The Heart and Circulatory System
The regular heart beat and pulse is produced by contractions of the
heart muscle during the cardiac cycle. These contractions are caused
by an electrical stimulus called the cardiac impulse. This natural
pacemaker of the heart, called the Sinoatrial node, is located in the
Right Atrium.
The electrical impulse leaves the Sinoatrial node and travels to the
right and left Atria, causing them to contract together. After
contraction, there is a period of insensitivity to stimulation which
allows the Ventricles to fill with blood. The impulse now at the
Atrioventricular node moves to the Bundle of His then divides into the
Right and Left Bundle Branches where it spreads, using Purkinje
Fibers, to the muscles of the Right and Left Ventricle, causing them
to contract.
[IMAGE]
One-way flow of blood in heart and blood vessels
The heart is divided into 4 chambers:
1. Right Atrium
2. Right Ventricle
3. Left Atrium
4. Left Ventricle
The right side of the heart collects oxygen poor blood and pumps it to
the lungs
The left side of the heart collects oxygen rich blood from the lungs
and pumps to the rest of the body
[IMAGE]
Each chamber has a one way valve at its exit to prevent a backflow of
blood. When each chamber contracts blood is pushed through the valve
at its exit, which closes when contraction has finished.
Blood flow
Blood from body:
* → Superior and Inferior Vena Cava
* → Right Atrium
* → Tricuspid Valve
* → Right Ventricle
* → Semilunar Valve
* → Pulmonary Artery
* → Lungs
Blood from the lungs:
* → Pulmonary Veins
* → Left Atrium
* → Mitral valve
* → Left Ventricle
* → Aortic Valve