The immune system is the system in your body that is responsible for protecting the body against invasion by diseases. It also protects from pathogens, it removes dead cells, and also removes abnormal cells. The parts of the immune system are very complex and important to the human development. The thymus forms part of the immune system. White blood cells protect are body. Anti bodies detect harmful substances. The epidermis is the skins protective outer layer. The cilia are important in the human and animal development. Mucus acts as a protective blanket over surfaces preventing the tissue underneath from drying out. Last the saliva releases a fluid that contains water, electrolytes, mucus, and enzymes, all of which flow out of the animus into collecting ducts.