The endocrine system consists of many glands which secrete hormones in response to various stimuli. These hormones help cells communicate with one another. The endocrine system is responsible for almost every cell, organ and function in your body. The hormones released by the endocrine system play major roles in weight gain, sleep cycles, energy levels, even milestones such as puberty, menses and pregnancy. Diseases occur when the system is damaged by external factors or genetic abnormalities.