Phases of the cardiac cycle, pressures and volumes, heart sounds and murmurs, the ECG, the conduction system, Frank-Starling and the pressure-volume loop. 8 sections with a guided session, 87 flashcards, 66 quiz questions, 8 open questions and a practise test.
Subject: PHYSIOLOGY
The cardiac cycle is made up of two main phases: systole and what other phase? {0}
Answer: diastole
The cardiac cycle consists of systole (contraction) and diastole (relaxation).
At a resting heart rate of 75 beats per minute, what is the approximate total duration of one complete cardiac cycle?
Answer: 0.8 seconds
At a heart rate of 75 beats per minute, one cardiac cycle lasts about 0.8 seconds, with systole taking 0.3 seconds and diastole 0.5 seconds.
When heart rate increases, which component of the cardiac cycle experiences the most significant shortening?
Answer: Diastole
When heart rate rises, diastole shortens much more than systole. This reduces the time available for the ventricles to fill with blood.
When a person's heart rate increases significantly, what is the primary change in the duration of the cardiac cycle phases?
Answer: Diastole shortens much more than systole.
At higher heart rates, the heart needs to complete more cycles per minute. The body achieves this mainly by reducing the time spent in diastole, which is the heart's relaxation and filling phase. Systole, the contraction phase, shortens to a lesser extent.
When heart rate rises and diastole shortens, what specific process in the ventricles is primarily reduced? {0}
Answer: filling
Diastole is the phase when the ventricles relax and fill with blood. When diastole shortens significantly due to a high heart rate, the time available for the ventricles to fill is reduced.
What is the primary function of atrial systole in the cardiac cycle?
Answer: To provide a final push of blood into the ventricles before they contract.
Atrial systole is the phase where the atria contract to 'top up' the ventricles, adding a final volume of blood before ventricular contraction.
Which wave on an electrocardiogram (ECG) corresponds to atrial systole? {0}
Answer: P wave
The P wave on an ECG represents atrial depolarization, which immediately precedes atrial contraction (atrial systole).
During isovolumetric contraction, what is the state of the heart valves and the blood volume in the ventricles?
Answer: All four valves are closed, and ventricular volume remains constant.
Isovolumetric contraction is defined by the fact that all four heart valves (AV and semilunar) are closed. This allows ventricular pressure to build without any change in the blood volume inside the ventricles.
Which heart sound is produced by the closure of the AV valves at the beginning of isovolumetric contraction? {0}
Answer: S1
The first heart sound, S1, is caused by the closing of the mitral and tricuspid (AV) valves as ventricular pressure rises above atrial pressure at the start of isovolumetric contraction.
What condition must be met for the aortic valve to open and begin the rapid ejection phase?
Answer: Left ventricular pressure exceeds aortic pressure.
The rapid ejection phase begins when the pressure in the left ventricle becomes higher than the pressure in the aorta, causing the aortic valve to open and blood to be ejected.
During rapid ejection, the left ventricle must exceed approximately what pressure (in mmHg) to open the aortic valve? {0}
Answer: 80
The source states that left ventricular pressure passes aortic pressure, which is about 80 mmHg, to open the aortic valve during rapid ejection.
What is the primary characteristic of the reduced ejection phase of the cardiac cycle?
Answer: Blood ejection from the ventricles slows down as ventricular pressure falls.
In the reduced ejection phase, the ventricles are still ejecting blood, but the force of contraction is decreasing, causing ventricular pressure to fall and the rate of ejection to slow.
Which specific wave on an ECG corresponds to ventricular repolarisation during the reduced ejection phase? {0}
Answer: T wave
The T wave on the ECG represents the electrical repolarisation of the ventricles, which occurs during the reduced ejection phase.
During isovolumetric relaxation, what is the state of the heart valves and ventricular volume?
Answer: All four valves are closed, and ventricular volume remains constant.
