Insulin is a hormone produced by beta cells in the pancreas . It regulates blood sugar (glucose) levels, increasing glucose uptake in fat, muscle, and liver tissues to maintain energy balance. When blood glucose rises, insulin is secreted; when it falls, insulin secretion stops, and the liver releases glucose. Insulin stimulates glucose transporters to move to the cell membrane, facilitating glucose uptake. Insufficient insulin production leads to diabetes mellitus , requiring insulin injections, which are now primarily human insulin produced using recombinant DNA technology.

Where in the body is insulin made?

Insulin , a hormone that regulates blood sugar levels, is produced by the beta cells of the islets of Langerhans in the pancreas. After a meal, when blood glucose levels rise, insulin is secreted. As blood glucose levels fall, insulin secretion stops, and the liver releases glucose into the blood. The inability of the islet cells to produce insulin, or failure to produce sufficient amounts, causes diabetes mellitus .

What is the main function of insulin in the body?

The primary role of insulin is to regulate glucose levels in the blood. Produced by the pancreas' beta cells, insulin prompts cells to absorb glucose from the blood for energy or storage as glycogen. After a meal, as blood glucose rises, insulin is released; conversely, insulin secretion decreases as blood glucose levels fall. Insulin stimulates glucose uptake in adipose (fat), muscle, and liver tissues, which is crucial for nutrient metabolism and storage. Insufficient insulin production leads to diabetes mellitus , requiring insulin therapy to maintain normal blood glucose levels.

How does insulin affect blood sugar levels?

Insulin is a hormone produced in the pancreas that regulates blood glucose levels. After a meal, as blood glucose rises, insulin is secreted; conversely, as blood glucose levels fall, insulin secretion decreases. Insulin stimulates glucose uptake in fat, muscle, and liver tissues. In muscle tissue, insulin promotes glucose and amino acid transport into muscle cells, storing glucose as glycogen for energy. In liver cells, insulin increases glucose storage and reduces glucose production and release. Insufficient insulin production leads to diabetes mellitus, requiring insulin injections to maintain normal blood glucose levels.

What happens if the body does not make enough insulin?

When the body doesn't produce enough insulin , a hormone that regulates blood sugar (glucose) levels, it leads to a condition called diabetes mellitus . Insulin is secreted by beta cells in the pancreas and is essential for cells to uptake glucose from the blood for energy. Insufficient insulin results in hyperglycemia , or high blood sugar, as glucose can't enter cells effectively. This can cause symptoms such as increased thirst and frequent urination as the body tries to eliminate excess glucose through urine. Over time, diabetes can lead to serious health complications, including cardiovascular disease, nerve damage, kidney failure, and vision loss. Treatment typically involves insulin therapy to help regulate blood glucose levels.

How is insulin used as a treatment for diabetes?

Insulin is a hormone that regulates blood sugar levels, and inadequate insulin production leads to diabetes mellitus. Insulin therapy is essential for diabetics who do not produce it themselves. Before insulin was discovered in the 1920s, most patients died shortly after the onset of diabetes. Traditional insulin therapy involves regular hormone injections, tailored to individual needs. Modern treatments use recombinant DNA technology to produce human insulin, which can be short-acting or long-acting. The goal is to mimic the natural insulin secretion pattern: a constant low level plus a surge after each meal. This can be achieved with a daily long-acting insulin shot and a rapid-acting one before meals. Insulin pumps offer more control over administration rates. Patients on insulin may need to adjust their food intake based on activity levels, needing less insulin and more food as exercise increases.

Insulin

Introduction References & Edit History Related Topics

Images & Videos

Diagram showing how hormones from white adipose tissue, the gastrointestinal tract, and pancreatic islets of Langerhans affect organs such as the brain, stomach, pancreas, liver, adipose tissue, and muscle, with arrows illustrating hormone actions and physiological effects.

Ball-and-stick molecular model of insulin, with clusters of multicolored spheres representing atoms, connected and outlined in yellow against a dark background.

Diagram showing a cross-section of a pancreatic islet of Langerhans on the left, with alpha, beta, and delta cells labeled by color, and on the right, arrows illustrating paracrine interactions among these cell types through hormones glucagon, insulin, and somatostatin.

