Cardiac cycle Flashcards
Convection
Mass movement of fluid caused by pressure difference
Describe the SA node
Group of cells located in the wall of the RIGHT ATRIUM
Can spontaneously produce action potential that travels through the heart
Sets rhythm of the heart - natural pacemaker
Rate of action potential production is influenced by nerves that supply it
Describe the AV node
Part of the electrical conduction system of the heart that coordinates the top of the heart
Electrically connects the right atrium and right ventricle - so atria have time to eject their blood into ventricles before ventricular contraction
What occurs during Phase 4 in SA pacemaker potentials
Membrane repolarises below the If threshold
At -50mV an Na+ channel opens = Na+ influx = slow depolarisation
What occurs during phase 0 in SA pacemaker potentials
Threshold is met for Ca2+ channels to open = Ca2+ influx = RAPID depolarisation
What occurs during phase 3 in SA pacemaker potentials
Ca2+ channels switched off
Activation of voltage gated K+ channels = K+efflux
What occurs during phase 0 of atrial & ventricular muscle action potentials
RAPID DEPOLARISATION
Recieve depolarisation stimulus from SA node = Na+ channels to open = Na+ influx
Ca2+ start to open slowly
What occurs during phase 1 of atrial & ventricular muscle action potentials
EARLY REPOLARISATION
Na+ channels close - cells begin to repolarise
What occurs during phase 2 of atrial & ventricular muscle action potentials
PLATEAU PHASE
Ca2+ channels open fully = Ca2+ influx = stops repolarisation
K+ channel open slowly
What occurs during phase 3 of atrial & ventricular muscle action potentials
RAPID REPOLARISATION
Ca2+ channels close
K+ channel open fully = K+ efflux
What occurs during phase 4 of atrial & ventricular muscle action potentals
RESTING PHASE
Na+/K+ pump
Systolic/ diastolic pressure in right atrium
1-5
Systolic/ diastolic pressure in right ventricle
25/5
Systolic/ diastolic pressure in left atrium
5
Systolic/ diastolic pressure in left ventricle
120/80
Systolic/ diastolic pressure in aorta
120/80
What does the area in a ventricular pressure volume loop show
Stroke volume
Relates to the amount of energy consumption during cardiac cycle
Equation for stroke volume
SV = EDV - ESV EDV = End diastolic volume ESV = End systole volume
Describe the steps of electrical conduction
1) Electrical activity generated in SA node spreads out via gap junctions into atria
2) At AV node, conduction is delayed to allow correct filling of ventricles
3) Conduction occurs rapidly through bundle of His into ventricles
4) Conduction through Purkinje fibres spreads quickly throughout the ventricles
