Glucose is essential for the survival of all the cells in the body. It is the main energy source for all the metabolic activities in the body. Glucose reaches body tissues through blood circulation. It is essential to maintain adequate blood glucose level so that body tissues can utilize it appropriately. Blood glucose either above or below normal levels is dangerous. Various hormones regulate blood glucose levels. Most important among them is insulin. Insulin is secreted from beta cells of islets of Langerhan’s in a gland called pancreas. Insulin is essential to maintain blood glucose within normal limits. With the help of insulin body tissues utilize glucose. Insulin acts via insulin receptors present on different cells of the body. Insulin can be compared to a key and insulin receptor to a lock. When insulin attaches to its receptor on the cell, it results in opening of the gates for glucose. Glucose enters the cells, and is utilised by the cells. When glucose level in the blood increases, insulin is produced and it brings back the glucose to normal levels.