The pancreas contains clusters of cells that produce hormones. These clusters are known as islets. There are several different types of cells in an islet. For example, alpha cells make the hormone glucagon, which raises the glucose (a type of sugar) level in the blood. Beta cells make the hormone insulin, which lowers the glucose level. In type 1 diabetes, the body's immune system mistakenly destroys the beta cells. This causes the pancreas to lose the ability to make insulin.