Publisher Summary This chapter addresses the thyroid, parathyroid, and adrenal glands and the paraganglia; the pineal and pituitary glands. Endocrine organs are richly vascularized ductless organs that produce hormones. The epithelial cells of the organ secrete their hormone product directly into the bloodstream where, upon binding with specific receptors in target organs, cellular functions are affected. The endocrine system includes not only the endocrine glands (pineal, pituitary, thyroid, parathyroid, and adrenal glands) but also single cells and small clusters of cells in various organs such as the lung and gastrointestinal tract.