Release of granules into the lumina of ducts in the pancreas occurs via regulated secretion as a result of neural or humoral stimuli. Such stimuli emerge, for example, in case of food intake. Cellular mechanisms of granule release into the extracellular space (acinar lumen) may represent a kind of exocytosis when a granule-limiting membrane fuses with apical plasma membrane portion to produce a secretory pore. The membrane fusion of the granule and cell is guaranteed by fusion proteins (SNARE) and Ca²⁺.

The image depicts the lumen of a pancreatic acinus and apical zones of two acinar cells containing some secretory granules #1, #2, #3. One of the granules (on the right) is so close to the plasma membrane that it is difficult to distinguish their membranes. In the acinar lumen, one may see the contents of the granules (secretion) and microvilli of the apical surface #1, #2. The acinar lumen is separated from the intercellular spaces by tight (occluding) junctions #1, #2.