How are blood glucose levels controlled in the body?

Blood glucose is controlled by a negative feedback mechanism. 

When blood glucose levels rise, this is detected by beta cells in the Islets of Langerhans in the pancreas. In response, they secrete insulin which opens glucose channels in the membranes of cells (especially skeletal muscle and lievr cells) to allow glucose in so blood level decreases. It also casues rate of respiration to increase and the hepatocytes (liver cells) are stimulated to do glygogenesis. This is the storing of glucose as glycogen in order to reduce blood glucose level.

When blood glucose level falls to low this is detected by the alpha cells also in the Islets of Langerhans. In response they secrete glucagon into the blood which has an opposite effect to insulin. It decreases the cells permeability to glucose so it can remain in the blood. It also stimulates the hepatocytes to do glycogenolysis (the hydrolysis of glycogen to glucose) and gluconeogenesis (the production of glucose from fatty acids, glycerol and amino acids). These responses lead to an increase in blood glucose.