Fig. 15. The acinar unit. The columnar secretory cell has a basally located nucleus (arrow 1). Zymogenic secretory granules (arrow 2) are seen in the midportion and apical cytoplasm. A myoepithelial cell (arrow 3) is interspersed between the secretory cell and the basement membrane (arrow 4). (H & E, original magnification × 250; Courtesy of Ralph Eagle, MD, Philadelphia, PA)