The pancreas is both an exocrine and endocrine gland. In the endocrine part, there are groups of cells called islets of Langerhans.
Four kinds of cells have been identified in the islets- alpha cells (glucagon), beta cells (insulin), delta cells (somatostatin), and PP cells (pancreatic polypeptide).
Insulin production:
In normal cases, insulin is produced and maintains the glucose level in the normal way.
In abnormal cases, the endocrine pancreas stops producing insulin. Insufficient insulin causes a disorder known as diabetes mellitus. But diabetes is two types- insulin-dependent or type 1 diabetes and insulin-independent or type 2 diabetes.
In both types of diabetes, the blood glucose level concentration is elevated above range due to deficiency of insulin.
Once this pancreatic disorder starts occurring, there is no further production of insulin from the pancreas.
In type 2, there may be the production of some insulin but the body cannot respond properly. In type 1 cases, no insulin is produced. So, the external application of insulin is the best way to meet up the deficiencies of insulin.