Blood Sugar Control: Insulin and Glucagon

After a meal, sugar floods into your blood all at once. Hours later, with nothing eaten since, your blood sugar barely moves. Two opposing hormones from the same gland are quietly doing the work of keeping it steady either way.

Blood sugar, more precisely called blood glucose, is the body's main quick access fuel. Too little, and cells throughout the body, especially in the brain, run short of energy. Too much, and blood itself becomes damaging to blood vessels and organs over time. Keeping it within a working range is the job of two opposing hormones, both released by the pancreas. Insulin: lowering blood sugar after a meal When you eat, carbohydrate in your food is broken down into glucose, which enters the blood, often causing blood sugar to rise noticeably. The pancreas detects this rise and releases insulin. Insulin's main job is to help cells throughout the body take glucose out of the blood and use it for energy. It also directs some of the glucose into storage for later. As glucose moves out of the blood and into cells, blood sugar falls back toward its normal working range. Glucagon: raising blood sugar between meals Between meals, blood sugar naturally tends to fall as cells continue using glucose. The pancreas responds by releasing a second hormone, glucagon, which works in the opposite direction to insulin. Glucagon signals the release of glucose from the body's stored reserves, mainly in the liver, back into the blood. This keeps blood sugar from dropping too low even during a stretch without food, such as overnight sleep. The same gland, two opposing signals Insulin and glucagon come from different types of cells within the same gland, the pancreas. They are normally released in a carefully balanced opposing rhythm: more insulin after eating, more glucagon between meals. This is the same basic principle behind many of the body's internal balancing acts. Two opposing signals adjust a single measurement in opposite directions, rather than one signal simply switching on and off. What happens when this balance is disrupted The pancreas may fail to produce enough insulin. Or the body's cells may stop responding normally to the insulin that is produced. Either way, glucose builds up in the blood rather than moving into cells, and blood sugar rises too high. This is the core disturbance behind diabetes, a condition covered in far more depth later in the curriculum. Understanding normal insulin and glucagon function here is what makes that later explanation of diabetes make sense. What a doctor checks A doctor assessing blood sugar control is checking how well this balancing system is working, both at a single moment and over time. A single blood glucose reading. This shows the blood sugar level at that specific moment, useful for detecting an acutely high or low reading. A test reflecting recent months. Because glucose in the blood gradually attaches to certain blood cells, a specific blood test can estimate average blood sugar over the preceding few months. This gives a longer term picture than a single reading alone. Symptoms of imbalance. Excessive thirst, frequent urination, and unexplained tiredness can each suggest blood sugar running persistently high, while shakiness, sweating, and confusion can suggest it has dropped too low. When this system is affected Persistently high blood sugar, if not identified and managed, can gradually damage blood vessels and nerves throughout the body over years. This is why blood sugar control is checked even before other symptoms appear. This is explored further in the lesson "Diabetes and Metabolic Disease: Why One Ongoing Disturbance Affects So Much".

Insulin lowers blood sugar after eating by moving it into cells, while glucagon raises blood sugar between meals by releasing stored reserves, and both hormones come from the pancreas.