Learn about genetic engineering and how it is applied to microbes to genetically modify them for use in medicines, food, and fuel

At a Glance

insulin summary

Quick Facts

Key People:: Nicolas C. Paulescu; Sir Frederick Grant Banting; Charles H. Best; Frederick Sanger; Oskar Minkowski

Related Topics:: diabetes mellitus; pancreas; antidiabetic drug; diabetes insipidus; beta cell

See all related content

Insulin

hormone

Written by

Robert D. Utiger

Fact-checked by

Britannica Editors

Last updated

Nov. 12, 2026 •History

News •

Transplanted placental cells successfully detected in mouse pancreas after birth • Oct. 22, 2026, 4:24 PM ET (News-Medical)

Top Questions

What is insulin?
Insulin is a hormone produced by beta cells in the pancreas. It regulates blood sugar (glucose) levels, increasing glucose uptake in fat, muscle, and liver tissues to maintain energy balance.

When blood glucose rises, insulin is secreted; when it falls, insulin secretion stops, and the liver releases glucose. Insulin stimulates glucose transporters to move to the cell membrane, facilitating glucose uptake. Insufficient insulin production leads to diabetes mellitus, requiring insulin injections, which are now primarily human insulin produced using recombinant DNA technology.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Where in the body is insulin made?
Insulin, a hormone that regulates blood sugar levels, is produced by the beta cells of the islets of Langerhans in the pancreas. After a meal, when blood glucose levels rise, insulin is secreted. As blood glucose levels fall, insulin secretion stops, and the liver releases glucose into the blood. The inability of the islet cells to produce insulin, or failure to produce sufficient amounts, causes diabetes mellitus.
4 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What is the main function of insulin in the body?
The primary role of insulin is to regulate glucose levels in the blood. Produced by the pancreas' beta cells, insulin prompts cells to absorb glucose from the blood for energy or storage as glycogen.

After a meal, as blood glucose rises, insulin is released; conversely, insulin secretion decreases as blood glucose levels fall. Insulin stimulates glucose uptake in adipose (fat), muscle, and liver tissues, which is crucial for nutrient metabolism and storage. Insufficient insulin production leads to diabetes mellitus, requiring insulin therapy to maintain normal blood glucose levels.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How does insulin affect blood sugar levels?
Insulin is a hormone produced in the pancreas that regulates blood glucose levels. After a meal, as blood glucose rises, insulin is secreted; conversely, as blood glucose levels fall, insulin secretion decreases.

Insulin stimulates glucose uptake in fat, muscle, and liver tissues. In muscle tissue, insulin promotes glucose and amino acid transport into muscle cells, storing glucose as glycogen for energy. In liver cells, insulin increases glucose storage and reduces glucose production and release. Insufficient insulin production leads to diabetes mellitus, requiring insulin injections to maintain normal blood glucose levels.
2 Britannica Sources
1. diabetes mellitus: Type 2 diabetes mellitus
2. insulin
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What happens if the body does not make enough insulin?
When the body doesn't produce enough insulin, a hormone that regulates blood sugar (glucose) levels, it leads to a condition called diabetes mellitus. Insulin is secreted by beta cells in the pancreas and is essential for cells to uptake glucose from the blood for energy.

Insufficient insulin results in hyperglycemia, or high blood sugar, as glucose can't enter cells effectively. This can cause symptoms such as increased thirst and frequent urination as the body tries to eliminate excess glucose through urine. Over time, diabetes can lead to serious health complications, including cardiovascular disease, nerve damage, kidney failure, and vision loss. Treatment typically involves insulin therapy to help regulate blood glucose levels.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How is insulin used as a treatment for diabetes?
Insulin is a hormone that regulates blood sugar levels, and inadequate insulin production leads to diabetes mellitus. Insulin therapy is essential for diabetics who do not produce it themselves.

Before insulin was discovered in the 1920s, most patients died shortly after the onset of diabetes. Traditional insulin therapy involves regular hormone injections, tailored to individual needs. Modern treatments use recombinant DNA technology to produce human insulin, which can be short-acting or long-acting.

The goal is to mimic the natural insulin secretion pattern: a constant low level plus a surge after each meal. This can be achieved with a daily long-acting insulin shot and a rapid-acting one before meals. Insulin pumps offer more control over administration rates. Patients on insulin may need to adjust their food intake based on activity levels, needing less insulin and more food as exercise increases.
2 Britannica Sources
1. diabetes mellitus: Insulin therapies
2. insulin
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Insulin, hormone that regulates the level of sugar (glucose) in the blood and that is produced by the beta cells of the islets of Langerhans in the pancreas. Insulin is secreted when the level of blood glucose rises—as after a meal. When the level of blood glucose falls, secretion of insulin stops, and the liver releases glucose into the blood. Insulin was first reported in pancreatic extracts in 1921, having been identified by Canadian scientists Frederick G. Banting and Charles H. Best and by Romanian physiologist Nicolas C. Paulescu, who was working independently and called the substance “pancrein.” After Banting and Best isolated insulin, they began work to obtain a purified extract, which they accomplished with the help of Scottish physiologist J.J.R. Macleod and Canadian chemist James B. Collip. Banting and Macleod shared the 1923 Nobel Prize for Physiology or Medicine for their work.

