Alpha cell

Alpha cells (more commonly alpha-cells or 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 to 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 being viewed by an electron microscope, alpha cells can be identified by their characteristic granules with a large dense core and a small white halo.

See also 

 Glucagonoma
 Beta cell

List of human cell types derived from the germ layers

References 

Category:Peptide hormone secreting cells