7.5 The cardiac cycle Flashcards
Define cardiac cycle
Series of contractions ad relaxations that occur in the heart during one heart beat.
In what direction does blood flow?
From area of high pressure to area of low pressure
What causes high pressure and low pressure in the heart?
HP- Contractions
LP- Relaxation
What words are used to represent contractions and relaxation?
- systole
- diastole
What is the general order of the cardiac cycle?
Atrial systole to ventricular systole and lastly diastole
What happens in atrial systole?
The atria contracts which causes the pressure in the atria to become greater than the pressure of the ventricles. The atrioventricular valves (which are the valves between the atria and ventricles) will open and this causes blood from the atria to move into the ventricles.
What happens in ventricular systole?
The ventricles contract causing the pressure in the ventricles to become greater than the pressure of the atria.
As a result the atrioventricular valves close preventing back flow into the atria.
The pressure of the ventricles is also greater than the pressure of the arteries, causing the semi-lunar valves to open.
What happens during diastole?
The atria and ventricles are related meaning the pressure in the arteries is greater than the pressure of the ventricles.
As a result the semi-lunar valves close.
The pressure of the veins are greater than the pressure of the atria so now this draws blood into the heart via the veins.
As blood flows into the heart, this forces the atrioventricular valves to open and blood moves passively from the atria into the ventricles.
However the amount of blood entering the atria is still greater than the amount of blood leaving the ventricles passively, as a result the atria begin to fill up.
What sound does the cardiac cycle create and where does it come from?”
“Lub-Dub”
The 1st sound is cause by the atrioventricular valves closing during ventricular systole.
The 2nd sound is caused by the semilunar valves casing during diastole.
Pressure in the ventricles is so great and could cause the atrioventricular valves to fold inwards. What prevents this?
The heart has chords attached to the atrioventricular valves and to the walls of the ventricles, this holds it together preventing them from folding inwards.
Define cardiac output
what’s the equation for it?
the volume of blood pumped by one ventricle of the heart in 1 min.
Cardiac output= heart rate x stroke volume (vol of blood pumped out at each beat)
