Endocrine hormones are released by the thyroid, parathyroid, adrenal and other glands, guided by the pituitary gland. Hormones are involved in nearly all biological processes: immune function, reproduction, growth, and control of other hormones. Endocrine hormones signal molecules in a fashion similiar to the nervous system. Though while the nervous system communicates quickly, the endocrine system releases hormones to tell cells and tissues throughout the body how to behave over long periods of time.