Pancreas cell. Coloured transmission electron micrograph (TEM) of an acinar (exocrine) pancreatic cell. Acinar cells secrete the inactive precursors (zymogens) of digestive enzymes to the small intestine, via the pancreatic ducts. The enzymes are secreted in vesicles known as zymogen granules (not seen) and are activated using proteolysis in the small intestine to aid the breakdown of carbohydrates, fats and proteins. The production and secretion of the zymogens are controlled by the cell's endoplasmic reticulum and golgi apparatus (blue/red). The cell's nucleus (purple, centre) and mitochondria (yellow) are visible.