Session 2 - The heart as a pump Flashcards
What is the function of intercalated discs?
-Allow mechanical and electrical coupling so excitation can spread to all cells
Describe the characteristics of a cardiac muscle fibre
- Striated
- Branched
- Central nuclei (1 or 2 per cell)
- T-tubule in line with Z bands
- Intercalated discs
- Adherens and gap junctions
What is the function of gap junctions?
-All electrical coupling of cells to allow excitation to spread
What is the function of Adherens-type junctions?
-Anchor cells
How is ventricular muscle organised? Why is it organised this way?
- Into figure of 8 bands
- Arranged to allow forceful contraction of the ventricular muscle, contracting in a rotating way most effective for blood ejection
Which part of the ventricle contracts first/relaxes last?
-Apex
What are the pacemaker cells?
-Cells of the SA node which spontaneously depolarise, resulting in coordinated contraction of the heart
In what way is a cardiac action potential different to that of other cells?
-Very long
Describe the spread of excitation within the heart?
- SA node spontaneously depolarises
- Spreads over atria (atrial systole)
- AP reaches AVN
- Delay for approx. 120ms
- Excitation then spreads down the septum via the bundles of his and across the surface of the ventricles
- Excitation reaches the apex and then spreads up either side of the myocardium (depolarises from endocardium to epicardium)
Describe the pressure and volume changes of the left heart during the cardiac cycle (Start from early diastole)
- Early diastole -> Intraventricular pressure is less than atrial pressure, mitral valve opens and the rapid filling phase occurs
- Ventricles continue to fill at a steady state through diastole until intraventricular pressure is equal to atrial pressure
- Atrial systole occurs, forcing a little extra blood into the ventricles
- Intraventricular pressure is now greater than atrial pressure and regurgitation causes mitral valve to close
- Early systole-> isovolumetric contraction as both valves are closed causing intraventricular pressure to rise rapidly until it exceeds diastolic pressure of aorta
- Aortic valve opens and rapid ejection phase occurs, expelling the blood of the ventricles into the aorta, pressure in the ventricles and aorta rise to maximum
- As IVP falls below that of the aorta, the aortic valve closes and isovolumetric relaxation occurs, as both valves are closed, resulting in the ventricular pressure falling below atrial pressure and the cycle begins again
When do the outflow valves open?
-When pressure in the ventricles exceeds the pressure in the corresponding arteries (early systole)
When do the outflow valves close?
-When the pressure in the ventricles falls below that of the corresponding arteries (End of systole)
When do the atrioventricular valves open?
-When the pressure in the ventricles is less than the pressure in the atria (early diastole)
When do the atrioventricular valves close?
-When the pressure in the ventricles exceeds the pressure in the atria (early systole)
What is S1?
-The sound of the AV valves closing (lup)
