If you have to get inside a locked house - What do you need? Keys to open the door. Similarly, there is a key which needs to be used for the glucose in the food you eat to get into the muscle cell, liver cells and all the other cells in the body. The key to all these cells is the Insulin released by the pancreas which is present in the blood cells. Once the key is turned in - the gates of the cells open allowing the entry of glucose, which is then utilized by the cells for the production of energy.