When Kai was hungry and his blood glucose level was decreasing, glucagon is the hormone which was secreted by the islets of pancreas to increase the blood sugar levels in his body. Glucagon forces the liver to release the stored glucose in it, which increases the blood glucose level in the body. When Kai ate the sugar cookies there was enough of blood glucose available for his body, also it exceeded the requirement and went high. Insulin was then secreted to control this excess glucose from the islets of pancreas. As it helps the body cells to absorb the glucose and lowers the amount of glucose in the blood. It makes the cell available with the glucose to produce energy and perform their activities.
In short, glucagon and insulin both are secreted by the same organ which is islets of pancreas. But they differ in their function, glucagon increases the blood glucose when the body needs it, whereas insulin helps to absorb the excessive glucose and stores that in the body. Both are the hormones which help in regulating the body glucose levels Hope this helps its all i can do for you.