The four major tissues in the structure of the human body mainly include epithelial tissue, muscle tissue, nerve tissue and connective tissue, with the functions of protection, movement, sensation and support respectively. 1. Epithelial tissue: mainly composed of epithelial cells, covering the surface of the body or organs; its main role is to protect the body and soft organs from external stimuli or damage. 2. Muscle tissue: mainly composed of muscle cells, through the diastole and contraction of muscle cells in order to complete the movement of the body and the normal peristalsis of the internal organs. 3. Nervous tissue: mainly composed of neurons and glial cells, its function is to sense and conduct external stimuli. 4. Connective tissue: composed of cells, interstitial cells and fibers, including blood, fat, bone and lymphatic tissues, etc. It mainly has the functions of nutrition, protection, support and defense.