Question: What is insulin and why do some diabetics need to take it?
Answer: Insulin is a hormone. It's made by certain cells in the pancreas, which are called the beta cells of the pancreas, and the beta cells from the pancreas are part of these little islets called the Islets of Langerhans. That's where insulin normally comes from, and in type 2 diabetes there is always some insulin coming out from those beta cells; in type 1 diabetes, you tend to lose the beta cells and make no insulin.
Since 1921 or so, though, insulin has been available as a pharmacologic approach, so you can take insulin by injection, and you can replace what's not being made in the pancreas.
Who needs insulin? Well, it really is two situations. First of all, in type 1 diabetes, insulin is always necessary because the beta cells in the pancreas are not making any insulin. So, people with type 1 or juvenile onset diabetes always need insulin injections. In type 2 diabetes, you may also need insulin if your pancreas has sort of worn out to the point that it's not making anywhere near enough insulin, and you do need insulin injections. Type 2 diabetes often can be treated by different pills that might improve the insulin release by the pancreas or improve the response of the body to insulin, but eventually even type 2 diabetes may simply not be making, the pancreas may not be making enough insulin, and the person may need insulin by injection.
Next: What Causes Diabetes?