Pancreas

The pancreas is a classic example of a mixed (partial endocrine) gland: most of its tissue is exocrine, secreting digestive enzymes through ducts into the small intestine, while scattered clusters of hormone-producing cells — the Islets of Langerhans — make up its endocrine component. Within these islets, distinct cell types secrete different hormones, most importantly beta cells (insulin) and alpha cells (glucagon); together these two hormones keep blood glucose within a narrow, healthy range.

Insulin is a peptide hormone whose main effect is to lower blood glucose — it is rightly called the hypoglycemic hormone. It does this by increasing glucose uptake into body cells, especially muscle and fat cells, and by inhibiting the breakdown of glycogen into glucose and the conversion of amino acids or fats into glucose. Insulin has a very short half-life in the blood (about 6 minutes) and is cleared from circulation within 10–15 minutes, which is why diabetic patients need frequent dosing. Modern therapeutic insulin (e.g. Humulin) is manufactured using recombinant DNA technology and must be given by injection, never orally, because digestive enzymes would simply break it down before it could act. …