Please enable JavaScript.
Coggle requires JavaScript to display documents.
Heart (Cycles (Ventricular Filling First Stage (Transition (Atrial…
Heart
Cycles
Ventricular Filling
First Stage
Pressure in the heart is low at the beginning at this stage.
The atrioventricular valves are open as blood flows into the atria to their ventricles.
As the ventricles are filling the aortic and pulmonary valves are closed.
The ventricles are now 80 percent filled.
Transition
Atrial systole
Atrial systole is when the atria contract. As atria contract, blood is begin pressed into the ventricles
The blood being pressed against the ventricular wall causes a sudden increase in pressure.
Maximum volume is reached at the end of this stage, it is also called
end diastolic volume (EDV)
Consequently, the atria relax and the ventricles depolarize.
Isovolumetric Contraction
Second Stage
The ventricles begin to contract and causes ventricular pressure to rise rapidly and sharply
The rise in pressure causes the atrioventricular valves to snap shut.
The atrial are relaxed and will remain for the rest of this stage.
This brief instance is the only time that the ventricles are completely closed off temporarily. The pressure in the ventricles remains constant.
As the ventricle wall compresses the chamber, the pressure continues to rise which causes the semilunar valves to be forced open.
Ventricular Ejection
Third Stage
The blood is being moved out of the ventricles
Blood from the right ventricle is being moved into the pulmonary trunk.
Blood from the left ventricle is being moved into the aorta.
Isovolumetric Relaxation
Fourth Stage
The left over blood present in the ventricles is called
end systolic volume (ESV)
The pressure in both ventricles decreases drastically.
Both ventricles are now relaxed after they ejected the blood.
The semilunar valves shut to prevent back flow. This causes a slight rise of aortic pressure which begins the
dictrotic notch
This is another point where the ventricles are completely closed off.
The snapping shut of the semilunar valves causes the second “dub” sound.
The snapping shut of the atrioventricular valves causes the first “lub” sound.
As the atrioventricular valves are open and semilunar valves are closed, this causes the pause in the “lub” “dub” cycle.
Conduction
Sinoartrial (SA) Node
First Impulse
The SA node is located just below the entrance of the superior vena cava, which is in the right atrial wall
This region has the fastest depolarization rate than any other region.
Typically, the SA node sets the pace for the rest of the heart and is usually referred to as the hearts
pacemaker
The P wave in an ECG (electrocardiograph) comes from the movement of depolarization from the SA node.
Atrioventricular (AV) Node
Second Impulse
The AV node is located in the inferior part of the interatrial septum, right abound the tricuspid valve.
The impulse is delayed for 0.1 second to allow the atria to complete there response and contraction before the ventricles begin to contract.
The depolarization wave from the SA node reaches the AV node via the internodal pathway using gap junctions throughout the atria.
Atrioventricular (AV) Bundle
Third Impulse
Since the atria and ventricles are next to each other they aren’t connected by gap junctions. The AV bundle is the only electrical connection between the chambers since it is located in the superior part of the interventricular septum.
The impulse now passes from the AV node into the AV bundle, also called the
bundle of His
Bundle Branches
Fourth Impulse
The branches go along the interventricular septum to the apex of the heart.
As the impulse goes towards the apex, the QRS complex starts due to the ventricular depolarization.
The AV bundle then splits into two pathways, the left and right bundle branches.
Subendocardial Conducting Network (SCN)
Fifth Impulse
The bundle branches starts the excitement of the cells in the interventricular septum, but most of the ventricular depolarization is dependent on the SCN.
The impulse is usually by cell-to-cell transmission via gap junctions between ventricular muscle cells.
The SCN is also referred to as the
Purkinje fibers.
It completes the pathway of the bundle branches and penetrates into the heart apex and up the ventricular walls.
Since the left ventricle is larger, the SCN is more complex on the left side than the right side.
The SCN penetrates into the heart apex, and ventricular repolarization begins at the apex which causes the T wave in the ECG .
Regulation by the Autonomic Nervous System
Even though the intrinsic conduction system sets the basic rhythm of the heart rate, the autonomic nervous system modify the beat and introduce a subtle variance from one beat to the next.
The sympathetic nervous system is also known as the “accelerator.” It is responsible for the increase in the rate and force of the heart beat.
The parasympathetic nervous system is also known as the “brakes.” When it activates it is responsible for slowing the heart down.
The AV node is the slowest out of the other parts of the system to conduct impulses. Once past the AV node, the impulse passes the other systems rapidly.
As the P wave transitions into the QRS complex, the small impulse delay is at the AV node.