The cardiac cycle Flashcards
The heart beats around…
70 times a minute.
The cardiac cycle the sequence of…
events which make up one heartbeat.
Atrial systole is a stage when…
the heart is filled with blood and the atrial walls contracts.
As the atrial walls contract…
blood flows from the atrium into ventricles.
The backflow in the atrium is prevented by…
closure of the valves in the veins.
The pressure in the atrium during contraction is not…
very great, as the walls are thin. But big enough to force the blood through atrioventricular valves.
Systole is…
contraction.
Diastole is…
relaxation.
Ventricular systole starts…
0.1 second after atrial systole and both ventricles contract.
During ventricular systole, the atrioventricular valves are…
pushed and shut by the pressurised blood in ventricles. The semilunar valves in the aorta and pulmonary artery are open.
The blood during ventricular systole flows from…
the ventricles into the arteries.
Ventricular diastole starts when…
muscle relaxes and the pressure in ventricles drops.
As the pressure drops in ventricular diastole drops…
the semilunar valves shut.
As the whole heart relaxes, blood flows…
into the two atria.
Cardiac muscle is…
myogenic, so it naturally contracts and relaxes(does not need impulses from a nerve).
Cardiac muscle contracts and relaxes…
rhythmically.
The heart has its own built-in…
controlling and coordinating system.
Sinoatrial node is…
pacemaker(SAN) so sets the rhythm for all the other cardiac muscles.
The natural rhythm of SAN is slightly…
faster than the rest of the heart muscle.
Each time the muscles of the SAN contract…
they set up a wave of electrical activity which spreads out rapidly over the whole of the atrial walls and both of them contract.
There is a band of fibres between the atria and…
ventricles, which does not conduct the excitation wave.
As the excitation wave spreads out from the SAN over the atrial walls, it…
cannot pass into the ventricle walls. The only way is through AVN.
Atrioventricular node is…
(AVN) a patch of conducting fibres in the septum.
The AVN picks up the excitation wave as…
it spreads across the atria, with a delay of around 0.1 seconds and passes the signal onto purkyne tissue.
Purkyne tissue is a bunch of…
conducting fibres, which run down the septum between the ventricles.
Purkyne tissue causes…
the muscle to contract from the bottom, squeezing the blood upwards.
Fibrillation happens when…
the excitation wave becomes chaotic passing through the ventricular muscle in all direction.
The fibrillation causes small…
sections of cardiac muscle contract while the others relax.
The fibrillation can be caused by…
electric shock or by damage to large areas of muscle in the walls. Almost always fatal.
ECG stands for…
electrocardiogram.
To obtain ECG, electrodes are…
placed on the skin over opposite sides of the heart and the electrical potentials generated are recorded with time.
The graph of ECG is…
voltage against time.
P on ECG represents…
the wave of excitation sweeping over the atrial walls.
Q, R and S on ECG represent…
the wave of excitation in the ventricle walls.
T on the ECG indicates…
the recovery of the ventricle walls.
