Cardiac Cycle Flashcards
cardiomyocytes
heart muscle cells
intercalated discs
connect cardiomyocytes and allow coordinated contraction
what organelle are cardiomyocytes rich in
mitochondria - lots of ATP required for continuous contractions
right vs left ventricle
right - thinner myocardium , large lumen
left - thick myocardium, generates much greater BP to overcome aortic pressure
what are the two AV valves
between atria and ventricles
tricuspid (right)
bicuspid (left) also known as mitral
LAB RAT
when do the AV valves open
when pressure in the atria exceeds that of the ventricles, forced closed when ventricular pressure higher than atria
what are the two semi lunar valves called
right - pulmonary valve
left - aortic valve
between ventricles and artery
papillary muscles
projections of the ventricular walls that fasten AV valves to ventricular walls preventing there movement therefore preventing backflow of blood
chordinae tendineae
fibrous connective tissue (heart strings) that connect papillary muscles to the valve cusps
valve regurgitation
valves not closed tightly so blood leaks back into chambers
valve stenosis
stiffening of valve cusps so valves dont open fully therefore insuffcient blood flow
end diastolic volume
volume of blood in ventricle prior to contraction
end systolic volume
volume remaining in ventricle after contraction
how is stroke volume calculated
EDV - ESV
volume of blood ejected per heartbeat
how is HR determined
HR determined by rate at which sino-atrial node fires action potentials.
however the autonomic NS determines the rate of APs and therefore HR
chronotrophy
heart rate
where is the SA node located
wall of the right atrium
describe the path of the AP across the heart
1 - SA node fires
2 - excitation spreads through atrial myocardium initiating atrial contraction
3 - AV node fires
4 - impulse spreads down bundle of HIS which then splits into left and right bundle branches
5 - then spreads to purkinje fibres which distributes excitation through ventricular myocardium
describe how action potentials are generated at the SA node
1 - leaky Na channels allow slow Na influx (pacemaker potential)
2 - once threshold reached voltage gated Ca+ channels open allowing Ca into the cell
3 - at peak Ca channels close and K+ channels open allowing K+ to leave cell causing rapid hyperpolarisation
describe ventricular action potentials
1 - rapid depolarisation - via fast Na channels and slow Ca channels
2 - early repolarisation - at peak Na channels close and K+ channels open
3 - plateau phase - K+ efflux is balanced by Ca influx
4 - repolarisation - Ca channels close and K+ efflux dominates
what do ECGs detect
electrical activity of the heart
P wave
shows atrial depolarisation
QRS wave
shows ventricular depolarisation
T wave
shows ventricular repolarisation
