Endocrine system. Conceptual illustration of the endocrine system producing hormones. The blood circulation is represented as a ring surrounding three endocrine glands: the pancreas (pink) which secretes insulin and glucagon, the thyroid gland (yellow) which secretes thyroid hormones, and the adrenal gland (yellow, attached to the top of the kidney) which produces adrenaline and steroid hormones. Hormones are represented as coloured particles. Endocrine glands produce hormones which they secrete directly into the blood. Hormones are chemical signals which circulate around the body to target organs. They regulate physiology and behaviour.