Endocrine refers to the hormones and the glands that produce and release them into the bloodstream, allowing them to influence organs far from their origin. These endocrine locations include the pituitary gland, pineal gland, thyroid, parathyroid glands, heart (which produces atrial natriuretic peptide), the stomach and intestines, the islets of Langerhans in the pancreas, the adrenal glands, kidneys (which produce renin, erythropoietin, and calcitriol), and adipose tissue (which produces leptin). Additionally, it involves the testes, the ovarian follicle (which releases estrogen), and the corpus luteum in the ovary. Endocrine functions are contrasted with exocrine activities. (Exocrine glands consist of the salivary glands, sweat glands, and glands within the gastrointestinal tract.)
