How does the human body regulate its blood glucose levels?

Once a person has eaten a meal, their digestive system will break the nutrients down into smaller components that can travel in the blood to any parts of the body that need them. Any carbohydrates in this food will be broken down into sugars (e.g. glucose). These sugars will rapidly enter the blood. 

 At this point, it is critical for the body to use the glucose ASAP to avoid hyperglycaemia (high blood glucose) and maintain a constant blood glucose level. The glucose in the blood is therefore stored in liver and muscle cells in the form of a larger molecule called glycogen. 

 The body is able to detect blood glucose levels via an organ called the pancreas. More specifically, it is detected by areas within the pancreas called islets of Langerhans. In this region there are 2 types of cells. Beta-cells and alpha-cells.

 Beta-cells will detect high blood glucose (e.g. after a meal) and secrete insulin. Insulin is a hormone that will help the liver and muscle cell uptake more glucose and convert it to glycogen, thus lowering the overall blood glucose levels.

 Alpha-cells will detect low blood glucose (e.g. after exercise) and secrete glucagon. Glucagon is also a hormone, but it has the role of breaking down glycogen and releasing glucose from the liver and muscle cells. This will increase the blood glucose. 

 To provide an overview, the components within this system communicate with each other via hormones in order to provide a relatively constant blood glucose level. This maintanence of the internal environment is an example of homeostasis.