I will type using the Pancreas which is the largest gland in the human body. The collection of millions of cells in the Pancreas has Endocrine and Exocrine capability, the ability to produce hormones and release these hormones into the bloodstream are known as the islets of Langerhans, and there are four major types of cells that constitute the islets. of Langerhans they are the Alpha Cells, Beta Cells, Delta Cells, and Gamma Cells. Alpha Cells are those cells that produce and secrete a peptide hormone known as Glucagon and Glucagon is stimulated and released when. we have low glucose concentration inside our blood. We have Beta Cells that releases the hormone Insulin. Think of Insulin as the key that unlocks the cell for glucose to enter the cell where we derive our energy. I could go on and on but i thought i would start you off anyway. Good luck