Cardiac cycle

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Cardiac cycle

Heart contracts - 75 bpm

systole - contract --- diastole - relax

in each cycle - deoxygenated blood enters RA via superior vena cavae

blood flows passively at first 

R contracts closing AV valve

rise in pressure forces pulmonary valve to open

simultaneously - oxygenated blood returns from lungs to LA via pulmonary veins

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Volume changes

end - diastole volume 100-120ml

during systole 60-70ml

end systole volume 40-50ml

cusp of AV valve come together

closure of aortic and pulmonary valves

Initiation and conduction of cardiac impulses - myogenic cardiac cells

generate APs and rhymatic contractions

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Cardiac muscle cells

contain Na, K, Ca channels 

Ca channels remain open for much longer - cell stimulated

Na channel open first - Ca channel open

Concentration gradient, K channels closed - repolarisation

Heart rhythms, coordinated essential

SA node cells have highest activity (pacemaker)

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Transmission of impulses

SA node --- atrial synctium

cells start to contract, rapid contraction

Atria contract simultaneously

intraventricular septum via AV bundle

AV bundle divides impulse passes through myocardium

SA node ---- myocardium

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Cardiac Arythiums

Irregular heartbeat

caused by different pacemaker

block in transmission from atria to ventricles



P wave

depolarisation of atria

occurs prior to atrial contraction

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QRS complex, T wave and Cardiac output

QRS complex - indicates  beginning of ventricular depolarisation

signals start of ventricular contraction

T wave - indicate repolarisation of ventricular muscle

Cardiac output - stroke vol X heart rate

- 65ml/beat X 75 bpm

- 4875ml/min

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