= Endocrine gland
An <endocrine gland> releases <hormones> into the surrounding internal fluid for delivery to target <tissues>, commonly through the <blood>. Unlike an exocrine <gland>, it does not use a duct to discharge its hormonal <secretion> onto an epithelial surface or into an <anatomical lumen>.<Anatomy and Physiology 2e by J. Gordon Betts and others>[Section 17.1, Structures of the Endocrine System]{ref}
The <thyroid> and pituitary are examples. The <pancreas> shows why classification can be functional: its endocrine <cells> release <hormones> such as <insulin>, while other pancreatic <cells> send digestive <secretion> through ducts. <Hormone> delivery alone does not specify the response. A target <cell>'s <receptors> and intracellular signaling determine whether and how it reacts, and feedback can regulate further <secretion>.
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