Insulin is absolutely required for all animal (including human) life. The mechanism is almost identical in nematode worms, fish, and mammals. In humans, insulin deprivation due to the removal or destruction of the pancreas leads to death in days or at most weeks. Insulin must be administered to patients in whom there is a lack of the hormone for this, or any other, reason.
Harvesting pancreases from human corpses is not practical on a large scale, so insulin from cows, pigs or fish pancreases is used instead. All have 'insulin activity' in humans as they are nearly identical to human insulin. Insulin is a protein which has been very strongly conserved across evolutionary time. Differences in suitability of beef, pork, or fish insulin preparations for particular patients have been primarily the result of preparation purity and of allergic reactions to assorted non-insulin substances remaining in those preparations.
Human insulin can now be manufactured, using genetic engineering molecular biology techniques, in sufficient quantity for widespread clinical use, much reducing impurity reaction problems. Eli Lilly marketed the first such synthetic insulin, Humulin, in 1982. Genentech developed the technique Lilly used.
The main job of insulin is to keep the amount of sugar in the bloodstream within a normal range. After eating a snack or a meal, sugar and other nutrients enter the bloodstream as the body digests food. Carbohydrates, protein and fats are three types of nutrients found in food. Although all three affect the amount of sugar in the bloodstream, carbohydrates affect it the most: During digestion, carbohydrates break down into sugar and enter the bloodstream in the form of glucose, a simple sugar.
Insulin also influences the liver, which plays a key role in maintaining normal blood-sugar levels. After eating, when insulin levels are high, the liver accepts and stores extra sugar in the form of glycogen. Between meals, when insulin levels are low, the liver releases glycogen into the bloodstream in the form of sugar, keeping blood sugar levels within a narrow and normal range.
When someone has diabetes, either because their pancreas secretes little or no insulin (type 1 diabetes), or their body has become resistant to insulin's action (type 2 diabetes), the level of sugar in the bloodstream builds up, which leads to diabetes complications if not treated.
Insulin therapy has two main goals:
Unlike many medicines, insulin cannot be taken orally. It is treated in the gastrointestinal tract precisely as any other protein; that is, reduced to its amino acid components, whereupon all 'insulin activity' is lost. There are research efforts underway to develop methods of protecting insulin from the digestive tract so that it can be taken orally, but none has yet reached clinical use. Instead insulin is usually taken as subcutaneous injections by single-use syringes with needles, or by repeated-use insulin pens with needles.
There have been several attempts to improve upon this mode of administering insulin as many people find injection awkward and painful. One alternative is jet injection (also sometimes used for some vaccinations) which has different insulin delivery peaks and durations as compared to needle injection of the same amount and type of insulin.
An insulin pump is a reasonable solution for some. However there are several major limitations – cost, the potential for hypoglycemic episodes, catheter problems and, at the time of writing, no approvable means of controlling insulin delivery in the field based on blood glucose levels. If too much insulin is delivered or the patient eats less than normal, there will be hypoglycemia. On the other hand, if too little insulin is delivered by the pump, there will be hyperglycemia. Both of these can lead to potentially life-threatening conditions. In addition, indwelling catheters pose the risk of infection and ulceration.
Tips on Taking Insulin: