How is insulin released in response to raised plasma glucose?

Raised plasma glucose concentration means greater entrance of glucose into beta cells in the Islet of Langerhans in the pancreas. This increased concentration glucose means greater metabolism of glucose, producing elevated levels of ATP intracellularly. This closes potassium channels in the plasma membrane of the beta cells, leading to a build up of intracellular potassium. This means a build up of intracellular positive charge, leading to depolarization of the cell membrane. This activates voltage gated calcium channels. These open leading to an influx of calcium. The resultant increase in intracellular calcium triggers exocytosis of vesicles within the cell, vesicles which contain insulin. Insuli is therefore released by exocytosis, from beta cells, into the blood stream.