alpha cell
If the beta cell is the brake that lowers blood sugar, the alpha cell is the accelerator that raises it. When glucose drops, for example between meals or during exercise, alpha cells release glucagon, the hormone that tells the liver to release stored sugar. They are the second most common islet cell after beta cells.
Alpha cells are exquisitely sensitive to low glucose, but their behavior is also shaped by their neighbors. Insulin and somatostatin released within the same islet directly suppress glucagon secretion, so glucagon output normally rises only when insulin falls. This local cross-talk means alpha and beta cells work as a push-pull pair rather than independently.
Alpha-cell dysregulation is increasingly recognized in diabetes. In type 2 diabetes glucagon is often inappropriately high, worsening fasting hyperglycemia, while in long-standing type 1 diabetes the glucagon response to hypoglycemia can fail, removing a key defense against dangerously low blood sugar.
The classical view that diabetes is purely an insulin problem has shifted to a bihormonal model: many endocrinologists now see diabetes as a disorder of the insulin-to-glucagon ratio, not insulin alone.