Insulin is a endocrine hormone secreted by the pancreas that helps transport glucose, or blood sugar, from the bloodstream to the cells, which then use glucose as energy or store it as glycogen or fat. Diabetics and people with insulin resistance do not produce insulin or cannot receive the signals from insulin. In some cases, a diet can control or even reverse the condition. In other cases, insulin injections or sprays are necessary. Insulin given in the form of an injection or nasally work the same way as the body's own insulin.
The Role of Insulin in Metabolism
When you ingest food, the food breaks down into carbohydrates, fat and protein in the digestive system. Carbohydrates further convert into glucose, which is released into the bloodstream. Protein breaks down into amino acids. Fat goes through a more complicated process during which it is disassembled and then assembled again but now covered with a protein coating that allows it to enter the bloodstream. When these compounds enter the bloodstream, the pancreas responds by secreting insulin. Insulin helps move glucose from the bloodstream to the body's cells. When the bloodstream contains only low amounts of energy sources, the pancreas stops secreting insulin.
Diabetes and Insulin Resistance
In patients with diabetes, insulin cannot do its job properly. Type 1 diabetics have an autoimmune response that destroys the pancreas' ability to produce insulin. Type 2 diabetes and insulin resistance negatively affect cell receptors for insulin, making the presence of insulin futile. Insulin is present in the blood but cannot get its message through to the cells. Type 2 diabetes and insulin resistance are usually controlled through a diet that prevents extreme fluctuations in blood sugar and insulin levels. Type 1 diabetes normally cannot be controlled through diet alone. Individuals with type 1 diabetes depend on insulin rejections or insulin taken nasally to avoid accumulation of blood sugar in the bloodstream.
The Function of Insulin and Insulin Receptors
Insulin removes glucose from the bloodstream by binding to receptors that penetrate the membranes of the body's muscle and fat cells. When insulin binds to the insulin receptors, this causes a glucose transporter, known as GLUT-4, to move from inside the cell to the cell membrane. Once GLUT-4 has become embedded in the cell membrane, it opens up channels that let glucose pass from the blood to the liquid inside the cell, where it can be used as a fuel to produce energy. When glucose reaches the inside of the body's cells, blood sugar levels drop significantly.
The GLUT-4 Glucose Transporter in the Absence of Insulin
If the blood concentrations of insulin are low, or the insulin receptor does not transfer the insulin signal, the GLUT-4 remains inside the cell's liquid. When GLUT-4 is not embedded in the cell membrane, it cannot transfer glucose into the cell. If the pancreas does not produce insulin, the insulin required for muscle and fat cells to absorb glucose from the bloodstream must be provided externally. Once externally provided insulin has entered the bloodstream, it works in the same way as insulin secreted by the pancreas.
References
- American Diebetes Association: Diebetes Basics
- MayoClinic.com; Diabetes; March 9, 2011
- Fox News.com; Diabetic Teens Skipping Insulin to Lose Weight; Associated Press; June 17, 2007
- Colorado State University: Physiologic Effects of Insulin
- MedBio.info; Insulin's Mechanism of Action; Prof. Emeritus Robert S. Horn
