Heart and Circulatory System
By Teacher C

The heart is a hollow cone shaped muscular pump, approximately 14 cm wide
It sits behind the sternum and rests on the diaphragm
It has four chambers with two atrium and two ventricles
The right atrium receives oxygen poor blood from two different veins, the superior vena cava (upper body blood) and inferior vena cava (lower body blood)
From the right atrium, the blood passes through the tricuspid valve
This tricuspid valve directs blood flow from the right atrium to the right ventricle, remaining open during ventricular filling 
When the ventricle contracts, the tricuspid valve closes to prevent back flow of blood into the right atrium
From the right ventricle, blood is pumped through the pulmonary valve, preventing back flow from the pulmonary artery into the right ventricle
Blood is pumped from the pulmonary artery to the lungs where it cleansed and receives oxygen
Blood returns to the hearts left side by four pulmonary veins, two from each lung
Blood enters into the left atrium, and then enters a double flapped mitral valve
It proceeds to the left ventricle
As the ventricle contracts, the mitral valve prevents a back flow of blood into the left atrium
Blood passes through the aortic valve into the aorta, which is the major artery that supplies blood to the entire body
Arteries carry blood with oxygen to the capillaries and deliver oxygen to body tissues
Veins carry back blood to the heart, after oxygen is delivered to cells, to reenter into the right atrium