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Questions and Answers
What is the primary role of heart valves?
What is the primary role of heart valves?
What is the function of chordae tendinae in the heart?
What is the function of chordae tendinae in the heart?
Which component is NOT part of the cardiovascular system's functions?
Which component is NOT part of the cardiovascular system's functions?
How does the heart respond to changes in metabolic demand?
How does the heart respond to changes in metabolic demand?
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What determines the opening and closing of heart valves?
What determines the opening and closing of heart valves?
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What initiates the P wave on the ECG during atrial systole?
What initiates the P wave on the ECG during atrial systole?
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During which phase of the cardiac cycle do all valves remain closed?
During which phase of the cardiac cycle do all valves remain closed?
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What occurs during the rapid ejection phase of the cardiac cycle?
What occurs during the rapid ejection phase of the cardiac cycle?
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What does the S2 heart sound correspond to in the cardiac cycle?
What does the S2 heart sound correspond to in the cardiac cycle?
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What change occurs during the isovolumetric relaxation phase in terms of pressure and volume?
What change occurs during the isovolumetric relaxation phase in terms of pressure and volume?
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Which of the following statements is true regarding LVEDP during atrial systole?
Which of the following statements is true regarding LVEDP during atrial systole?
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What happens to the atrial pressure during the reduced ejection phase?
What happens to the atrial pressure during the reduced ejection phase?
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What occurs immediately after the closure of the aortic valve?
What occurs immediately after the closure of the aortic valve?
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What effect does an increase in afterload have on the failing heart?
What effect does an increase in afterload have on the failing heart?
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Which factor primarily determines preload in the heart?
Which factor primarily determines preload in the heart?
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According to the Frank-Starling law, what happens to the heart's contraction force with increased preload?
According to the Frank-Starling law, what happens to the heart's contraction force with increased preload?
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Which of the following medications is commonly used in chronic heart failure to reduce workload?
Which of the following medications is commonly used in chronic heart failure to reduce workload?
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What component impacts afterload in the context of cardiovascular health?
What component impacts afterload in the context of cardiovascular health?
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What is the primary function of the sarcomere in cardiomyocytes?
What is the primary function of the sarcomere in cardiomyocytes?
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How does Ca2+ contribute to muscle contraction in cardiomyocytes?
How does Ca2+ contribute to muscle contraction in cardiomyocytes?
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What initiates the excitation-contraction coupling process in cardiomyocytes?
What initiates the excitation-contraction coupling process in cardiomyocytes?
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Which physiological changes result from stimulation of beta-adrenergic receptors in cardiac tissue?
Which physiological changes result from stimulation of beta-adrenergic receptors in cardiac tissue?
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What is the role of the troponin complex in muscle contraction?
What is the role of the troponin complex in muscle contraction?
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What is the consequence of removing Ca2+ from the cytosol after muscle contraction?
What is the consequence of removing Ca2+ from the cytosol after muscle contraction?
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How does the sodium-calcium exchanger contribute to cardiac muscle physiology?
How does the sodium-calcium exchanger contribute to cardiac muscle physiology?
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What effect does norepinephrine have on cardiomyocytes?
What effect does norepinephrine have on cardiomyocytes?
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What occurs during Phase 6 of the cardiac cycle?
What occurs during Phase 6 of the cardiac cycle?
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Which of the following best describes the event occurring during Phase 7 of the cardiac cycle?
Which of the following best describes the event occurring during Phase 7 of the cardiac cycle?
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How is stroke volume (SV) defined?
How is stroke volume (SV) defined?
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What does the Ejection Fraction (EF) signify?
What does the Ejection Fraction (EF) signify?
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What happens to the left ventricular pressure (LVP) during Phase 6?
What happens to the left ventricular pressure (LVP) during Phase 6?
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What is the relationship between cardiac output (CO) and heart rate (HR)?
What is the relationship between cardiac output (CO) and heart rate (HR)?
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What characterizes a sustained ventricular tachycardia?
What characterizes a sustained ventricular tachycardia?
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What does ST elevation in an ECG indicate?
What does ST elevation in an ECG indicate?
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What effect does increased preload have on myocyte function?
What effect does increased preload have on myocyte function?
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How does a premature contraction due to arrhythmia affect cardiac filling time?
How does a premature contraction due to arrhythmia affect cardiac filling time?
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Which of the following parameters describes systolic function?
Which of the following parameters describes systolic function?
