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 ...view middle of the document...
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 tissue that generates electrical activity this happens about 55-80 times per minute this piece of tissue is also known as the pacemaker.
The atrial contraction happens when a wave of excitation created by the SAN travels across the walls of both atria this excitation travels across the membrane of the tissue. As the wave pauses it causes the atria to contract this is called atrial systole.
At the base of the atrium there is a small disk of tissue that doesn’t conduct electricity so that the wave of excitation doesn’t cause the ventricles to contract at the same time as the atria.
At the top of the seprium separating the two ventricles there is another node called the atria ventricular node (AVN) this is the only way the wave of excitation can pass through the non-conductive tissue.
The wave pauses in the node so that the blood has time to drain from the atria into the ventricles before they contract.
After the pause the wave of excitation is carried down special conductive tissue away from the AVN.
This tissue os called the Purkyne tissue and it runs down the ventricular seprium.
At the bottom of the seprium the wave branches out over the walls of the ventricles as the wave moves across the base of the ventricle they contract this means that the ventricles contract from the bottom upwards.