the cardiac cycle Flashcards
what are the basic 3 events of the cardiac cycle
LV contraction
LV relaxation
LV filling
what is LV contraction
SYSTOLE & blood ejection
- wave of depolarisation occurs
- opens the L calcium tubule
- Ca2+ arrive at the contractile proteins
- LV pressure rises to more than LA pressure
- Mitral valve (MV) closes: this is M1 of the 1st heart sound
- isovolumic contraction of LV occurs - (increase in pressure but volume remain the same since valves remain closed) isovolumetric
contraction + relaxation is the only time when all valves of the heart are closed - Once the pressure in the ventricles exceeds that in the aorta & pulmonary trunk the aortic & pulmonary valves open 8. maximal ejection from ventricles into
the arteries occurs - ventricles DO NOT COMPLETELY EMPTY during contraction
how long does LV contraction take
0.3 seconds
what is LV relaxation
DIASTOLE & blood filling
- LV pressure peaks then decreases
- Reduced ejection
- Ventricles begin to relax and aortic and pulmonary valves close
- at this time the atrioventricular valves are closed thus no blood is entering or leaving the ventricles - ventricular volume is not changing known as isovolumetric ventricular relaxation (decrease in pressure but volume remains the same)
- Rapid left ventricle filling and ventricle suction - since blood in the atria is slightly
pressurised due to the venous return from the superior + inferior vena cava &
pulmonary vein, - pressure is enough to open mitral (or bicuspid left) and tricuspid valves (right), 7. also since there is a lower pressure in the ventricles blood just rushes in down the pressure gradient (effectively sucked in) - this is responsible for 80% of ventricular filling before atrial contraction
- Slow ventricular filling - since blood keeps flowing into atria from the veins,
pressure between the atrium and ventricle are equalising thus slowing filling this
pressure equalisation is known as DIASTASIS - where there is little to no net
movement of blood, at this point the AV node is delaying the stimuli from the SAN
to allow full ventricular filling - Atrial booster- pressure suddenly increases due to atrial contraction, enables ventricles to be actively filled - squeezing remaining blood from atria into ventricles
how long does LV relaxation take
0.5 seconds
how long is one cardiac cycle for a normal heart
0.8 seconds
what is physiologic systole
isovolumic contraction
maximal ejection
what is cardiologic systole
from M1 to A2
only part of isovolumic contraction - includes maximal and reduced ejection phases
what is physiologic diastole
reduces ejection
isovolumic relaxation
filling phases
what is cardiologic diastole
A2 to M1 interval (filling phases included)
define preload
the volume of blood in the left ventricle which stretches the cardiac
myocytes before left ventricular contraction
- how much blood is in the ventricles
before it pumps (end-diastolic volume).
When veins dilate it results in a decrease in preload (since by dilating veins the venous return decreases).
define afterload
the pressure the left ventricle must overcome to eject blood during
contraction - dilate arteries = decrease in afterload
what is starlings law of the heart
the larger the volume of the heart, the greater the energy of its contraction and the amount of chemical change at each contraction
Force of contraction is proportional to the end-diastolic length of
cardiac muscle fibre - the more ventricle fills the harder it contracts
effect of rest
At rest the cardiac muscle is not at optimal length. Below optimal length means the force of contraction is decreased - inefficient
* ↑ venous return = ↑ end diastolic volume = ↑ preload = ↑ sarcomere stretch =
↑ force of contraction thus = ↑ stroke volume and force of contractions
effect of standing
Standing decreases venous return due to gravity thus, cardiac output decreases,
which causes a drop in blood pressure, stimulating baroreceptors to increase
blood pressure
