What is insulin?

Insulin is a hormone. It makes our body's cells absorb glucose from the blood. The glucose is stored in the liver and muscle as glycogen and stops the body from using fat as a source of energy. 

When there is very little insulin in the blood, or none at all, glucose is not taken up by most body cells. When this happens our body uses fat as a source of energy. Insulin is also a control signal to other body systems, such as amino acid uptake by body cells. Insulin is not identical in all animals - their levels of strength vary. 

Porcine insulin, insulin from a pig, is the most similar to human insulin. Humans can receive animal insulin. However, genetic engineering has allowed us to synthetically produce 'human' insulin.

The pancreas

The pancreas is part of the digestive system. It is located high up in your abdomen and lies across your body where the ribs meet at the bottom. It is shaped like a leaf and is about six inches long. The wide end is called the head while the narrower end is called the tail, the mid-part is called the body.

The pancreas has two principal functions:

1. It produces pancreatic digestive juices.

2. It produces insulin and other digestive hormones.

The endocrine pancreas is the part of the pancreas that produces insulin and other hormones.

The exocrine pancreas is the part of the pancreas that produces digestive juices.

Insulin is produced in the pancreas. When protein is ingested insulin is released.

Insulin is also released when glucose is present in the blood. After eating carbohydrates, blood glucose levels rise.

Insulin makes it possible for glucose to enter our body's cells - without glucose in our cells they would not be able to function. Without insulin the glucose cannot enter our cells.

Within the pancreas, the Islets of Langerhans contain Beta cells, which synthesize (make) the insulin. Approximately 1 to 3 million Islets of Langerhans make up the endocrine part of the pancreas (mainly the exocrine gland), representing just one fiftieth of the pancreas' total mass.

Discovery of insulin

In 1920, Dr. Frederick Banting wanted to make a pancreatic extract, which he hoped would have anti-diabetic qualities. In 1921, at the University of Toronto, Canada, along with medical student Charles Best, they managed to make the pancreatic extract.

Their method involved tying a string around the pancrease duct. When examined several weeks later, the pancreatic digestive cells had died and been absorbed by the immune system. The process left behind thousands of islets. They isolated the extracts from the islets and produced isletin. What they called isletin became known as insulin. 

Banting and Best managed to test this extract on dogs that had diabetes. They discovered insulin. In fact, they managed to keep a dog, that had had its pancreas taken out, alive throughout the whole summer by administering it the extract (which was, in fact, insulin). The extract regulated the dogs blood sugar levels.

At this point, Professor J. MacLeod, who had placed the laboratory at their disposal, said he wanted to see a re-run of the whole trial. After doing so he decided to get his whole research team to work on the production and purification of insulin.

J.B. Collip joined the scientific team, which now consisted of Banting, Best, Collip and MecLeod. They managed to produce enough insulin, in a pure enough form, to be able to test it on patients.

In 1922 the insulin was tested on Leonard Thompson, a 14-year-old diabetes patient who lay dying at the Toronto General Hospital. He was given an insulin injection. At first he suffered a severe allergic reaction and further injections were cancelled. The scientists worked hard on improving the extract and then a second dose of injections were administered on Thompson. The results were spectacular.

The scientists went to the other wards with diabetic children, most of them comatose and dying from diabetic keto-acidosis. They went from bed-to-bed and injected them with the new purified extract - insulin. This is known as one of medicines most dramatic moments. Before injecting the last comatose children, the first started to awaken from their comas. A joyous moment for family members and hospital staff!!

Collip did not get on too well with Banting and Best apparently - and he soon left the project. Best continued trying to improve the extract and managed eventually to produce enough for the hospital's demand. Their work was privately published. The Eli Lilly Company soon got to hear about it and offered to assist. It was not long before the Eli Lilly Company managed to produce large quantities of refined pure insulin.

In 1923 Banting and Macleod were awarded the Nobel Prize in Physiology or Medicine. Banting shared his prize with Best and Macleod shared his with Collip. The patent for insulin was sold to the University of Toronto for one dollar.