Islets of Langerhans

These are arranged in bundles in the endocrine region of the pancreas. They consist of alpha and beta cells. The alpha cells release glucagon which results in an increase in blood glucose concentration. Glucagon causes the liver to convert glycogen into glucose by hydrolysis. The beta cells secrete the hormone molecule insulin which has the opposite effect of glucagon by decreasing blood glucose concentration.  Insulin binds to membrane-bound receptors on target cells, allowing facilitated diffusion of glucose into the cells. It also activates the enzyme glycogen synthetase which converts glucose into glycogen for storage .