Insulin
Insulin is a hormone made mainly by beta cells in the pancreas. It helps regulate blood glucose by signaling cells to take up, store, and use glucose, and it is central to metabolism, diabetes, and many forms of diabetes treatment.
What insulin is
Insulin is a peptide hormone produced mainly by beta cells in the islets of the pancreas. Its best-known job is helping control blood glucose, but it also affects fat storage, protein metabolism, liver glucose production, and overall energy balance. It is both a natural hormone and, in medicine, a treatment for some people with diabetes.
Blood glucose control
After a meal, carbohydrates are digested into glucose and other sugars that enter the bloodstream. Rising blood glucose signals beta cells to release insulin. Insulin helps muscle, fat, and other tissues take up glucose, encourages the liver and muscles to store glucose as glycogen, and reduces glucose release from the liver when energy is already available.
Insulin and glucagon
Insulin works in balance with glucagon, another pancreatic hormone. Insulin generally helps lower blood glucose when levels are high. Glucagon helps raise blood glucose when levels are low by signaling the liver to release stored glucose or make new glucose. This push-and-pull system helps keep energy available between meals and during activity.
How cells respond
Insulin binds to insulin receptors on target cells and starts signaling pathways inside the cell. In many tissues, this helps move glucose transporters to the cell surface so glucose can enter. Insulin also changes enzyme activity and gene expression related to storage, growth, and fuel use. The response is not the same in every tissue.
Type 1 diabetes
In type 1 diabetes, the immune system destroys many insulin-producing beta cells. Without enough insulin, glucose stays in the blood while cells cannot use it properly, and the body can shift toward dangerous ketone production. People with type 1 diabetes need insulin treatment to survive.
Type 2 diabetes and insulin resistance
In type 2 diabetes, the body may still make insulin, especially early on, but cells become less responsive to it. This is called insulin resistance. Over time, beta cells may not keep up with demand. Treatment may involve food choices, activity, weight management, non-insulin medicines, insulin therapy, or combinations depending on the person and disease stage.
Insulin as medicine
Medical insulin is used to replace or supplement the body's insulin. Different formulations act at different speeds and durations, such as rapid-acting, short-acting, intermediate-acting, long-acting, or ultra-long-acting insulin. It may be delivered by syringe, pen, pump, or other systems. Dosing must match meals, activity, illness, glucose readings, and medical guidance.
Low and high blood glucose
Too little effective insulin can contribute to high blood glucose, dehydration, fatigue, blurred vision, and, in severe cases, diabetic ketoacidosis or hyperosmolar crisis. Too much insulin relative to food, activity, or need can cause low blood glucose, or hypoglycemia, which may bring shakiness, sweating, confusion, seizures, or loss of consciousness.
Discovery and impact
The discovery and medical use of insulin in the early 20th century transformed type 1 diabetes from a rapidly fatal disease into a manageable chronic condition for many people. Since then, insulin has evolved from animal-derived preparations to human insulin, analogs, pens, pumps, continuous glucose monitoring, and automated insulin-delivery systems.
Why it matters
Insulin matters because it connects everyday eating to cellular energy. It shows how hormones, metabolism, the immune system, technology, and public health meet in one molecule. Understanding insulin helps readers make sense of diabetes, blood glucose testing, hypoglycemia, insulin resistance, hormone signaling, and why access to insulin is a life-or-death issue for many people.