endocrine gland

Picture a factory that, instead of shipping its product out through a delivery chute to the loading dock, simply pours it straight into the river running past its back door. The river carries the product everywhere downstream. An endocrine gland works like that factory: it has no duct, and instead releases its hormones directly into the bloodstream.

An endocrine gland is a ductless gland that secretes hormones into the surrounding fluid and capillaries rather than through a tube to a surface or cavity. Because the blood is its delivery route, an endocrine gland is typically richly supplied with blood vessels. Examples include the thyroid, adrenal glands, pituitary, and the islets of Langerhans within the pancreas.

This stands in deliberate contrast to exocrine glands, which use ducts. Interestingly, some organs are both: the pancreas has exocrine tissue that pipes digestive enzymes into the gut and endocrine islets that drip insulin and glucagon into the blood. A caveat: ductless does not mean unstructured — endocrine glands are highly organized to package, store, and release hormones on cue.