What is the role of the hormone insulin? How does it contribute to diabetes?

Insulin is a hormone released by the pancreas and it helps to control blood glucose levels. In a healthy person, when you have something to eat, the glucose is absorbed and enters your blood stream. In order for the body to break down this glucose and to produce energy, the glucose must enter cells. Insulin is needed in order to do this. It is therefore useful to think of insulin as the key to unlock the door to the cells allowing the glucose to enter and to be broken down to produce energy. 
In diabetes, one of two things can happen. In type one diabetes, there is no insulin, or key, to unlock the doors to the cells. This is as a result of the body’s immune system attacking the pancreas which is the organ that produces insulin.  In the case of type two diabetes, the insulin, or key, is present. However, it is unable to unlock the door properly. This is because there is a lack of insulin or the cells are unresponsive to insulin. The result is that glucose is trapped in the blood and it cannot enter cells to produce energy. This leads to several symptoms. The person will likely feel very tired. They may also feel very thirsty and frequently need to urinate. It is important that diabetes is treated as it can lead to several complications in the long run.