Isovolumetric relaxation is defined by the fact that all four heart valves are closed, meaning no blood enters or leaves the ventricles, so their volume stays constant while pressure drops.
The closure of which valves marks the beginning of isovolumetric relaxation and produces the second heart sound (S2)? {0}
Answer: semilunar
The semilunar valves (aortic and pulmonary) close when ventricular pressure drops below arterial pressure, marking the start of isovolumetric relaxation and creating the S2 heart sound.
What event directly causes the atrioventricular (AV) valves to open, marking the beginning of the rapid filling phase?
Answer: Ventricular pressure falls below atrial pressure.
The rapid filling phase begins when the pressure inside the ventricles drops lower than the pressure in the atria. This pressure difference forces the AV valves open, allowing blood to flow quickly into the ventricles.
During which phase of the cardiac cycle does ventricular filling continue at a reduced rate, just before the atria contract?
Answer: Diastasis
Diastasis is the phase where ventricular filling slows down and continues at a reduced rate, occurring right before atrial systole.
Which statement accurately describes the pressure difference between the left and right ventricles and its anatomical consequence?
Answer: The left ventricle generates about five times the pressure of the right, resulting in a thicker left ventricular wall.
The left ventricle is responsible for pumping blood to the entire systemic circulation, which requires significantly higher pressure than pumping blood to the pulmonary circulation (the right ventricle's job). This higher workload and pressure lead to the left ventricle having a much thicker muscular wall.
Which cardiac pressure does pulmonary artery wedge pressure primarily help to estimate?
Answer: Left atrial pressure
Pulmonary artery wedge pressure is a clinical measurement specifically used to indirectly assess the pressure within the left atrium. This helps in understanding the filling pressures of the left side of the heart.
A patient's heart pumps 60 mL of blood with each beat. Before contraction, the ventricle held 120 mL of blood. What is this patient's ejection fraction?
Answer: 50 percent
Ejection fraction is calculated as stroke volume divided by end-diastolic volume. In this case, 60 mL (stroke volume) / 120 mL (end-diastolic volume) = 0.5, or 50 percent.
What is the term for the volume of blood remaining in the ventricle after systole? {0}
Answer: end-systolic volume
End-systolic volume (ESV) is the amount of blood left in the ventricle after it has contracted and ejected blood.
A person's heart beats 70 times per minute, and each beat pumps out 70 mL of blood. What is their cardiac output?
Answer: 4.9 L/min
Cardiac output is calculated by multiplying heart rate by stroke volume. In this case, 70 beats/min * 70 mL/beat = 4900 mL/min. Since 1000 mL equals 1 L, 4900 mL/min is 4.9 L/min.
Which measurement adjusts cardiac output for an individual's body size? {0}
Answer: cardiac index
Cardiac index provides a more standardized measure of cardiac performance by accounting for differences in body surface area among individuals.
Which event in the cardiac cycle directly causes the first heart sound (S1)?
Answer: The mitral and tricuspid valves closing
The first heart sound (S1) is produced by the closure of the atrioventricular (AV) valves, specifically the mitral and tricuspid valves, at the very beginning of ventricular contraction (systole). This prevents blood from flowing back into the atria as the ventricles start to pump.
At which specific location on the chest is the first heart sound (S1) typically heard loudest? {0}
Answer: apex
The first heart sound (S1) is loudest at the apex of the heart, which is usually located in the fifth intercostal space at the midclavicular line.
What event in the cardiac cycle directly causes the second heart sound (S2)?
Answer: Closure of the aortic and pulmonary valves
The second heart sound (S2) is produced by the closing of the semilunar valves (aortic and pulmonary) at the end of ventricular systole, as ventricular pressure falls below arterial pressure.
Why does physiological splitting of the second heart sound (S2) occur during inspiration?
Answer: Increased venous return to the right heart delays pulmonary valve closure
During inspiration, increased negative intrathoracic pressure enhances venous return to the right side of the heart. This increases right ventricular filling and stroke volume, causing the right ventricle to take slightly longer to eject its blood. As a result, the pulmonary valve (P2) closes a fraction of a second after the aortic valve (A2), creating the physiological splitting of S2.
