Session 2: Cardiac Cycle Flashcards
At rest, which part of the body does most of the cardiac output supply?
Gut
What are resistance vessels?
Arterioles that restrict blood flow to areas of the body that are hard to perfuse
What are capacitance vessels?
Veins - enable system to vary amount of blood pumped around the body
What is systole?
Period when the myocardium is contracting
What is diastole?
Period of relaxation between contractions (ventricles relax and fill with blood)
What is stroke volume?
What is the approximate value for this?
Volume of blood pumped by each ventricle per beat at rest ~70ml/beat
How much blood is pumped per minute at 70bpm?
What does this value correspond to?
5L/min ~ volume of blood in the body
What does the myocardium consist of?
Individual specialised muscle cells joined by low electrical resistance connections (gap junctions)
How is contraction of each cell produced?
Rise in intracellular Ca2+ concentration triggered by action potential (an all or none electrical event in the cell membrane)
What is the cardiac cycle?
Sequence of pressure flow changes and valve operation that occur with each heartbeat
Describe how excitation spreads throughout the different parts of the heart.
- action potential is generated spontaneously at the SA node (pacemaker cells) in the right atrium
- excitation spreads over the atria to the AV node
- it then moves down the muscular septum to excite the ventricular muscle from the endocardial side
- contraction then spreads through the ventricular myocardium and up towards the AV junction - valves located here
Complete the sentence: Heart valves open or close depending on _______________________.
Differential blood pressure on either side of the valve.
What do the cusps of mitral and tricuspid valves attach to?
Papillary muscles via chordae tendineae
What is the function of chordae tendineae?
Anchor the valve leaflets to prevent them from inverting on systole
Name the 7 phases of the cardiac cycle.
- Atrial contraction
- Isovolumetric contraction
- Rapid ejection
- Reduced ejection
- Isovolumetric relaxation
- Rapid filling
- Reduced filling
What does the A wave on the Wiggers Diagram denote?
Atrial pressure rising due to atrial systole
What role does atrial contraction play in ventricular filling?
It only accounts for final ~10% of ventricular filling (varies with age and exercise)
What is the state of all four valves in phase 1 of the cardiac cycle?
Mitral/Tricuspid: open
Aortic/Pulmonary: closed
What happens in phase 2 of the cardiac cycle?
ISOVOLUMETRIC CONTRACTION:
- all valves are closed
- blood volume doesn’t change
- intraventricular pressure > atrial pressure (mitral valve shuts)
- rapid rise in ventricular pressure as ventricle contracts
What does the C wave on Wiggers diagram denote?
Closing of mitral valve and slight inversion on atria causes this wave in atrial pressure curve
What is the S1 sound?
Closure of mitral and tricuspid valves (‘Lub’ sound)
