Pancreatic exocrine cells. Transmission electron micrograph (TEM) of a section through exocrine cells in the pancreas, showing numerous zymogen granules (circles), rough endoplasmic reticulum (ER, dark lines), and Golgi complexes (stacks of ER). These cells synthesize and secrete digestive enzymes into the small intestine. The enzymes are packaged into the zymogen granules in the cell's cytoplasm, where they are stored until needed. The cell clusters are called acini. Magnification x17000, when printed 10 centimetres wide.