The blood system

About the heart

• The circulatory system transports substances around the body.
• The heart is an organ and pumps blood around the body. 
• Much of the wall of the heart is made from muscle tissue.
• There are four main chambers (left and right atria and ventricles) of the heart.

Sequence of blood in the heart

•  Blood enters the atria of the heart.
•  The atria contract and force blood into the ventricles.
• The ventricles contract and force blood out of the heart.
• Valves in the heart ensure that blood…