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What is the primary role of the Frank-Starling mechanism in the heart?
What is the primary role of the Frank-Starling mechanism in the heart?
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Which branch of the nervous system plays a role in modifying cardiac function?
Which branch of the nervous system plays a role in modifying cardiac function?
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Study Notes
Cardiovascular System Control
- The cardiovascular system (CV) transports nutrients, oxygen, and waste products throughout the body.
- It also regulates body temperature (core to skin).
- The CV system buffers body pH and electrolytes.
- It transports hormones, such as adrenaline from the adrenal glands.
- The system assists in response to infection.
- It needs to rapidly respond to changes in metabolic demand.
Intended Learning Objectives
- Describe the sequence of the cardiac cycle.
- Describe how the heart initiates and conducts impulses.
- Identify the parts of the electrocardiogram (ECG).
- Describe the events causing heart muscle contraction.
Basic Cardiac Anatomy
- Aorta: Major artery carrying oxygenated blood away from the heart.
- Superior vena cava: Carries deoxygenated blood from the upper body to the heart.
- Pulmonary artery: Carries deoxygenated blood to the lungs.
- Pulmonary veins: Carry oxygenated blood from the lungs to the heart.
- Left atrium (LA): Receives oxygenated blood from the pulmonary veins.
- Right atrium (RA): Receives deoxygenated blood from the venae cavae.
- Left ventricle (LV): Pumps oxygenated blood to the body.
- Right ventricle (RV): Pumps deoxygenated blood to the lungs.
- Mitral valve: Separates the left atrium and left ventricle.
- Tricuspid valve: Separates the right atrium and right ventricle.
- Aortic valve: Separates the left ventricle and the aorta.
- Pulmonary valve: Separates the right ventricle and the pulmonary artery.
- Pressure readings are in mm Hg (systolic/diastolic)
Heart Valves
- Valves ensure unidirectional blood flow.
- Valve opening/closing is determined by pressure gradients (passive).
- Atrioventricular (AV) valves are between the atria and ventricles.
- Chordae tendinae and papillary muscles prevent AV valve backflow.
- Semilunar valves control blood into the exit arteries (aorta and pulmonary artery).
- Valve insufficiency (e.g., calcification or stenosis) causes blood regurgitation, potentially leading to heart failure.
Cardiac Function
- The heart's function is not further detailed.
The Cardiac Cycle
- The cardiac cycle involves systole (contraction) and diastole (relaxation) of the atria and ventricles.
- The Wiggers diagram plots pressure, volume, and ECG throughout the cardiac cycle.
- The diagram shows seven phases.
Phase 1: Atrial Systole
- The SA node initiates the P wave on the ECG.
- Active filling of ventricles occurs.
- Ventricles receive ~ 10-40% of their filling volume.
- LVEDP- LV end diastolic pressure
- S4 sound is during atrial contraction due to blood turbulence.
Phase 2: Isovolumetric Contraction
- QRS complex marks ventricular depolarization.
- Ventricular and papillary muscles contract.
- AV valves (mitral and tricuspid) close (S1 "lubb" sound).
- Ventricular pressure increases rapidly, but the volume remains constant.
- Ventricles become spherical in shape.
Phase 3: Rapid Ejection
- LVP > aortic pressure – aortic valve opens.
- Small pressure difference is seen.
- Max outflow velocity happens, so maximum blood ejected.
- Atria continue to fill during ejection, with atrial pressure dips.
Phase 4: Reduced Ejection
- T-wave repolarization marks the start of ventricular relaxation.
- Ventricular muscle relaxes.
- Ejection rate decreases.
- Atrial pressure increases due to continuous venous return.
Phase 5: Isovolumetric Relaxation
- LVP falls below aortic pressure – aortic valve closes.
- The short, sharp 'dupp' sound (S2) is heard.
- Blood flow momentarily stops due to elastic recoil.
- LVEDV – LV end diastolic volume.
- LVESV - LV end systolic volume
Phase 6: Rapid Filling
- LVP falls below atrial pressure, and AV valves open.
- Despite continued relaxation, filling occurs rapidly.
- Passive filling due to diastolic suction occurs.
- The S3 sound is if filling turbulence occurs.
Phase 7: Reduced Filling
- Passive filling is almost complete.
- Pressure gradient decreases, and filling slows.
- The ventricles become stiffer.
- The reduced filling phase occurs at rest, more prolonged.
