THE HUMAN BODYThe human body consists of nine main systems: the skeleton, the muscles, the nervous system, the hormonal system, the circulatory system, the digestive system, the respiratory system, the immune system, and the reproductive system.
Each system is made up of a number of organs. An organ is a part of the body with a specific purpose. Some organs, such as the liver or the skin, have more than one function.
Organs are made, from tissues. A tissue is a part of the organ made from similar cells and extracellular material.
Cells are the fundamental components of all organisms. They are composed of several different parts—the nucleus, the cytoplasm, the cell membrane, and various smaller parts— that have different functions.
