CVS 2.1 - The Heart as a Pump Flashcards
In which system of circulation is pressure high and in which is low? Why is this important?
- Systemic circulation = high
- Pulmonary circulation = low
- Output must be equal
What is systole?
Contraction and ejection of blood from the ventricles
What is diastole?
Relaxation and filling of the ventricles
Describe the structure of cardiac muscle. How is its structure related to its function?
- Distinct cells that are interconnected electrically
- Electrical signals can pass through freely so that beating can be synchronised
Describe the length of action potentials in cardiac muscle. What happens as a result of an action potential here?
- AP = long and lasts for one contraction
- AP spreads from cell to cell which contract in response causing an increase in intracellular Ca2+
What is the function of valves in the heart?
Allow blood to flow in one direction by opening or closing depending on different pressures
Which valves separate atria from ventricles?
- Tricuspid valve (right)
- Mitral valve (left)
Which valves lead to output vessels?
- Pulmonary valve
- Aortic valve
Describe the pumping system of the heart
Two pumps acting in series
What is the function of the valve cusps?
- Allow blood flow when pushed open
- Prevent back flow of blood when pushed closed
Where do the mitral and tricuspid valves attach? What is the function of this?
- Chordae tendinae
- Attach to papillary muscles which prevent the inversion of valves during systole
How long does the AVN delay the action potential signal for?
- ~120 ms
What are the stages of the cardiac cycle? (7)
1) Atrial Contraction
2) Isovolumetric Contraction
3) Rapid Ejection
4) Reduced Ejection
5) Isovolumetric Relaxation
6) Rapid Filling
7) Reduced Filling
Describe the events of atrial contraction
- Pressure increases in the atria due to contraction
- Mitral and tricuspid valves are open
- Aortic and pulmonary valves are closed
Which wave on the Wigger curve represents atrial contraction?
A wave
Which ECG wave represents atrial contraction?
P wave
What does atrial contraction result in? What does this mean?
- End diastolic volume (~120ml)
- Maximum amount of blood the ventricles can hold
Why does atrial contraction only provide the final 10-20% of blood to the ventricle?
- Ventricles are already 80-90% full from the previous cardiac cycle
- Ventricles passively fill with blood when the valves are open
Describe the events of isovolumetric contraction
- Ventricular contraction begins which increases pressure
- Intraventricular pressure becomes HIGHER than aortic pressure
- There is NO CHANGE in ventricular volume
Describe the positions of the valves during isovolumetric contraction
- Mitral and tricuspid valves = closed
- Pulmonary and Aortic valves = closed
Which wave on the Wigger curve represents isovolumetric contraction?
- C wave (closing of mitral valve)
Which ECG wave represents isovolumetric contraction?
QRS complex
Describe the events of rapid ejection
- Begins when intraventricular pressure becomes HIGHER than aortic pressure
- Rapid decrease in ventricular volumer as blood is pushed through to the aorta
- Decrease in atrial pressure causes atria to be pushed down which also decreases ventricular volume
- Blood is still flowing into atria from venous return
Describe the position of the valves during rapid ejection
- Mitral and tricuspid valves = closed
- Aortic and Pulmonary valves = open
Which wave on the Wigger curve represents rapid ejection?
- X descent
Describe the events of reduced ejection
- Repolarisation of ventricles = decreased tension
- Gradual increase in atrial pressure due to venous return
Describe the position of the valves during reduced ejection
- Mitral and Tricuspid = closed
- Aortic and Pulmonary = Open
Which wave on the Wigger curve represents reduced ejection?
V Wave
Which ECG wave represents reduced ejection?
T wave
Describe the events of isovolumetric relaxation
- Rapid decrease in ventricular pressure
- Ventricular volume remains constant due to closed valves
- Intraventricular pressure becomes LOWER than aortic pressure
- Brief back flow of blood from aorta
What does isovolumetric relaxation result in? What is this?
- End Systolic Volume
- The volume of blood left in the ventricles
Describe the position of the valves during isovolumetric relaxation
- Mitral and Tricuspid = Closed
- Pulmonary and Aortic = Closed
Define stroke volume. How is it calculated?
- Amount of blood ejected in each cycle, from each ventricle
- End Diastolic Volume - End Systolic Volume
Describe the events of rapid filling
- Intraventricular pressure is LOWER than atrial pressure
- Causes mitral valve to open which decreases atrial pressure
- Volume in ventricle increases
Describe the position of the valves during rapid filling
- Mitral and Tricuspid valves = Open
- Pulmonary and Aortic valves = Closed
Which curve on the Wigger graph represents rapid filling?
Y Curve
Describe the events of reduced filling
- Rate of ventricular filling slows (diastasis)
- Ventricle reaches relaxed volume
Describe the position of the valves during reduced filling
- Mitral and Tricuspid valves = Open
- Pulmonary and Aortic valves = Closed
During which stages of the cardiac cycle can the S1, S2 and S3 sounds be heard respectively?
- S1 = Isovolumetric Contraction (LUB sound)
- S2 = Isovolumetric Relaxation (DUB sound)
- S3 = Rapid Filling (Unusual. Common in children/pathology)
What happens to make the S1 sound?
Closure of the mitral valve
What happens to make the S2 sound?
Closure of the aortic valve
