Insulin is a protein consisting of two amino acid chains joined by two disulfide cross-linkages. It is secreted by the beta cells of the Islets of Langerhans in the pancreas .

Effects of insulin:

In short, insulin brings down the blood glucose level.

A lack of endogenous insulin causes Insulin-Dependent Diabetes Mellitus (IDDM) whereas insulin resistance causes Non Insulin-Dependent Diabetes Mellitus (NIDDM)