ABSTRACT
Secretory glands have classically been divided into two distinct types, exocrine and endocrine. Exocrine glands secrete their products via the gland’s duct system into the external environment, such as the lumen of the gastrointestinal tract. In contrast endocrine glands release their products internally, initially into the interstitial fluid and then into the blood stream. However, there have been reports of endocrine secretion from glands traditionally thought to be purely exocrine organs (reviewed in Isenman et al., 1999).
