There are 10 major body systems, namely
The main role of the skeletal system is to provide support for the body, to protect delicate internal organs and to provide attachment sites for the organs.
The main role of the muscular system is to provide movement. Muscles work in pairs to move limbs and provide the organism with mobility. Muscles also control the movement of materials through some organs, such as the stomach and intestine, and the heart and circulatory system.
The main role of the circulatory system is to transport nutrients, gases (such as oxygen and CO2), hormones and wastes through the body.
The main role of the nervous system is to relay electrical signals through the body. The nervous system directs behaviour and movement and, along with the endocrine system, controls physiological processes such as digestion, circulation, etc.
The main role of the respiratory system is to provide gas exchange between the blood and the environment. Primarily, oxygen is absorbed from the atmosphere into the body and carbon dioxide is expelled from the body.
The main role of the digestive system is to breakdown and absorb nutrients that are necessary for growth and maintenance.
The main role of the excretory system is to filter out cellular wastes, toxins and excess water or nutrients from the circulatory system.
The main role of the endocrine system is to relay chemical messages through the body. In conjunction with the nervous system, these chemical messages help control physiological processes such as nutrient absorption, growth, etc.
The main role of the reproductive system is to manufacture cells that allow reproduction. In the male, sperm are created to inseminate egg cells produced in the female.
The main role of the immune system is to destroy and remove invading microbes and viruses from the body. The lymphatic system also removes fat and excess fluids from the blood.