During which phase of the cardiac cycle can the third heart sound (S3) be heard?
Answer: Rapid filling
The third heart sound (S3) occurs during the rapid filling phase of the cardiac cycle, when blood rushes into the ventricles.
In an adult over 40, what does the presence of a third heart sound (S3) typically suggest?
Answer: Volume overload, possibly indicating heart failure
While S3 can be normal in children, athletes, and pregnant individuals, in an adult over 40, it usually indicates volume overload, which is often seen in conditions like heart failure.
What is the primary reason the fourth heart sound (S4) occurs?
Answer: The atrium pushing blood into a ventricle that resists stretching.
The S4 heart sound is generated when the atria contract and push blood into a ventricle that is stiff or non-compliant, meaning it does not relax easily to accept the blood. This resistance creates the audible sound.
In which of the following conditions would you typically *not* expect to hear a fourth heart sound (S4)?
Answer: Atrial fibrillation.
S4 is caused by organized atrial contraction pushing blood into a stiff ventricle. In atrial fibrillation, the atria do not contract in an organized manner, so this specific mechanism for S4 cannot occur.
A doctor hears a heart murmur that is loudest at the right upper sternal border and radiates to the carotid arteries. The murmur is described as a crescendo-decrescendo sound occurring during systole. Which condition does this most strongly suggest?
Answer: Aortic stenosis murmur
The description of a crescendo-decrescendo systolic ejection murmur, loudest at the right upper sternal border and radiating to the carotids, is characteristic of aortic stenosis.
Aortic stenosis is known to have a specific effect on the difference between systolic and diastolic blood pressure. What does aortic stenosis do to the pulse pressure? {0}
Answer: narrows
Aortic stenosis causes the pulse pressure to narrow, meaning the difference between systolic and diastolic blood pressure becomes smaller.
A doctor listens to a patient's heart and hears a murmur that continues throughout systole, is loudest at the bottom tip of the heart, and can be heard extending towards the armpit. Which type of murmur is this most likely to be?
Answer: Mitral regurgitation murmur
Mitral regurgitation is characterized by a holosystolic murmur, meaning it lasts throughout systole, and is typically heard loudest at the apex with radiation to the axilla. The description matches these key features.
A patient presents with an 'opening snap' heard right after S2, followed by a low-pitched 'diastolic rumble' at the apex. Which heart condition does this sound pattern most likely indicate?
Answer: Mitral stenosis
The characteristic 'opening snap' after S2 and a 'low diastolic rumble' at the apex are specific signs of mitral stenosis, where the mitral valve is narrowed.
During which phase of the cardiac cycle does the murmur of mitral stenosis primarily occur?
Answer: After S2 (diastole)
The mitral stenosis murmur is described as an 'opening snap after S2' followed by a 'low diastolic rumble'. Both of these sounds occur during diastole, which is the period after S2.
A patient's heart murmur is described as an early diastolic decrescendo sound, heard best at the left sternal border. Which condition does this description most strongly suggest?
Answer: Aortic regurgitation
Aortic regurgitation is characterized by an early diastolic decrescendo murmur, meaning it occurs early in diastole and decreases in intensity. It is typically heard at the left sternal border.
Aortic regurgitation is associated with a specific change in blood pressure, where the difference between systolic and diastolic pressure increases. What is the term for this increased difference? {0}
Answer: pulse pressure
A wide pulse pressure, which is the difference between systolic and diastolic blood pressure, is a characteristic finding in aortic regurgitation.
What electrical event in the heart does the P wave represent? {0}
Answer: depolarisation
The P wave on an ECG signifies the electrical activation of the atria, known as atrial depolarisation, which precedes their contraction.
Atrial repolarization, the electrical event where the atria reset, is not visible as a distinct wave on a standard ECG. Where is this electrical activity typically hidden?
