterial pressure is usually calculated using the formula: (Systolic blood pressure + 2 x Diastolic blood pressure) / 3.
• Frank-Starling’s law:
  • Reflects the self-regulation of heart activity: Frank-Starling’s law reflects the self-regulation of heart activity, showing the relationship between preload and heart contractility.
    Note: The heart is able to self-regulate its activity to pump out the appropriate amount of blood to meet the body’s needs.
• What is the main mechanism of exchange across capillaries:
  • Passive diffusion: Passive diffusion is the main mechanism that helps to exchange substances across capillaries, from blood to cells and vice versa.
    Note: Substances move from areas of high concentration to areas of low concentration, without requiring energy.
• Arterial blood pressure:
  • Directly proportional to vascular resistance and cardiac output: Arterial blood pressure is directly proportional to vascular resistance and cardiac output.
    Note: Higher vascular resistance or higher cardiac output leads to higher arterial blood pressure.
• Rubbing on the carotid sinus area in a patient with a very fast heart rate will slow down the heart rate