the cardiac cycle Flashcards
(9 cards)
what is the cardiac cycle?
this is the sequence of events during one heart beat
The diagram shows the changes on the left side of the heart.
what changes during the cardiac cycle?
volumes and pressures in the heart chambers change during the cycle and so does the pressure in the aorta
explain what is happening at each point in the diagram
0 - 0.1 seconds : the left atrium contracts and blood flows into the left ventricle
0.1 seconds : the left ventricle contracts, its volume decreases and the pressure inside increases above that in the atrium, closing the atrio ventricular valve
0.15 seconds : the pressure in the left ventricle increases above that in the aorta, opening the aortic valve (semilunar valve) and blood flows into the aorta
0.4 seconds : the left ventricle relaxes and the aortic valve closes as pressure in the aorta increases above that in the ventricle
0.45 seconds : the pressure inside the ventricle falls below that in the atrium. the atrium contracts, producing a small pressure above that in the ventricle. the atrio ventricular valve opens, allowing blood to flow into the ventricle.
0.8 seconds : one cardiac cycle is complete and the graph starts to repeat itself after this time
what is cardiac output?
cardiac output is the volume of blood pumped out of one ventricle per minute
how do you calculate cardiac output?
cardiac output = stroke volume (cm^3) x heart rate (min^-1)
what is stroke volume?
stroke volume is the volume of blood expelled from the left ventricle of the heart per contraction
what is heart rate?
heart rate is the number of contractions per minute
how do stroke volume and heart rate change during exercise?
during exercise the rate at which venous blood returns to the heart increases. the increased blood flow to the heart causes the cardiac muscle to contract more strongly, pumping out an increased volume of blood per beat, therefore stroke volume increases. the heart rate also increases during exercise.
what can regular exercise lead to?
regular exercise causes the heart to be stronger and the ventricles to be larger in size and volume. this leads to an increased stroke volume and a reduction in the resting heart rate.
