Functions of insulin
Last updated on June 24th, 2016
Insulin is a protein-based hormone that is made by the beta cells of the pancreas. Most people know that insulin is the hormone that helps the body’s cells put glucose into the cells for use as cellular fuel. In the absence of insulin, the cells do not have enough biochemical energy so they must use other nutrients in order to function. Without insulin, life-threatening complications can occur due to high blood sugar levels.
Insulin and Metabolism
When a person eats a meal containing glucose (or any other carbohydrate), the pancreas secretes insulin so that the glucose absorbed by the cells can be used for cellular metabolism. Insulin essential for cell metabolism and, without it, the individual would die.
In type 1 diabetics, the pancreas cannot secrete insulin so the blood sugars go higher. The cells do not get enough glucose for cellular metabolism. In type 2 diabetes, there is usually enough insulin secreted; however, the cells are resistant to insulin and glucose cannot get into the cells for cellular metabolism.
If diabetes is left unchecked, glucose builds up in the bloodstream and doesn’t get passed along to the cells nor is it stored as glycogen in the liver. This can damage many bodily organs and tissues, including the eyes, nerves, blood vessels, and kidneys.
Insulin replacement is necessary for type 1 diabetes because these types of diabetics don’t get enough insulin from the pancreas to do its job. In some cases, type 2 diabetics need insulin because their pancreas has been overworked and is tired, damaging the beta cells of the pancreas. Insulin is injected into the fatty tissue, usually in the abdomen; however, other good sites for injection of insulin is the buttocks, thighs, or upper arms.
Insulin’s action on the Digestive System
When a person eats a meal, food is allowed to travel to the stomach and the small intestines. There the food undergoes a breakdown into small nutrient particles that are then absorbed into the blood. In response to this absorption of carbohydrate nutrients, the pancreas secretes insulin in order to make use of the glucose for cellular metabolism. The pancreas is considered part of the digestive system as well as the endocrine system.
Insulin allows the fat cells, muscle cells, and liver cells to keep glucose in storage until it is later needed for cellular fuel. At the same time, the liver makes less glucose and instead stores it as glycogen. This allows the blood sugars to remain stable. Between meals, the liver breaks down its glycogen stores so that there will always be enough glucose in the bloodstream.
Insulin and the Circulatory System
Insulin is secreted into the bloodstream and helps the cells of the body make use of glucose. It is the responsibility of the circulatory system to provide the insulin for all the cells of the body. As long as enough insulin is produced by the body, the glucose is able to be used and the cells of the body thrive.
If there isn’t enough insulin in the circulatory system, glucose levels go up and there can be complications, such as diabetic nephropathy (kidney damage), diabetic retinopathy (eye damage), diabetic neuropathy (nerve damage), and heart disease.
A lack of insulin in the bloodstream results in starvation of the cells. As the cells can’t make use of glucose, they start to break down fat to be used as cellular fuel. If glucose in the bloodstream becomes extremely high, ketones can build up in the body. Ketones are the metabolic byproduct of other sources of fuel the body is using. When ketones build up, there can be obvious symptoms, such as a dry mouth, nausea, vomiting, and a sweetness in the breath. When this happens, it is called diabetic ketoacidosis.
Insulin and Storage
Insulin is the hormone responsible for the storage of glucose into fatty tissue, muscle tissue, and liver tissue, among others. It does this through a process called facilitated diffusion. There are hexose transporters on the walls of the cells throughout the body that are a part of this type of facilitated diffusion.
When the concentration of insulin is decreased, transporters inside cytoplasmic vesicles, GLUT4 transporters (the major transporter for blood sugar uptake) are activated. Insulin must bind to these transporters in order to allow for the passage of glucose into the cell. What glucose isn’t used to make fuel is then stored inside the cells. Some cells store glucose better than others, including the fat cells, liver cells, and muscle cells.
There are other cells of the body that don’t need insulin in order to take up glucose for storage. They don’t use the GLUT4 transporter but use other types of transporters for glucose uptake that aren’t reliant upon insulin to get the glucose into the cells.
Insulin and the Liver
A great deal of glucose absorbed into the bloodstream is put into liver cells, also known as hepatocytes. The hepatocytes have the primary responsibility of turning the glucose into its storage form, a long polymer known as glycogen.
Insulin affects the liver in several ways. It causes the activation of hexokinase, which is an enzyme that phosphorylates glucose so that it becomes unable to leave the cells. Insulin also activates other enzymes necessary for the storage of glycogen in the liver. Two of these enzymes are called glycogen synthase and phosphofructokinase. In its general role on the liver, insulin is responsible for the storage of glucose within the liver.
Insulin and Glucose Concentrations
Insulin is responsible for regulating the glucose concentration inside the bloodstream. There is a direct relationship between glucose and insulin. As the glucose level falls, the insulin level also falls so that the individual doesn’t get hypoglycemia. As the glucose level rises, so does the insulin level. In this way, the insulin can start to act to decrease the glucose concentrations in the bloodstream.
Insulin and Fatty Acids
Insulin helps synthesize fatty acids in the liver cells. If the glycogen levels make up at least 5 percent of the mass of the liver, the glycogen synthesis is suppressed and fatty acids are instead made by the liver to be used to make the lipid layer of the cells of the body. The fatty acids are then taken out of the liver and are transferred to lipoproteins, which allow for the transportation of the fatty acids to make cells or to be stored inside fat cells as fat.
- The effects of insulin on the body. http://www.healthline.com/health/diabetes/insulin-effects-on-body. Accessed 5/16/16.
- Physiological Effects of Insulin. http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/pancreas/insulin_phys.html. Accessed 5/16/16.