Transmission electron micrograph of exocytosis taken from the rat pancreas. Images such as these indicated that secretory granules closely and selectively approach the apical membrane of the pancreatic acinar cell where exocytosis takes place, fuse with the apposed membrane, and release the content of secretory proteins into the acinar lumen without broaching the intracellular environment. The resulting omega figure is transitory, suggesting that the excess granule membrane is retrieved/recycled. Note the actin coat around the newly inserted granule membrane. Image made available by James D. Jamieson and the Department of Cell Biology, Yale University School of Medicine.