How Insulin Works in the Body

The Multiple Roles of This Vital Hormone

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Insulin is a hormone produced by the pancreas to help metabolize and use food for energy throughout the body. This is a key biological function, and so a problem with insulin can have a widespread effect on any or all of the tissues, organs, and systems of the body.

Insulin is so important to overall health, and even survival, that when there are problems with insulin production or utilization, as with diabetes, supplemental insulin often is needed throughout the day.

In fact, in the case of type 1 diabetes, an autoimmune disease in which no insulin is produced, supplemental insulin is vital. Supplemental insulin isn't always necessary for treating type 2 diabetes, in which insulin production is lower than normal and/or the body isn't able to use it efficiently—a condition called insulin resistance.

If you have either type of diabetes, learning how the naturally produced hormone works in the body can help you to understand why taking daily insulin shots or wearing an insulin pump or patch may be a key aspect of your treatment plan. It can be helpful to be familiar with the involvement insulin has in the metabolism and utilization of fats and proteins in the diet as well.

How Insulin is Produced

Insulin is produced by the pancreas, a glandlike organ nestled in the curve of the duodenum (the first part of the small intestine) just behind the stomach. The pancreas functions both as an exocrine gland and an endocrine gland.

The exocrine function of the pancreas basically is to help with digestion. It's in the role as an endocrine gland that the pancreas produces insulin, as well as another hormone called glucagon.

Insulin is produced by specialized beta cells in the pancreas, which are clustered into groups called islets of Langerhans. There are approximately one million islets in a healthy adult pancreas, taking up about 5 percent of the entire organ. (The pancreatic cells that produce glucagon are called alpha cells.)

How Insulin Works

Insulin is the energy storage hormone. After a meal, it helps the cells use carbs, fats, and protein as needed, and to store what's left (mainly as fat) for the future. The body breaks these nutrients down into sugar molecules, amino acid molecules, and lipid molecules, respectively. The body also can store and reassemble these molecules into more complex forms.

Carbohydrate Metabolism

Blood sugar levels rise when most foods are consumed, but they rise more rapidly and dramatically with carbohydrates. The digestive system releases glucose from foods and the glucose molecules are absorbed into the bloodstream. The rising glucose levels signal the pancreas to secrete insulin to clear glucose from the bloodstream.

To do this, insulin binds with insulin receptors on the surface of cells, acting like a key that opens the cells to receive glucose. There are insulin receptors on almost all tissues in the body, including muscle cells and fat cells.

Insulin receptors have two main components—the exterior and interior portions. The exterior portion extends outside the cell and binds with insulin. When this happens, the interior part of the receptor sends out a signal inside the cell for glucose transporters to mobilize to the surface and receive the glucose. As blood sugar and insulin levels decrease, the receptors empty and the glucose transporters go back into the cell.

When the body is functioning normally, the glucose derived from ingested carbohydrates gets cleared rapidly through this process. However, when there's no insulin or very low levels of insulin, this doesn't happen, leading to sustained high blood glucose levels.

Excess blood sugar also results when cells aren't able to use insulin properly. Insulin resistance can be due to a problem with the shape of the insulin (preventing receptor binding), not having enough insulin receptors, signaling problems, or glucose transporters not working properly. In addition, insulin resistance can occur as a result of excess body fat.

Fat Metabolism

Insulin has a major effect on fat metabolism. After a meal, insulin causes "extra" ingested fats and glucose to be stored as fat for future use.

Insulin also plays a key role in:

  • The liver. Insulin stimulates the creation and storage of glycogen from glucose. High insulin levels cause the liver to get saturated with glycogen. When this happens, the liver resists further storage. Glucose is used instead to create fatty acids that are converted into lipoproteins and released into the bloodstream. These break down into free fatty acids and are used in other tissues. Some tissues use these to create triglycerides.
  • Fat cells. Insulin stops the breakdown of fat and prevents the breakdown of triglycerides into fatty acids. When glucose enters these cells, it can be used to create a compound called glycerol. Glycerol can be combined with the excess free fatty acids from the liver to make triglycerides. This can cause triglycerides to build up in the fat cells.

Protein Metabolism

Insulin helps the amino acids in protein to enter cells. Without adequate insulin production, this process is hindered, making it difficult to build muscle mass.

Insulin also makes cells more receptive to potassium, magnesium, and phosphate. Known collectively as electrolytes, these minerals help conduct electricity within the body. In doing so, they influence muscle function, blood pH, and the amount of water in the body. An electrolyte imbalance can be worsened by high blood sugar levels as this can cause excessive urination (polyuria) with water and electrolyte loss.

A Word From Verywell

While insulin is primarily regarded as the hormone that regulates blood sugar, it also plays a key roles in the metabolism of the protein and fats in the food we eat and how they're utilized and stored. For people with type 1 diabetes, the absence of insulin cannot be helped, but it can be managed with supplemental insulin. For others, there are ways to help prevent problems with insulin that could lead to type 2 diabetes, including following a balanced, nutrient-rich diet, maintaining a healthy weight, exercising regularly, and taking other measures to live an overall healthy lifestyle.

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