Insulin and Glucagon Regulate Blood Glucose

Your body keeps blood glucose in a narrow target range — roughly 70 to 100 mg/dL — around the clock, whether you just ate a bowl of pasta or slept through the night. That precision depends on two hormones made by the pancreas that act like a thermostat's heating and cooling systems: they push in opposite directions so the result stays stable. Inside the pancreas are tiny clusters of cells called the islets of Langerhans. Beta cells secrete insulin when blood glucose rises — after a meal, for example. Insulin signals liver cells, muscle fibers, and fat cells to take glucose out of the blood. In skeletal muscle and adipose (fat) tissue, insulin triggers the movement of glucose transporters called GLUT4 to the cell surface, allowing glucose to enter. In the liver, insulin works differently: it suppresses the liver's own glucose output by slowing glycogen breakdown and blocking new glucose production, while also promoting glycogen synthesis. Blood glucose falls back toward the set point, and insulin secretion tapers off. That tapering is the feedback — the falling glucose level removes the stimulus that triggered insulin in the first place. Alpha cells do the opposite. When blood glucose drops below the set point — during a long fast or intense exercise — alpha cells release glucagon. Glucagon targets the liver, triggering glycogenolysis (glycogen → glucose) and gluconeogenesis (making new glucose from amino acids or glycerol). Glucose pours back into the blood, the level rises, and glucagon secretion falls. Again, negative feedback. Think of insulin as the "store it" signal and glucagon as the "release it" signal. Neither hormone acts alone; their ratio at any moment tells target tissues which direction to go. A disruption — such as the immune destruction of beta cells in type 1 diabetes — removes insulin entirely, so glucose cannot enter muscle and fat cells, and the liver loses its brake on glucose output, causing blood levels to soar dangerously high. That single broken link shows just how critical this opposing-hormone balance is.