Little Organ, Big Job
The inside story of the pancreas
A tadpole-shaped gland, roughly the size of a medium banana, is nestled in the crook between your stomach and small intestine. Meet your pancreas. You've probably heard that the pancreas makes insulin, but this complex organ is more than just a one-hormone operation.
Science breaks down the jobs of the pancreas into two basic functions: digestive and hormonal. The pancreas produces enzymes for digesting food and hormones for regulating how the body uses food for energy. These hormones are chemical messengers that have important roles in eating, blood glucose, and, you guessed it, diabetes.
The Hormonal Pancreas
In the late 1860s, a German scientist named Paul Langerhans injected fragments of rabbit pancreas with a special dye and took a look at them under his microscope. He found that clusters of cells within the pancreas had taken up stain differently than the rest of the tissue. These clusters, which would later become known as the "islets of Langerhans," seemed to make up only about 1 to 2 percent of the organ's overall bulk, but they would prove to be vital, orchestrating the pancreas's hormone-secreting functions. It turns out that insulin, as well as several other hormones, are generated in the islets (pronounced EYE-lets) and then released into the bloodstream. Special receptors on the surface of healthy pancreatic islet cells are constantly monitoring blood glucose levels. When those levels are too high, beta cells in the islets release insulin. If the glucose levels are too low, glucagon—another pancreatic hormone—is released from a different set of cells within the islets. Glucagon promotes glucose production by the liver, helping the body avoid low blood glucose (hypoglycemia).
The Digestive Pancreas
Most of the pancreas concerns itself with the digestive system. It expels juices into the digestive tract that contain crucial enzymes necessary for getting nutrients out of food and into your body. Among the pancreas's cells is an elaborate network of ducts for the collection and transport of the digestive juices. The ducts feed directly into the upper part of the small intestine called the duodenum. The digestive enzymes complete the stomach's unfinished business, releasing all the nutrients from food so they can be absorbed in the small intestine. The pancreas's second important digestive task is neutralizing stomach acids that could tear up the sensitive lining of the small intestine. It squirts a neutralizing substance called bicarbonate into the duodenum, allowing partially digested food to continue safely on its journey.
The Pancreas in Diabetes
You are probably somewhat familiar with the pancreas's infamous connection to diabetes. Type 1 diabetes is an autoimmune disease caused when the immune system ruthlessly targets and destroys the pancreatic beta cells, leaving a person without an insulin supply. Because the insulin-producing capacity of the beta cells is completely lost in type 1 diabetes, all patients with type 1 require insulin for survival. In type 2 diabetes, the pancreas still produces insulin; it is the body that no longer heeds insulin's call to reduce blood glucose levels to normal, a situation known as insulin resistance. Eventually, the beta cells can't keep up with the body's extra demands for insulin, resulting in the onset of type 2 diabetes.
The causes of insulin resistance and beta cell failure in type 2 are not completely understood. However, insulin resistance can be overcome using drugs that stimulate the pancreas to make more insulin, drugs that help break down insulin resistance, insulin injections, or some combination of these agents.
In the case of type 1, things are a bit more complicated. One possible strategy for reversing type 1 is replacing the damaged hormonal functions of the pancreas with a functional donor pancreas—or with just the pancreatic islets, rather than the whole organ. Pancreas transplants are often successful, but islet transplantation is still experimental. With any transplant, the body may reject the donor tissue, and people with transplants need to take powerful antirejection medications. This obstacle could be overcome if replacement cells or organs could be derived from someone's own stem cells (general cells with the potential to develop into specialized cells such as beta cells). But with either transplantation or future use of stem cells, the same issue would remain: protecting new insulin-producing cells from the fate of the original beta cells, victims of an immune system gone haywire.
Another possibility is the construction of an "artificial pancreas." The hardware in a sense already exists: the continuous glucose monitor and insulin pump. Of course, the person using them must still interpret glucose readings and tell the pump how to respond. The key to an artificial pancreas would be coming up with software that can do all the things the human pancreas does so well, like being able to respond to changes in blood glucose rapidly and deftly with the release of just the right amount of insulin—no more, no less.
Do you need to know everything about the pancreas to manage your diabetes? Not at all. But knowing a little bit about this small but important organ can at least give you a greater appreciation for what your pancreas struggles with—and a greater understanding of diabetes.