can insulin be orally administered to diabetic people or not? if not why?
Insulin is a protein hormone (pepetide hormone). If taken orally then it would be broken down into simpler component in the stomach i.e. into amino acid or peptones or dipeptides by the action of various proteolytic enzymes like rennin, pepsin, trypsin etc that will make it useless. The acidic condition of the stomach would denature it chemically. So it is injected directly into the blood.