Juvenile Diabetes Foundation

(Maharashtra Chapter)


Insulin is a hormone. And like many hormones, insulin is a protein. Insulin is secreted by groups of cells within the pancreas called islet cells. The pancreas is an organ that sits behind the stomach and has many functions in addition to insulin production. The pancreas also produces digestive enzymes and other hormones. Carbohydrates (or sugars) are absorbed from the intestines into the bloodstream after a meal. Insulin is then secreted by the pancreas in response to this detected increase in blood sugar. Most cells of the body have insulin receptors that bind the insulin that is in the circulation. When a cell has insulin attached to its surface, the cell activates other receptors designed to absorb glucose (sugar) from the bloodstream into the inside of the cell.

Without insulin, you can eat lots of food and actually be in a state of starvation since many of our cells cannot access the calories contained in the glucose very well without the action of insulin. This is why people with type 1 diabetes who do not make insulin can become very ill without insulin shots. Insulin is a necessary hormone. Those who develop a deficiency of insulin must have it replaced via shots or pumps (type 1 diabetes).

What is the role of pancreas?



Insulin Basics: How Insulin Helps Control Blood Glucose Levels

Insulin and glucagon are hormones secreted by islet cells within the pancreas. They are both secreted in response to blood sugar levels, but in opposite fashion!

Insulin is normally secreted by the beta cells (a type of islet cell) of the pancreas. The stimulus for insulin secretion is a HIGH blood glucose...it's as simple as that! Although there is always a low level of insulin secreted by the pancreas, the amount secreted into the blood increases as the blood glucose rises. Similarly, as blood glucose falls, the amount of insulin secreted by the pancreatic islets goes down. 

Glucagon is secreted by the alpha cells of the pancreatic islets in much the same manner as insulin... except in the opposite direction. If the blood glucose is high, then no glucagon is secreted. 

When blood glucose goes low, however, (such as between meals, and during exercise) more and more glucagon is secreted. Like insulin, glucagon has an effect on many cells of the body, but most notably the liver.

The Role of Glucagon in Blood Glucose Control

The effect of glucagon is to make the liver release the glucose it has stored in its cells into the bloodstream, with the net effect of increasing blood glucose. Glucagon also induces the liver (and some other cells such as muscle) to make glucose out of building blocks obtained from other nutrients found in the body (e.g., protein).

Our bodies desire blood glucose to be maintained between 70 mg/dl and 110 mg/dl (mg/dl means milligrams of glucose in 100 milliliters of blood). Below 70 is termed "hypoglycemia." Above 110 can be normal if you have eaten within 2 to 3 hours. That is why your doctor wants to measure your blood glucose while you are fasting...it should be between 70 and 110. Even after you have eaten, however, your glucose should be below 180. Above 180 is termed "hyperglycemia" (which translates to mean "too much glucose in the blood"). If your two blood sugar measurements are above 200 after drinking a sugar-water drink (glucose tolerance test), then you are diagnosed with diabetes.  

History of Insulin

The modern age has been full of amazing technological advances -- high-speed travel, the Internet, etc. However, if you have type 1 diabetes, you are no doubt a big fan of one particular 20th century innovation: insulin therapy. Before there was insulin therapy, people whose bodies stopped producing the hormone didn't hang around for long; there wasn't much doctors could do for them.

In the 19th century, after researchers figured out that the body needs this critical hormone to burn glucose as energy, doctors tried different ways to restart production of insulin in people with type 1 diabetes. Some physicians even tried feeding fresh pancreas to patients. The experiment failed (and probably left more than a few patients begging for a palate-cleansing sorbet), as did the other attempts to replace missing insulin.

Finally, in 1922, a former divinity student named Dr. Frederick Banting determined how to extract insulin from a dog's pancreas. Skeptical colleagues said the pancreas looked like "thick brown muck." Banting injected the insulin into the keister of a 14-year-old boy named Leonard Thompson, whose body was so ravaged by diabetes that he weighed only 65 pounds. Little Leonard developed abscesses on his bottom and still felt lousy, though his blood sugar improved slightly. Encouraged, Banting refined the formula for insulin and tried again six weeks later. This time Leonard's condition improved rapidly. His blood sugar dropped from 520 mg/dl to a more manageable 120 mg/dl. He gained weight, and his strength returned. (Poor Lenny -- although his diabetes remained in control for years, he died of pneumonia when he was just 27.)

Banting and a colleague, Dr. John Macleod, won the Nobel Prize for their work. Commercial production of insulin for treating diabetes began soon after. For many years, drug companies derived the hormone using pancreases that came primarily from stockyards, taken from slaughtered cows and pigs, which didn't need the organs anymore.

Animal insulin has saved millions of lives, but it has a problem: it causes allergic reactions in some users. In 1978, a fledgling biotechnology company named Genentech produced the first synthetically manufactured insulin that could be made in large amounts. Using bacteria or yeast as miniature "factories," the gene for human insulin was inserted into bacterial DNA. The result was human insulin, called recombinant DNA insulin, which did not cause the problems that animal insulin sometimes did.

When it became widely available in the early 1980s, this new insulin changed the treatment of diabetes forever. Today, almost all people with diabetes who require insulin use a form of recombinant human insulin rather than animal insulin.

Types of Insulin

Today all over the world, biosynthetic human insulin is made by recombinant DNA technology, a scientific process that allows for the production of nearly unlimited quantities of human insulin. Because insulin needs vary from person to person, different types of human insulin are available.

These include:

  1. Regular or R: A short acting insulin that begins to work within an hour but stops working sooner than intermediate or long-acting insulins. Peaks 2 to 4 hours and lasts 6 to 8 hours.

  2. NPH or N: An intermediate-acting insulin that peaks in 6 to 12 hours and lasts 18 to 26 hours.

  3. Lente or L: Another intermediate acting insulin.

  4. Ultralente: Long-acting insulin that begins to act in 6 to 8 hours, peaks in 14 to 24 hours, and lasts 28 to 36 hours.

  5. Humalog, lispro: Rapid-acting insulin is an analog of recombinant DNA technology in which two amino acids of the human insulin molecule -- proline and lysine -- have been reversed. It begins to work in 15 to 30 minutes, peaks 1 1/2 to 2 hours, and lasts 4 hours.

Current Insulin Delivery Systems

  1. Injections are the most common delivery system.

  2. Insulin pens look like a pen with a cartridge which holds 100 to 200 units of insulin.

  3. Insulin jet injectors look like a large pen. They send a fine spray of insulin through the skin at high pressure. These tend to be expensive.

  4. External insulin pumps are about the size of a pager. These are attached to the body through a narrow flexible tube with a needle just under the skin. A refillable cartridge holds insulin good for about 2 days. The needle and tubing need to be changed every other day and frequent glucose monitoring is necessary, but usually no more than if you take multi-injections a day to keep tight control.

  5. Internal insulin pumps are surgically implanted, usually in the abdomen. Users deliver insulin doses above and beyond the basal dose delivered by the pump during the day. The insulin goes directly to the liver as would normally occur in a person without diabetes.

  6. The insulin patch is placed on the skin and gives a continuous low dose of insulin during the day. To receive more insulin the user pulls off a tab on the patch.