Pancreatic cells. Coloured transmission electron micrograph (TEM) of an acinar (exocrine) pancreatic cell (yellow) adjacent to an hormone- secreting (endocrine) Islet of Langerhans cell (pink). Acinar cells secrete zymogens (inactive digestive enzymes) in vesicles called zymogen granules (large bright orange blobs, left), which then become activated when in the small intestine. Islet of Langerhans cells regulate blood sugar levels by secreting hormones such as insulin and glucagon, that are also transported out of the cell by granules (small dark red dots, right). The large brown bodies (centre right and top right) are nuclei and the small brown organelles seen throughout are mitochondria.