Measuring Systolic Function
- Stroke Volume (SV): End diastolic volume (EDV)- End systolic volume(ESV)
- Cardiac output (CO): SV x heart rate (HR)
- Cardiac index: CO/body surface area
- Ejection fraction: SV/EDV x100
Electrical Conduction
- SAN initiates impulses, spreading over the atria.
- AVN slows conduction, creating a delay before ventricular contraction.
- Impulses spread through the ventricles via the bundle of his and purkinje fibres.
- Depolarisation occurs leading to muscle contraction.
SA Node Action Potential
- These cells spontaneously depolarize at a rate of ~1/s (automaticity).
- Sympathetic stimulation increases HR by increasing Ca2+ influx
- Parasympathetic stimulation decreases HR by increasing K+ permeability.
Action Potentials in Other Regions
- AVN action potential is similar to SAN, but with a different threshold.
- Purkinje action potential is relatively prolonged.
- Ventricular action potential also has a plateau phase.
Electrocardiogram (ECG)
- Detects changes in potential difference between electrodes on the heart surface.
- The body acts as a volume conductor.
- Used to diagnose arrhythmias, myocardial infarction, and other disorders.
Typical ECG
- P-wave: Atrial depolarization.
- QRS-complex: Ventricular depolarization.
- T-wave: Ventricular repolarization.
- P-R interval: Delay through the AV node.
- S-T interval: Plateau phase of the action potential.
Clinically Relevant ECG Results
- Sinus rhythm (normal healthy heart)
- Sinus bradycardia (slow heart rate)
- Atrial fibrillation (chaotic atrial rhythm)
- Ventricular fibrillation (chaotic ventricular rhythm).
- Bundle branch blocks and 2nd degree AV blocks
- Ventricular tachycardia
- ST-Elevation Myocardial Infarction (STEMI)
What Happens in Cardiac Muscle Cells
- Sliding filament theory describes muscle contraction.
- Excitation-contraction coupling involves Ca2+ and myofilament interactions.
- Myosin hydrolyzes ATP to form cross bridges.
Excitation-Contraction Coupling in Cardiomyocytes
- Action potentials trigger membrane depolarization.
- Ca2+ enters through L-type calcium channels.
- Calcium-induced calcium release (CICR) from SR.
- Cross-bridge cycling causes contraction.
- Ca2+ removal from cytoplasm causes relaxation
Regulation by Adrenoceptors
- Heart contains primarily β1 receptors.
- These receptors are activated by norepinephrine and epinephrine (adrenaline).
- Increased intracellular Ca2+ causes positive inotropy, chronotropy, dromotropy, and lusitropy.
- Agonists (e.g., dobutamine) support the heart, whilst antagonists (e.g., β-blockers) reduce workload.
Determinants of Ventricular Function
- Contractility (Inotropy)
- Preload
- Afterload
- Heart rate
- These factors affect stroke volume and cardiac output.
Afterload
- The load against which the heart works to eject blood.
- Determined by aortic pressure, aortic compliance, and peripheral resistance.
- High afterload increases workload.
Preload
- Myocyte stretch prior to contraction.
- Marked by end-diastolic volume or pressure (EDV/EDP).
- Higher sarcomere overlap increases force.
- Determined by venous return, and LV compliance and functionality.
Frank-Starling Law
- The heart contracts more forcefully when it is filled to a greater extent.
- Ventricular stretch increases force of ejection.
- Important in balancing both ventricular output.
- Failing hearts have impaired Frank-Starling responses.
Example of Frank-Starling Mechanism
- Myocyte stretch increases force generation.
- Higher venous return stretches myocytes, increasing ejection force.
- Critical for balancing ventricular output and contractility.
Summary
- The cardiac cycle phases are detailed using a Wiggers diagram.
- Systolic function parameters like cardiac output are vital.
- Autonomic nervous system and electrical conduction (SAN, AVN, Purkinje) are included.
- ECG abnormalities and typical waveforms are reviewed.
- Excitation-contraction coupling, and how it leads to heart muscle contraction is examined along with the roles of Ca2+.
- Regulation by adrenoceptors is considered.
- The effects and determinants of ventricular function, such as preload and afterload, are explained.
- The Frank-Starling law is crucial for understanding preload's effect on heart function.
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Description
Test your understanding of the cardiovascular system, including its functions, basic anatomy, and the cardiac cycle. This quiz will evaluate your knowledge of how the heart initiates impulses, conducts responses, and its role in maintaining homeostasis in the body.
