It is called autocrine action. A hormone is a chemical substance produced in the body that controls and regulates the activity of certain cells or organs. Many hormones are secreted by special glands, such as thyroid hormone produced by the thyroid gland. They are essential for every activities of life, including the processes of digestion, metabolism among other activities. There are five types of signalling which include; intracrine, autocrine, juxtacrine, paracrine and endocrine cells.