Which hormone controls blood sugar?

Insulin, though it works as half of a pair. Insulin lowers blood glucose by letting it into cells; glucagon, from the same clusters in the pancreas, raises it by telling the liver to release stored glucose. The system is a thermostat with two directions, and the range it holds is narrow - roughly four to seven millimoles per litre, which is about a teaspoon of sugar in the entire bloodstream.

Type 1 and type 2 diabetes are different failures of that system, which the shared name obscures badly. Type 1 is autoimmune: the cells that make insulin are destroyed, usually early in life, and the person needs insulin to live. Type 2 is a loss of sensitivity - insulin is present and the cells stop responding - and it develops over years. Treating them as one disease has produced a great deal of misplaced blame.

The discovery in 1922 turned type 1 from fatal in months into manageable. Banting, Best and their colleagues sold the patent to the University of Toronto for one dollar each because they thought it belonged to the world - a decision that reads differently now that list prices in the United States rose to the point that people were rationing doses. Insulin is also the reason we know proteins have a definite sequence: Frederick Sanger worked out insulin's, the first protein ever sequenced, and won the first of his two Nobel Prizes for it.