Insulin is often thought of as simply a medication that is given to diabetics. However, insulin is a
hormone that our body produces itself (unless you have Diabetes Mellitus Type 1).
A hormone is a
molecule, typically a protein, that is produced in one part of your body but works in another part of your body. Insulin is made in the pancreas in response to blood glucose levels, glucose in your blood as a result of the food that you ate.
So, after you eat food that contains glucose, the pancreas releases
insulin which then tells the cell to let the glucose in. An interesting thing about insulin is that it does this in every cell of the body. Most hormones only act on a specific tissue.
Insulin has different effects depending on the cell upon which its acting.
Along with facilitating glucose getting into a cell, it can do other things. When insulin binds to a muscle cell, the muscle cell will make proteins (among other things). When it binds to a liver cell, the liver will make fat (among other things). In all tissues, insulin regulates how the cell uses energy.