Answer: Within the QRS complex
Atrial repolarization occurs at the same time as ventricular depolarisation, which is a much larger electrical event. Because of its greater magnitude, the QRS complex masks the smaller atrial repolarization wave.
Which of the following best describes the PR interval on an ECG?
Answer: The delay of the electrical impulse at the AV node.
The PR interval primarily reflects the time the electrical impulse is delayed in the AV node, allowing the atria to finish contracting before the ventricles begin.
What is the specific condition indicated by a PR interval that is consistently longer than 200 milliseconds? {0}
Answer: heart block
A PR interval exceeding 200 milliseconds indicates first-degree heart block, meaning there is a prolonged delay in conduction through the AV node.
What electrical event in the heart does the QRS complex primarily represent? {0}
Answer: depolarization
The QRS complex specifically reflects the electrical depolarization of the ventricles, which precedes their contraction.
A patient's ECG shows a QRS complex that consistently measures 150 milliseconds. What does this finding most directly suggest about their cardiac function?
Answer: Slow ventricular conduction
A QRS complex that is wider than the normal 120 milliseconds indicates that the electrical impulse is taking longer than usual to spread through the ventricles, suggesting slow ventricular conduction.
A patient's ECG shows ST segment elevation. What does this finding most strongly suggest?
Answer: A transmural infarction
The ST segment represents the plateau phase when ventricular cells are fully depolarized. ST elevation is a critical indicator of a transmural infarction, a severe type of heart attack.
Which event in the cardiac cycle does the T wave on an ECG represent?
Answer: Ventricular repolarisation
The T wave specifically indicates the repolarisation of the ventricles, which is when they reset electrically after contracting.
A prolonged QT interval on an ECG can predispose a patient to what specific dangerous heart rhythm? {0}
Answer: torsades de pointes
A long QT interval indicates a delay in ventricular repolarisation, which can create an unstable electrical environment in the heart, leading to torsades de pointes.
Which of the following correctly describes the timing relationship between an ECG wave and a mechanical event in the cardiac cycle?
Answer: The QRS complex immediately precedes the first heart sound (S1).
The QRS complex represents ventricular depolarization, which triggers ventricular contraction. This contraction leads to the closure of the AV valves, producing the S1 heart sound, making the QRS complex occur just before S1.
What is the primary role of the sinoatrial (SA) node in the heart's electrical system?
Answer: To initiate the heart's electrical activity and set the normal heart rate.
The SA node is the heart's natural pacemaker. It generates the electrical impulses that start each heartbeat and sets the normal rate at which the heart contracts.
What is the primary function of the delay caused by the atrioventricular (AV) node in the cardiac conduction system?
Answer: To ensure the atria completely empty their blood into the ventricles.
The AV node's delay is essential for coordinating the heart's pumping action. It gives the atria time to finish contracting and push blood into the ventricles before the ventricles start their own contraction.
Which part of the cardiac conduction system is responsible for the slowest conduction speed? {0}
Answer: AV node
The AV node has the slowest conduction speed, which is crucial for creating the necessary delay between atrial and ventricular contraction.
What is the primary function of the bundle branches and Purkinje fibres in the heart's electrical conduction system?
Answer: To rapidly spread the electrical impulse throughout the ventricular muscle.
The bundle branches and Purkinje fibres are specialized for fast conduction, ensuring the electrical signal reaches all parts of the ventricles almost simultaneously for a coordinated contraction.
Which part of the cardiac conduction system has the fastest conduction speed? {0}
Answer: Purkinje fibres
The Purkinje fibres are noted for having the fastest conduction speed, about 4 m/s, which is crucial for the rapid and coordinated contraction of the ventricles.
Which component of the cardiac conduction system has the slowest conduction speed?
Answer: Atrioventricular (AV) node
The AV node is known for its slow conduction speed, which is crucial for delaying the impulse and allowing the atria to fully empty before ventricular contraction. The Purkinje fibres have the fastest conduction speed.
