Insulin is a hormone secreted by beta cells of Islets of Langerhans of Pancreas. Its main function is to transport glucose from blood to the cells. In some individuals the gland is not able to secrete sufficient amounts of Insulin as a result of which the cellular uptake of glucose is affected. This is known as Insulin dependant Diabetes mellitus. In such individuals artificial Insulin is given so that the cells do not starve of glucose. This cannot be given orally as Insulin is proteinaceous in nature. Being a protein it is easily digestible in stomach due to enzyme Pepsin and in small intestine due to Trypsin and Dipeptidases. Thus insulin breaks before entering the bloodstream and this makes it ineffective.