Insulin

Molecular structure of insulin. Source: CDC

Insulin is an essential hormone produced by the pancreas and involved in nutrient metabolism. An absolute deficiency of insulin results in type 1 diabetes, which is fatal if insulin is not replaced. A relative deficiency of insulin results in type 2 diabetes, for which insulin injections are one of several treatment options. The discovery, characterization, and commercialization of insulin are landmarks in the history of 20th-century medicine.

The body breaks food down into organic compounds, one of which is glucose. The cells of the body use glucose as a source of energy for movement, growth, repair, and other functions. Before the cells can use glucose, it must move from the bloodstream into individual cells. This process depends on insulin.

Types

Vials of Humalog and Lantus. Source:

The body produces insulin in one form. There are more than 20 types of commercially available insulin products. They exist in four basic forms, each with a different time of onset and duration of action. The more commonly used types of insulin follow:

• Rapid-acting. These are insulin analogs, such as aspart or lispro. This form of insulin begins to work within 5 to 15 minutes and is active for 3 to 4 hours.

• Short-acting. An example is regular insulin. It starts working within 30 minutes and is active for about 5 to 8 hours.

• Intermediate-acting. An example is NPH, or lente insulin. It starts working in one to three hours and is active for 16 to 24 hours.

• Long-acting. An example is ultralente insulin. It starts working in four to six hours and is active for 24 to 28 hours.

• Insulin glargine and insulin detemir. These are insulin analogs that start working within one to two hours and continue to be active, without major peaks or dips, for about 24 hours, although this varies in many individuals.

• A mixture of NPH and regular insulin. This compound starts working in 30 minutes and is active for 16 to 24 hours. There are several variations with different proportions of the mixed insulins.

The decision as to which insulin to choose is based on an individual's lifestyle, a physician's preference and experience, and the person's blood sugar levels. The criteria considered in choosing insulin include the following:

• Onset: How soon it starts working.
• Peak time: When it is at its peak concentration and works the most.
• Duration: How long it lasts in the body.

Description

Low- and high-power views of a pancreatic islet. The brown stain corresponds to insulin and identifies the cells as beta cells. Source: NIH

Insulin is used medically to treat some forms of diabetes mellitus. By reducing the concentration of glucose in the blood, insulin is thought to prevent or reduce the long-term complications of diabetes, including damage to the blood vessels, eyes, kidneys, and nerves.

Role of Insulin in the Body

Insulin helps turn food into energy for the body to work. Insulin is a naturally-occurring hormone secreted by the pancreas. It is required by the cells of the body in order for them to remove and use glucose from the blood. From glucose the cells produce the energy that they need to carry out their functions.

How It Works

When glucose enters the blood, the beta cells automatically produce the right amount of insulin, causing the body's cells to take up glucose from the blood, as well as liver, muscle, and fat tissue cells. Insulin also allows the body to store glucose as glycogen in the liver and muscles, and stops the breakdown of fat to energy. When insulin is absent or low, glucose is not taken up by most body cells, and the body begins to use fat instead as an energy source. Once inside the cells, glucose is broken down to provide energy. Insulin lowers the blood glucose whether food is eaten or not, so meals and snacks must be eaten on schedule if someone is using insulin to treat a medical condition.

Diseases Involving Insulin

An insulinoma is a rare tumor of the islet cells in the pancreas that results in excessive production of insulin. The diagnosis can be confirmed by measuring an inappropriately high concentration of insulin in the blood. Insulin deficiency diseases (diabetes), however, are far more prevalent.

Type 1 Diabetes

Type 1 diabetes is much less prevalent than type 2, and management of this form of diabetes always involves insulin injections, since patients with type 1 diabetes do not make enough of their own insulin to sustain life. Before insulin therapy, type 1 diabetics—almost all of them young—had a life expectancy of less than a year from diagnosis. The wasting away from lack of nourishment was characterized by unquenchable thirst and hunger. As the body attempted to use fats in place of carbohydrates, abnormally high concentrations of volatile "ketone bodies" built up, which gave the breath a characteristic sweet smell ("acetone halitosis") characteristic of end-stage disease.

Type 2 diabetes

Type 2 diabetes (also called non-insulin-dependent diabetes mellitus or adult-onset diabetes) is primarily characterized by insulin resistance, insulin deficiency, and hyperglycemia (high blood sugar). Though people can be diagnosed at a younger age, type 2 diabetes occurs most often in adults after the age of 40.

In patients with type 2 diabetes, the pancreas usually makes plenty of insulin, but it cannot be used correctly for the production of energy. This type of diabetes often runs in families. Being overweight and not getting enough exercise are also risk factors for this type of diabetes. Type 2 may be managed by engaging in exercise and modifying one's diet. However, after someone has had type 2 diabetes for a few years, their body may stop making enough insulin. If this is the case, diabetes pills or insulin may be needed.

Insulin Therapy

Various types of Insulin Therapies exist. Please see the "Insulin Therapy" article to learn more.

Related Professions

• An endocrinologist is a medical doctor trained in the care of problems in the endocrine, or hormonal, system.

• A gastroenterologist is a medical doctor who is trained to treat problems in the digestive system, including the pancreas.

• Diabetes educators are health care professionals trained to help individuals with diabetes make lifestyle changes that will lead to better health.

History

How insulin was discovered

Researchers first gave an active pancreatic extract containing insulin to a young diabetic patient in 1922. The FDA first approved insulin in 1939. Currently, insulin used for treatment is derived from beef and pork pancreas as well as recombinant (human) technology. The first recombinant human insulin was approved by the FDA in 1982.

The Nobel Prize in Medicine or Physiology in 1923 was awarded to Frederick Banting and John James Richard Macleod "for the discovery of insulin".^[1]

How insulin was named

The word insulin comes from Latin insula, meaning island (referring to the islets of Langerhans where it is produced). The term was coined in 1914.^[2]

Statistics

According to the CDC, 10% of the population over age 20 has diabetes. It is the sixth leading cause of death in the United States.^[3]

Clinical Trials

For a list of government-sponsored clinical trials involving insulin, visit here.

Interesting Facts

• The following Nobel Prizes have been awarded for work on insulin:^[4]
  • 1923 Nobel Prize to Frederick Grant Banting and John James Richard MacLeod for the discovery of insulin
  • 1958 to Frederick Sanger "for his work on the structure of proteins, especially that of insulin"
  • Medicine 1977 to Rosalyn Yalow "for the development of radioimmunoassays of peptide hormones"

• Insulin used to be an extract from the pancreases of animals, including pigs, dogs, and cows. Today, most insulin is synthesized in a form exactly the same as human insulin using recombinant DNA technology.

References

1. ↑ Nobel Prize Foundation Web site. The Nobel Prize in Physiology or Medicine 1923.
2. ↑ Merriam-Webster Online. Insulin.
3. ↑ CDC, National Center for Health Statistics. FastStats: Diabetes.
4. ↑ Nobel Prize Foundation Web site. Nobel Prizes.

External Links

American Association of Diabetes Educators

American Diabetes Association

Food and Drug Administration: Insulin Information Page

Related Accredited Articles

1. In Brief: Gestational Diabetes
2. Content from Harvard Medical School