cardiovascular system

The Human Circulatory System

The Heart

The heart is an organ about the size of your fist that pumps blood through your body. It is made up of multiple layers of tissue. Your heart is in the center of your chest, near your lungs. It has four hollow chambers surrounded by muscle and other heart tissue. The chambers are separated by heart valves, which make sure that the blood keeps flowing in the right direction. 

The Human Circulatory System

The Human Circulatory System

Because the cells of a complex organism such as a human have many cells that are far from the outside environment where nutrients would come from. The system brings the materials to the cells that would not normally receive them.

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