CVS 2 The Heart As A Pump Flashcards
List the general properties of cardiac muscle that allow the heart to act as a pump?
Striations
Branching
Centrally positioned nuclei(1 or 2 per cell)
Intercalated discs
Adherens-type junctions
Gap junctions
T tubules in line with Z bands (not A-I band junction as in skeletal)
What is systole and how long does it last?
contraction of heart- 280ms
What is diastole?
relaxation of heart between contractions, typically about 700ms
How does excitation spread in systole?
SA node fires AP which spreads over atria causing atrial systole.
AP reaches AV node where delayed for about 120ms
From AV spreads down bundle of his in septum
Spreads from inner (endocardial) to outer (epicardial) surface
Ventricle contracts from apex up, forcing blood towards outflow valves
How does organisation of muscle in ventricular walls facilitate pumping?
Organised into figure of eight bands that squeeze ventricular chamber forcefully in most effective way for ejection. Apex contracts first and relaxes last to prevent backflow
What are the differences between right and left heart?
Left has thicker myocardium as it must generate force to get blood all round body. Right side has pacemaker SA node
What is the inflow valve to the left ventricle?
Mitral
What is the outflow valve from the left ventricle?
aortic
When do outflow valves close?
When ventricles begin to relax and intraventricular pressure falls below arterial pressure and there is brief backflow shutting the valves
When do atrioventricular valves open?
When ventricular pressure falls below the atrial pressure in diastole. Atrial pressure had been gradually rising in systole as atria continue to fill with blood
What is the ‘rapid filling phase’?
Phase in diastole when a/v valves open and ventricles are filling with blood. Lasts about 200-300ms and is where most of ventricle filling occurs
What happens after rapid filling phase?
Ventricles continue to fill more slowly until intraventricular pressure matches atrial pressure causing av valves to close, rising as ventricular walls stretch
Do the ventricles fill during atrial contraction?
No. A tiny bit of blood enters during atrial systole but this amount is about the same as flows back when the valve shuts. Therefore the heart can pump fine without atrial contraction
What is isovolumetric contraction?
Event occurring in early systole where both inflow and outflow valves shut and the ventricles contact without changing in volume, increasing the intraventricular pressure
What is the rapid ejection phase?
Phase immediately after outflow valves open when blood ejected rapidly into the arteries
