Heart Function Flashcards
Describe the properties of cardiac muscle and the events which occur after a SA node depolarisation
Cardiac muscle is an electrical syncytium whereby myocytes are connected via gap junctions allowing AP propagation.
Depolarisation leads to the opening of VOCC which triggers Ca-induced Ca release from the SR, Ca binds to binding pockets on troponin C causing a conformational change and exposing myosin head groups to bind and perform contraction
How long does a cardiac action potential last?
~280ms
Describe the muscle formation in the ventricles and how this is related to its function
The cardiac muscle is arranged in figure 8 corkscrews and allows blood to be “squeezed” up from the apex towards the outflow tracts
Name the valves of the heart in the order blood would first reach them if returning from the systemic circulation
Tricuspid valve
Pulmonary valve
Mitral valve
Aortic valve
Describe the features of the mitral and tricuspid valves which prevent inversion during systole
Valves attached to papillary muscles via chordate tendinae
What are the approximate durations of systole and diastole
Systole ~0.35s
Diastole ~0.55s
Name the 7 phases of the cardiac cycle
1 Atrial contraction 2 Isovolumetric contraction 3 Rapid ejection 4 Reduced ejection 5 Isovolumetric relaxation 6 Rapid filling 7 Reduced filling
For the 1 Atrial contraction phase of the cardiac cycle, state the following: Change in atrial pressure Function ECG changes State of each valve
Atrial pressure increases
Contributes to final 10% of ventricular filling
P wave
Mitral/tricuspid open aortic/pulmonary closed
At the end of Atrial contraction the ventricles are theoretically full, this is called the
End diastolic volume (~120ml)
For the 2 Isovolumetric contraction phase of the cardiac cycle, state the following: Change in atrial pressure Change in ventricular pressure ECG changes State of each valve Associated sounds
Atrial pressure increases with closing of valve Ventricular pressure increases QRS complex All valves closed S1 "lub"
For the 3 rapid ejection phase of the cardiac cycle, state the following: Change in atrial pressure Change in ventricular pressure Function State of each valve
Atrial pressure decreases as atrial base is pulled down
Ventricular pressure increases and begins to exceed aortic pressure
Opens the aortic valve and ejects blood from ventricle
Mitral/tricuspid closed aortic/pulmonary open
For the 4 reduced ejection phase of the cardiac cycle, state the following: Change in atrial pressure Change in ventricular pressure State of each valve ECG changes
Atrial pressure slowly increases with venous return
Ventricular pressure begins to decrease as muscle repolarises
Mitral/tricuspid closed aortic/pulmonary open
T wave
For the 5 Isovolumetric relaxation phase of the cardiac cycle, state the following: Change in aortic pressure Change in ventricular pressure State of each valve Associated sounds
Aortic pressure features dicrotic notch as valve closes
Ventricular pressure decreases to the point it is below aortic pressure causing the valve to close
All valves closed
S2 “dub”
For the 6 rapid filling phase of the cardiac cycle, state the following: Change in atrial pressure Change in ventricular pressure State of each valve Associated sounds
Atrial pressure decreases
Ventricular pressure decreases until below atrial pressure
Mitral/tricuspid open aortic/pulmonary closed
S3 present in normal children/adult pathology
For the 7 reduced filling phase of the cardiac cycle, state the following: Change in atrial pressure Change in ventricular pressure Function State of each valve
No change in atrial pressure
No change in ventricular pressure
Further ventricular filling driven by venous return
Mitral/tricuspid open aortic/pulmonary closed
