Blood glucose concentration can also fall too low, for example between meals or during long exercise. The pancreas detects this and secretes the hormone glucagon into the blood.
Glucagon is carried in the blood to the liver. It makes liver cells convert stored glycogen into glucose, and the glucose is released into the blood. The blood glucose concentration rises back to normal and the pancreas stops secreting glucagon. This is negative feedback again.
Insulin and glucagon have opposite effects, and both are secreted by the pancreas. Insulin lowers blood glucose when it is too high, and glucagon raises it when it is too low. Working together, they keep the concentration within narrow limits. Adrenalin also makes the liver release glucose, which prepares the body for fight or flight.
