The human body has nine major systems, including the motor system, digestive system, respiratory system, urinary system, reproductive system, circulatory system, endocrine system, nervous system and receptors. 1. Motor system: includes bones, joints and skeletal muscles, etc., which play the functions of movement, support and protection. 2. Digestive system: mainly consists of digestive tubes and digestive glands, which can digest and absorb the ingested food and expel the food residues out of the body. 3. Respiratory system: consists of lungs and respiratory tract, which can be divided into upper and lower respiratory tract. It is mainly involved in gas exchange. 4. Urinary system: including kidneys, ureters, bladder and urethra, which can discharge excess water and metabolic wastes from the body, out of the body. 5. Reproductive system: divided into external and internal genitalia, the main purpose is to reproduce offspring. 6. Circulatory system: including the cardiovascular system and the lymphatic system, which can transport nutrients and oxygen through the circulatory system to all parts of the body, and can make its metabolic waste transportation to the skin, kidneys and other parts of the body, and excreted. It can also transport heat and hormones for the body. 7. Endocrine system: including endocrine glands and endocrine tissues, which can participate in the regulation of the body’s internal environmental stability and human growth and development. 8. Nervous system: including central and peripheral nerves, which is the main regulatory system of the body. 9. Receptors: including endoreceptors, exoreceptors and proprioceptors, which can feel environmental stimuli. The major systems of the human body interact with each other to maintain normal body functions.