cardiac cycle/heart sounds Flashcards
driving force in cvs
heart
distribution vessels in cvs
arteries
exchange vessels in cvs
capillaries
reservoir for blood in cvs
veins
why is a cvs needed
diffusion slow over x >1mm
what does the SAN create
pacemaker potentials
Phase 0 of A/V AP’s
RAPID DEPOLARISATION:
vg NA channels
Na influx
VGCCs start to open slowly
Phase 1 of A/V AP’s
EARLY REPOLARISATION
Na channels close
Phase 2 of A/V AP’s
PLATEAU PHASE
VGCCs fully open - Ca influx
K channel starts to open slowly
Phase 3 of A/V AP’s
RAPID REPOLARISATION
VGCC channels close
K channels open fully - K EFFLUX
Phase 4 of A/V AP’s
RESTING PHASE
Normal action of Na-K pump
Membrane impermeable to Na
Membrane permeable to K
Where is electrical activity first generated
SAN
What does contraction of myocardium generate
pressure changes within chambers
valves open and close depending on what
pressure changes in chambers
blood flow from venous return to pulmonary circulation
SVC, IVC RA tricuspid RV pulmonary semilunar valve pulmonary arteries lung circulation
blood flow from pulmonary to systemic circulation
lung circulation pulmonary veins LA mitral valve LV Aortic semilunar valve aorta Systemic circulation
step 1 electrical conduction
electrical activity generated at SAN spreads out via gap junctions
step 2 electrical conduction
At AVN, conduction is delayed to allow correct filling of ventricles.
step 3 electrical conduction
rapid conduction through bundle of His into ventricles
step 4 electrical conduction
conduction through purkinje fibres spreads throughout ventricles - ventricular contraction begins at apex
how long does systole last
0.34s
how long does diastole last
0.66s
cardiac cycle outline
- (v) diastole, atrial contraction
- ventricular isovolumetric contraction
- ventricular contraction and ejection / atrial filling
- ventricular isovolumetric relaxation
Δchambers, volume in ventricular diastole
blood: atria > ventricles; pressure in atria > ventricles; AV valves open - aided by atrial systole
Δchambers, volume in ventricular systole
pressure in full ventricles > atria; AV valves close; contraction increases pressure
Δchambers, volume, in ejection
pressure in ventricles > aorta & pulmonary artery valves open, ejection; blood enters atria
Δchambers, volume in ventricular diastole
pressure in pulmonary artery & aorta > ventricles;
aortic & pulmonary valves close
define end diastolic volume
volume of blood in ventricles at end of diastole when the mitral valve is closed
what is typical EDV
120ml
typical end systole volume
40ml
formula for ejection fraction
SV/EDV
(SV = EDV - ESV) =80ml
normal value for ejection fraction -
2/3rd or more - lower values in heart failure
a wave of atrial cycle
atrium contracting - tricuspid valvue open
x descent of atrial cycle -
atrium relaxing then filling, tricuspid closed
v wave of atrial cycle
atrium tense, full - tricuspid closed
y descent of atrial cycle
atrium emptying, tricuspid open
how is stroke work calculated
Δ in ventricular pressure * Δ in volume
what does the area inside the ventricular pressure-volume loop represent
the amount of stroke work done - relates to ENERGY CONSUMPTION during cardiac cycle
what causes heart sounds
vibrations caused by closure of cardiac valves; vibrations in ventricular chambers, turbulent flow of blood through veins
what is S1/Lubb
closure of AV valves at start of ventricular systole
what is S2/Dupp
closure of aortic/pulmonary valves at start of ventricular systole
what is S3
occasional - turbulent flow into ventricles, detected near end of first third of diastole
what is S4
pathological in adults - forceful atrial contraction against a stiff ventricle
