C peptide

The pancreas is a fish-shaped endocrine gland that is tucked into the stomach and small intestine that has beta cells that secrete insulin; Insulin controls sugar (glucose) metabolism of the entire body. When the Insulin is produced within these cells, it lets off a byproduct, which is a protein molecule called 'c-peptide'. When Insulin is injected directly into body, there's no c peptide produced.