Overview of the Pancreas and Islets and Their Role in Diabetes

The pancreas is a vital organ that produces chemical messengers called hormones. These hormones play a crucial role in controlling how our bodies use the energy we get from food (caloric intake), manage our energy needs, and regulate blood sugar levels (blood glucose). The pancreas is made up of different types of tissues, including tiny structures called islets of Langerhans. These islets are clusters of cells, containing five main types: beta-cells, alpha-cells, delta-cells, epsilon-cells, and pancreatic polypeptide cells. These cells communicate with each other to maintain a stable balance of glucose in the bloodstream.

However, when these cells experience stress or die, this communication network breaks down, leading to miscommunication and, consequently, elevated blood glucose levels. If blood glucose stays high over a long period, a condition called diabetes can develop.

Beta-cells have become a major focus for researchers because of their direct role in controlling blood glucose and their link to the development of diabetes. These cells release insulin, a hormone that lowers blood sugar by helping it move from the bloodstream into cells where it can be used for energy or stored for later. When glucose levels are high, this signals the beta-cells to release insulin. Insulin then removes glucose from the blood and stores it in other tissues as glycogen, which can be used later for energy. In Type 1 diabetes, the body’s own defense system (immune system) mistakenly attacks and destroys beta-cells, leading to a shortage of insulin. Type 2 diabetes occurs when the body doesn’t produce enough insulin to meet its needs, which are often higher than normal due to resistance to insulin’s actions.

Various factors can impair how well beta-cells function, including inflammation, an autoimmune attack, and prolonged periods of overactivity, all of which can result in insufficient levels of effective insulin and the development of diabetes.

Glucagon, another hormone produced by alpha-cells, has the opposite effect of insulin. When blood glucose levels drop too low, glucagon increases them by breaking down stored glycogen. In healthy individuals, high glucose levels prevent the release of glucagon. However, in people with diabetes, glucagon may continue to be released even when blood glucose levels are normal or high, further contributing to elevated blood glucose. The relationship between beta-cells and alpha-cells is particularly important because the opposing actions of insulin and glucagon are essential for maintaining normal blood glucose levels.

Somatostatin, a hormone made by delta-cells, can slow down or block the release of both insulin and glucagon. So far, using somatostatin to treat diabetes has not been successful because while it does suppress glucagon, long-term use also reduces insulin production, ultimately leading to increased fasting blood glucose levels.

Ghrelin and pancreatic polypeptide are hormones that control appetite and are released by epsilon and pancreatic polypeptide cells, respectively. Ghrelin signals hunger to the brain and increases appetite, while pancreatic polypeptide decreases appetite. Although their main role is in appetite control, these hormones also appear to protect beta-cells from damage and influence their function.

This complex network of cells is crucial for regulating and balancing blood glucose. When one type of cell releases too much or too little of its hormone, the entire system can become disrupted, leading to either a shutdown or uncontrolled activity. Therefore, if these cells don’t function correctly and communicate effectively, diabetes can occur. Maintaining proper communication between these cells is essential for keeping blood glucose levels stable.

This article was developed in partnership with Diabetes Action Canada as part of the Canadian National Graduate Course in Islet Biology and Diabetes hosted by the University Toronto (BCH2140).

About the author

Meagan Arbeau

Meagan is a PhD student in the Department of Physiology at the University of Toronto. Meagan is passionate about diabetes research and understanding its pathophysiology to aid in creating tools to improve the quality of life of those affected by the disease. Outside of the lab, Meagan enjoys health and wellness, fitness, and traveling.