If the sinoatrial (SA) node fails to function, which part of the conduction system typically takes over as the pacemaker? {0}
Answer: AV node
The AV node serves as the primary backup pacemaker if the SA node fails, generating a heart rate of 40 to 60 beats per minute.
What is the main factor that determines the stretch of the ventricle at end-diastole, which is known as preload? {0}
Answer: venous return
Preload refers to the stretch of the ventricle at the end of diastole. This stretch is directly influenced by the amount of blood returning to the heart through the veins, which is called venous return.
According to the Frank-Starling law, what is the direct consequence of a larger end-diastolic volume in the ventricle?
Answer: A larger stroke volume with the next contraction.
The Frank-Starling law states that within physiological limits, a larger end-diastolic volume (meaning more stretch) leads to a more forceful contraction and thus a larger stroke volume. This mechanism helps the heart adapt its output to the amount of blood returning to it.
What is the term for the load or resistance the ventricle pumps against when ejecting blood? {0}
Answer: afterload
Afterload is the resistance the heart must overcome to pump blood out. It's essentially the pressure in the arteries that the ventricle pushes against.
What effect does an increase in afterload have on the heart's function?
Answer: It decreases stroke volume and increases end-systolic volume.
When afterload increases, the ventricle has to work harder against higher resistance. This means it ejects less blood, leading to a lower stroke volume, and more blood remains in the ventricle after contraction, increasing the end-systolic volume.
Which of the following would typically increase the heart's contractility?
Answer: Adrenaline
Adrenaline, along with sympathetic stimulation and noradrenaline, is known to increase the heart's contractility, making it pump with more force. Beta-blockers, acidosis, and calcium channel blockers all have the opposite effect, reducing contractility.
What is the effect of increased contractility on the heart's end-systolic volume (ESV) and stroke volume (SV)?
Answer: Decreased ESV and increased SV
When contractility increases, the heart muscle contracts with more force, ejecting more blood during systole. This means less blood is left in the ventricle at the end of systole (decreased ESV), and more blood is pumped out with each beat (increased SV).
How does an increase in afterload affect the pressure-volume loop?
Answer: It raises the top of the loop and moves the left edge to the right, making the loop narrower.
An increase in afterload means the ventricle has to pump against higher resistance. This causes the top of the loop to rise due to higher pressure, and the left edge (representing end-systolic volume) shifts to the right because the ventricle cannot eject as much blood, leading to a narrower loop overall.
A patient's blood pressure is measured at 135/85 mmHg. Based on this reading, what is their approximate mean arterial pressure (MAP)?
Answer: 102 mmHg
To calculate the mean arterial pressure (MAP), you first find the pulse pressure (systolic - diastolic). In this case, 135 - 85 = 50 mmHg. Then, you add one-third of the pulse pressure to the diastolic pressure: 85 + (1/3 * 50) = 85 + 16.67 = 101.67 mmHg, which is approximately 102 mmHg.
Which of the following conditions is associated with a widened pulse pressure?
Answer: Aortic regurgitation
Aortic regurgitation causes a widened pulse pressure because blood flows back into the left ventricle during diastole, leading to a lower diastolic pressure and a higher systolic pressure as the ventricle compensates by ejecting a larger volume.
Which event in the cardiac cycle causes the 'c' wave in the jugular venous pulse?
Answer: The tricuspid valve bulging into the atrium during ventricular contraction
The 'c' wave specifically reflects the tricuspid valve pushing back into the right atrium as the right ventricle begins to contract, increasing pressure in the atrium.
What is the name for the large, irregular jugular venous pulse waves that occur when the atria contract against a closed tricuspid valve, as seen in complete heart block? {0}
Answer: cannon
These distinct, large waves are known as 'cannon a waves' and are a specific sign of the atria contracting when the tricuspid valve is not open.
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