The Cardiac Cycle

Essay title: The cardiac cycle

The cycle starts with the filling process which is when both the atria and ventricles are both relaxed this is when the blood flows into the right atrium through the major veins.
The blood then flows through the atria ventricular valve and into the ventricles.
This part of the cycle is called Diastole.

The next part of the cycle is when both Atria contract this increases the pressure pushes the blood into the ventricles.
This part of the cycle is called atrial systole.

The final part of the cycle is when both ventricles contract this is called ventricular systole this raises the pressure in the ventricles very quickly.
This contraction starts at the bottom of the heart and pushes the blood upward toward the arteries.
The semi lunar valve then opens and the blood gets pushed out of the heart.
Finally the ventricles relax and the cycle starts again.

Inside the heart there are two types of valves they are called the atria ventricular valve and the semi lunar valve.

The atria ventricular valve at the start of the cardiac cycle allows the blood entering the heart to pass into the ventricles and it stops the blood flowing backwards from the ventricles into the atria.

The semi lunar valve stops the blood flowing back into the heart when it exits the heart via the aorta.

The lub sound that is heard when listening to the heart is the atria ventricular valves closing.
The dub sound that is heard when listening to the heart is the semi lunar valve closing.

Heart muscle (cardiac muscle) is unusual because it can cause its own contractions because of this it is called myogenic.
The heart muscle will contract and relax rhythmically even though it is not connected to the body.

The muscles from the atria and ventricles each have their own frequency of contraction the atrial frequency is higher than the ventricular frequency.

At the top of the right atrium is the sinoatrial node (SAN) this is a small piece of...