Like other cell types (e.g., acinar pancreatic) dedicated to the synthesis of secretory proteins, peptide hormone–secreting endocrine cells are endowed with an abundant rough endoplasmic reticulum (ER), a stack of Golgi cisternae, and an array of dense-core secretory granules, all of which are components of an anterograde pathway for conveying secretory proteins to the extracellular space (Fig. 3-1). Classic morphologic and autoradiographic …