Insulin is a protein composed of two chains, an A chain (with 21 amino acids) and a B chain (with 30 amino acids), which are linked together by sulfur atoms. Insulin is derived from a 74-amino-acid prohormone molecule called proinsulin. Proinsulin is relatively inactive, and under normal conditions only a small amount of it is secreted. In the endoplasmic reticulum of beta cells the proinsulin molecule is cleaved in two places, yielding the A and B chains of insulin and an intervening, biologically inactive C peptide. The A and B chains become linked together by two sulfur-sulfur (disulfide) bonds. Proinsulin, insulin, and C peptide are stored in granules in the beta cells, from which they are released into the capillaries of the islets in response to appropriate stimuli. These capillaries empty into the portal vein, which carries blood from the stomach, intestines, and pancreas to the liver. The pancreas of a normal adult contains approximately 200 units of insulin, and the average daily secretion of insulin into the circulation in healthy individuals ranges from 30 to 50 units.

Several factors stimulate insulin secretion, but by far the most important is the concentration of glucose in the arterial (oxygenated) blood that perfuses the islets. When blood glucose concentrations increase (i.e., following a meal), large amounts of glucose are taken up and metabolized by the beta cells, and the secretion of insulin increases. Conversely, as blood glucose concentrations decrease, the secretion of insulin decreases; however, even during fasting, small amounts of insulin are secreted. The secretion of insulin may also be stimulated by certain amino acids, fatty acids, keto acids (products of fatty acid oxidation), and several hormones secreted by the gastrointestinal tract. The secretion of insulin is inhibited by somatostatin and by activation of the sympathetic nervous system (the branch of the autonomic nervous system responsible for the fight-or-flight response).

Superficial arteries and veins of face and scalp, cardiovascular system, human anatomy, (Netter replacement project - SSC)

Britannica Quiz

The Human Body

Insulin acts primarily to stimulate glucose uptake by three tissues—adipose (fat), muscle, and liver—that are important in the metabolism and storage of nutrients. Like other protein hormones, insulin binds to specific receptors on the outer membrane of its target cells, thereby activating metabolic processes within the cells. A key action of insulin in these cells is to stimulate the translocation of glucose transporters (molecules that mediate cell uptake of glucose) from within the cell to the cell membrane.

In adipose tissue, insulin stimulates glucose uptake and utilization. The presence of glucose in adipose cells in turn leads to increased uptake of fatty acids from the circulation, increased synthesis of fatty acids in the cells, and increased esterification (when an acid molecule binds to an alcohol) of fatty acids with glycerol to form triglycerides, the storage form of fat. In addition, insulin is a potent inhibitor of the breakdown of triglycerides (lipolysis). This prevents the release of fatty acids and glycerol from fat cells, saving them for when they are needed by the body (e.g., when exercising or fasting). As serum insulin concentrations decrease, lipolysis and fatty acid release increase.

In muscle tissue, insulin stimulates the transport of glucose and amino acids into muscle cells. The glucose is stored as glycogen, a storage molecule that can be broken down to supply energy for muscle contraction during exercise and to supply energy during fasting. The amino acids transported into muscle cells in response to insulin stimulation are utilized for the synthesis of protein. In contrast, in the absence of insulin the protein of muscle cells is broken down to supply amino acids to the liver for transformation into glucose.

Insulin is not required for the transport of glucose into liver cells, but it has profound effects on glucose metabolism in these cells. It stimulates the formation of glycogen, and it inhibits the breakdown of glycogen (glycogenolysis) and the synthesis of glucose from amino acids and glycerol (gluconeogenesis). Therefore, the overall effect of insulin is to increase glucose storage and to decrease glucose production and release by the liver. These actions of insulin are opposed by glucagon, another pancreatic hormone produced by cells in the islets of Langerhans.

Explore Britannica Premium!

The trusted destination for professionals, college students, and lifelong learners.

Inadequate production of insulin is responsible for the condition called diabetes mellitus. Severe diabetics require periodic injections of insulin. The first insulin injections utilized hormone extracts from pigs, sheep, and cattle, but by the early 1980s certain strains of bacteria had been genetically modified to produce human insulin. Today the treatment of diabetes mellitus relies primarily on a form of human insulin that is made using recombinant DNA technology.

Robert D. Utiger

Insulin

News •

Thank you for signing up!