How insulin works

Last Updated: 2021-03-23

Insulin is a hormone made by the pancreas, one of the body’s endocrine organs. Insulin assists the body in turning blood sugar, or glucose, into energy—this process plays a significant role in the body’s metabolism and various aspects of memory and cognition. It also helps the body accumulate and use energy stores for use at a later time when the body demands it. Each organ differs in the way they use fuel to meet their energy needs, such as the brain, adipose tissue, or fat cells, muscles, kidney, and liver. Over the last few decades, researchers have determined that insulin affects the body’s energy stores and eating behavior by way of the central nervous system (CNS).

How does insulin regulate energy and brain function?

After a person eats, blood glucose increases—this rise in blood sugar triggers the pancreas to secrete insulin into the bloodstream. Insulin travels through the circulatory system to the body’s cells—it tells the cells to open up and let the glucose inside. Once within, the cells turn glucose into energy or store it for later use. The body cannot utilize or store glucose without insulin—instead, the glucose stays circulating in the blood.

Pancreas

The pancreas is about 4.7 to 7.1 inches (about 12 to 18 centimeters) long and weighs roughly 70 to 100 grams—about the weight of one medium sized banana. The pancreas does not look like a banana, however. It is made up of a head, a body, and a pointy tail. The position of the pancreas is behind the stomach in the upper abdomen.

The two main functions of the pancreas are:

• To produce the enzymes that break down foods in the intestine
• To produce and secrete the hormones that regulate blood sugar levels

Insulin and glucagon are the two essential hormones that orchestrate energy storage and utilization—they are produced by the islet cells in the pancreas. Islet cells are in clusters throughout the pancreas. Insulin and glucagon are a part of a feedback system that keeps blood sugar levels stable. The pancreas releases insulin when blood glucose levels are high; on the other hand, glucagon is released when the concentration of blood glucose falls too low. Glucagon causes the stored glycogen in the liver to convert to glucose, which is then released for use in the bloodstream.

Insulin and disorders of the pancreas

Diabetes mellitus is an underdiagnosed disorder that affects over 9% of the population in the United States. According to the American Diabetes Association, over 1 million new cases of diabetes are diagnosed in the United States each year.

Types of diabetes

The most common types of diabetes are:

• Type 1
• Type 2
• Gestational diabetes

Type 1 diabetes

In type 1 diabetes, the pancreas is not making the needed insulin. The immune system attacks and destroys the cells in the pancreas that produce insulin—this is known as autoimmunity. Type 1 diabetes is diagnosed in children and young adults, although it can arise at any age.

Type 2 diabetes

In type 2 diabetes the pancreas does not make enough insulin or use insulin efficiently. People can develop type 2 diabetes at any age, even during childhood; however, this type of diabetes most often occurs in adults. Type 2 is the most common type of diabetes.

Gestational diabetes

Gestational diabetes occurs during pregnancy in some women. Most of the time, this type of diabetes will go away after the infant is born. If a woman has gestational diabetes, they have a greater chance of developing type 2 diabetes later in life. Sometimes the diabetes diagnosed during pregnancy is type 2 diabetes.

Other types of diabetes

Less common types include monogenic diabetes, which is an inherited form of diabetes, and cystic fibrosis-related diabetes.

Treatment of insulin disorders

A person can develop hyperglycemia when the pancreas produces an insufficient amount of insulin or the body’s cells are resistant to the effects of insulin, termed as insulin resistance. Complications can occur if the blood sugar stays elevated for extended periods of time.

Each person’s treatment will vary, not only on the type of diabetes but also more individual-specific treatment differences. The aim of diabetes therapy is to keep blood glucose levels near to normal as possible.

Treatment and education should address medical, lifestyle (exercise and diet), and psychosocial issues. People with insulin insufficiency or dysregulation of the insulin/glucagon axis, such as in type 1 diabetes and type 2 diabetes, are intolerant to carbohydrates. Therefore, restriction of carbohydrates should play an integral role in managing these conditions. Diabetes education, such as knowing how insulin works, is also an essential part of self-management.

Treatment of type 1 diabetes

People with type 1 diabetes make little to no insulin because the beta cells in their pancreas are damaged or destroyed. Therefore, these individuals will need insulin injections to allow their body to process glucose and avoid complications from hyperglycemia.

Treatment of type 2 diabetes

People with type 2 diabetes do not respond well to the insulin produced by the pancreas, or they are insulin resistant. Type 2 diabetes is oftentimes managed with oral medication and lifestyle changes, such as diet and exercise. Sometimes supplemental insulin injections are needed to process the sugar adequately.

Types of insulin

Endogenous insulin refers to the insulin made inside the body by the pancreas. Exogenous insulin refers to the insulin made or retrieved from outside of the body. Exogenous insulin is the type of insulin injected or infused via an insulin pump. Many different types of insulin are available through the pharmacy—a prescription and specific instructions from a health-care provider are required.

Exogenous insulins differ by:

• How they are made or where they are retrieved from
• The duration of action—how long they work
• Their onset of action—how quickly it starts working
• When the action peaks—when they are most effective

Rapid-acting insulin

• Begins to work about 15 minutes after injection
• Peaks in about 1 hour
• Continues to work for 2 to 4 hours
• Types: Insulin glulisine (Apidra), insulin lispro (Humalog), and insulin aspart (NovoLog)

Regular or short-acting insulin

• Usually reaches the bloodstream within 30 minutes after injection
• Peaks anywhere from 2 to 3 hours after injection
• Is effective for approximately 3 to 6 hours
• Types: Humulin R, Novolin R

Intermediate-acting insulin

• Generally reaches the bloodstream about 2 to 4 hours after injection
• Peaks 4 to 12 hours later
• Is effective for about 12 to 18 hours
• Types: NPH (Humulin N, Novolin N)

Long-acting insulin

• Reaches the bloodstream several hours after injection
• Tends to lower glucose levels fairly evenly over a 24-hour period
• Types: Insulin detemir (Levemir) and insulin glargine (Lantus)

Premixed insulin

Premixed insulin benefits people who have difficulty drawing up insulin out of two bottles and drawing up accurate doses. Premixed insulin is also convenient for people whose diabetes has been maintained on this combination.

How to administer insulin

Insulin can be administered by syringe, pen, or pump according to the person’s preference and health-care provider’s advice.

An insulin pen is convenient and portable; it is a single unit that combines a very fine needle and an insulin cartridge—this makes it easy to give different kinds of insulin at different times of the day. Each type of insulin needs a separate pen.

Insulin syringes also have small needles with a special coating to decrease discomfort upon administration. If the health-care provider prescribes two types of insulin at the same time, the insulin can be drawn up into one syringe, or the insulin may come premixed. Caution is advised when mixing insulin types—detailed instructions must be followed for how to prepare each dose.

Insulin pumps that are worn outside of the body, are a reliable, efficient way to deliver intensive insulin therapy. The device comprises a small catheter, which is inserted under the skin, and a pump, which is about the size of a pager. The pump has an insulin storage and can be programmed to give small quantities of insulin on a routine schedule. If extra doses of insulin are needed, such as at meal times, the person presses a button on the device.

Insulin safety tips

• Too much insulin can lead to hypoglycemia, drop in blood glucose levels.
• Insulin cannot be taken orally.
• Insulin needles are not shared and need to be disposed in a hard container, such as a laundry detergent bottle or sharps container.
• Changing or stopping insulin should not be done without speaking to a health-care provider.
• Always check the expiration date of any medication.
• Plan for emergencies and determine what is needed in a first-aid kit and for travel.