Insulin And How It Works In The Body

Insulin plays a very important role in the metabolic process. It is a hormone that is produced in the pancreas and works in opposition with glucagon to control the blood glucose levels in the body. Insulin itself is a molecule that is composed of two polypeptide chains that are generated by a precursor molecule known as proinsulin. Problems or mutations in the proinsulin gene or the processing of proinsulin into insulin are linked to the early development of type 1 diabetes.1  Understanding the role of insulin helps to understand the importance that food management and lifestyle choices, as well as insulin therapy, can play in the management of all types of diabetes.

Insulin The Storage Trigger

Insulin is produced in the beta cells in the islets of the pancreas in response to elevated levels of blood glucose. This occurs after eating and during digestion as the glucose crosses the intestinal membrane in the digestive tract to enter the bloodstream. Once in the blood it circulates through the body with some glucose immediately used by the cells for energy. All cells in the body need glucose to function and glucose has to be available at all times, even when the body is in a fasting state.

In a normal functioning system the insulin is produced by the pancreas in a steady flow to prevent the pancreas from producing glucagon. Glucagon is the opposing hormone to insulin that tells the body to use the stored fat supplies in the body cells when glucose levels are low in the blood. Since insulin is present the cells first use glucose that is in the blood. When this level drops hunger is initiated which causes the person to eat, supplying more blood glucose through the digestive system and absorption of the sugars consumed. If a person does not eat, the pancreas begins to produce higher levels of glucagon and lower levels of insulin, triggering the internal breakdown of the stored fatty tissue and glycogen.

When insulin is not produced in the pancreas, in the case of type 1 diabetes, or when the insulin present is not recognized by the other cells in the body, blood glucose regulation is impossible. The body cells cannot use the glucose in the blood stream and begin to break down the stored energy deposits. This occurs despite the presence of very high levels of both insulin and blood glucose in type 2 diabetics.

Genetic factors are now seen as a possible cause of this type of insulin resistance that leads to elevated fasting plasma glucose levels and the risk of developing type 2 diabetes.

In studies, melatonin and circadian rhythm regulation was seen as a possible link to blood glucose homeostatis or regulation. This may indicate that those individuals with risk factors for developing hyperglycemia or diabetes could be genetically tested to determine their risks factors through the presence of a specific MT2, a melatonin receptor that is found in the pancreatic islet beta cells.2

Insulin and Other Organs

Insulin, as a hormone, has a far reaching impact on many different organs and tissues in the body. When there is a lack of insulin or a resistance to the insulin present in the body there is a risk of central nervous system depression which can lead to a coma and death in extreme circumstances.

Initially with type 2 diabetes the symptoms noted by the individual are due to the lack of insulin or the insulin resistance. This includes the constant hunger reported by individuals with diabetes. This hunger may be triggered both by the presence of elevated levels of glucagon or low levels of insulin. Although people are eating constantly they are also subject to rapid weight loss. The body is literally breaking down the fatty tissues despite the presence of normal or elevated blood glucose levels. This breaks down both muscle and actual fat deposits.

The high levels of blood glucose in the blood and the body’s inability to utilize the glucose present places additional stress on the filtration system of the kidneys. The kidneys will experience a high level of glucose in the tubule lumen, which will in turn trigger more frequent urination. The excessive glucose in the urine can lead to more frequent urinary tract infections and increased risk of kidney failure.

Increased risk of cardiovascular disease, which may be increased for up to 15 years prior to the diagnosis of diabetes, is common.3 This is partially due to the increase in osmotic blood pressure that occurs when the body is constantly dehydrated through the frequent urination. This dehydration also triggers the chronic thirst that most diabetics experience when their blood glucose is not regulated.

Poor circulation can occur due to a decrease in total blood volume due to cellular dehydration. As the blood becomes less hydrate there is less overall blood movement to the external limbs of the body. The hands, fingers, feet and toes may feel constantly cold, or there may be a loss of sensation in the limbs. In severe cases the poor circulation coupled with poor wound healing can lead to serious complications such as gangrene and increased risk of limb amputation.

Insulin plays an important role in the brain as well. Insulin is required by the cells in the brain for a variety of functions, most notably regulation of body temperature control and the ability to regulate food intake. There is additional research that indicates that insulin may play a much larger role in the overall energy homeostasis which is required to maintain a balance within and between all systems of the body.

Insulin Therapy

Insulin therapy is required for all patients that are diagnosed with type 1 diabetes since the body lacks the ability to produce insulin on its own. Individuals can take insulin several times a day through injections or insulin pumps that are surgically implanted into the body. This prevents the need for injections but still requires regular monitoring and blood tests to ensure the blood glucose level is within a normal range. The insulin pumps may be sensor augmented, which has shown to work with both children and adults to maintain a constant glycated hemoglobin level in the blood. In studies the sensor augmented pumps were much more effective than regular blood monitoring and injection in all subjects without any changes in weight gain or hypoglycemia. 4

Individuals with type 2 diabetes, gestational diabetes or prediabetes may not require insulin therapy but may be able to control their blood glucose levels through diet and exercise as well as through weight reduction and maintenance. However, some individuals with type 2 diabetes may be required to use insulin tablets, or less commonly the injections, to regulate their blood glucose levels.

There are several different types of insulin that can be prescribed based on the needs of the individual. These range from rapid acting insulin that is in the blood and active within 5 minutes of injection to long acting insulin which takes longer to act, about 6 to 10 hours, but is highly effective in managing blood glucose levels for up to 24 hours.

References

1 Steiner, D. F., Park, S. Y., Stoy, J., et al. (2009). A brief perspective on insulin production. Diabetes, Obesity and Metabolism , 189-196.

2 Bouatia-Naji, N., Bonneford, A., Cavalcanti-Proenca, C., et al. (2008). A variant near MTNR1B is associated with increased fasting plasma glucose levels and type 2 diabetes risk. Nature Genetics , 89-94.

3 Schnell, O., & Standl, E. (2006). IMPAIRED GLUCOSE TOLERANCE, DIABETES, AND CARDIOVASCULAR DISEASE. Endocrine Practice , 16-19.

4 Bergenstal, R. M., Tamborlane, W. V., Ahmann, A., et al. (2010). Effectiveness of Sensor-Augmented Insulin-Pump Therapy in Type 1 Diabetes. The New England Journal of Medication , 311-320.

This article was originally published July 12, 2012 and last revision and update of it was 9/10/2015.