Alpha cell

Alpha cells (α-cells) are endocrine cells in the pancreatic islets of the pancreas. They make up to 20% of the human islet cells synthesizing and secreting the peptide hormone glucagon, which elevates the glucose levels in the blood.
Function.
To elevate glucose levels, glucagon binds to receptors on hepatocytes (liver cells) and some other cells (e.g. kidney cells). This activates an enzyme, glycogen phosphorylase, inside the hepatocyte to hydrolyse glycogen into glucose. This process is called glycogenolysis.
In rodents, alpha cells are located in the periphery of the islets, however in humans, the islet architecture is generally less organized and alpha cells are frequently observed inside the islets as well. When viewed from an electron microscope, alpha cells can be identified by their characteristic granules with a large dense core and a small white halo.
Alpha cells also generate GLP-1 and may have protective and regenerative effect on beta cells. They possibly can transdifferentiate into beta cells to replace lost beta cells.