Pancreatic cell. Coloured transmission electron micrograph (TEM) of part of an acinar (exocrine) pancreatic cell. Mitochondria (red) are seen in the cell's endoplasmic reticulum (yellow) that surrounds the nucleus (blue). The endoplasmic reticulum regulates the secretion of many different types of inactive digestive enzymes called zymogens. The dark red blobs in the image are vesicles called zymogen granules, which transport the zymogen out of the cell. The zymogen enzymes are then activated in the small intestine during digestion. Magnification: x6000 when printed 10cm wide.