Revision 2: Cardiac cycle and development of the CVS Flashcards
properties of cardiac muscle
striated
branched
1 or 2 centrally located nuclei
adherens-type junctions -> anchor cells and actin
intercalated discs -> elect. and mech. coupling w/ adjacent cells
gap junctions -> elect. coupling
The t tubules are in line with the Z line (in skel. muscle they are in line w/ the A-I junction)
systole and diastole
systole: period when myocardium is contracting, ~280ms
diastole: relaxation in between contractions, ~700ms
overall a heart beat therefore lasts about 1 second at rest
Organisation of cardiac muscle
figure of 8 bands -> squeeze ventricle chambers -> most effective for ejection of blood through outflow tract
apex contracts 1st and relaxes last to prevent back flow
Describe the cardiac cycle
1 atrial systole pumps a small amount of blood into the ventricles (it is not compulsory)
2 ventricular systole: a/v valves shut, slong with outflow valves -> ISOVOLUMETRIC CONTRACTION
3 outflow valves open as vent. pressure rises, blood is pumped into the aorta, rapid ejection phase
4 towards end of ventricular systole, intra-vent. pressure is still high but less is being pumped out
5 outflow valves shut, ventricles relax - ISOVOLUMETRIC RELAXATION
6 meanwhile, blood has been flowing into tha atria, pressure exceeds the ventricles, a/v valves open, rapid filling phase lasting 2-300ms
7 ventricles continue to fill until eventually vent=atrial pressure
heart sounds
1st (lub) - a/v valves shutting, oscillations produced in variety of structures
2nd (dup) - oscillations are produced in other structures including column of blood in arteries - shorter duration, higher freq, lower intensity
3rd sound can be heard in diastole and a 4th sometimes in atrial contraction
Murmurs: in ordinary individuals these can be produced by turbulent blood in exercise, at rest these may be due to narrowed valve or backflow from an incompetent valve
