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Physiologic effects of Insulin

Insulin is secreted by a small group of cells in the pancreas. They are called beta cells, located in the islets of Langerhans. The islets of Langerhans are islands of four types of cells (alpha, beta, delta, and F) surrounded by pancreatic ancini. Drag your cursor over the map to identify cells and their related products.

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The pancreatic islet cell that is responsible for secreting insulin is the alpha cell.

Insulin has the following important effects on body tissues:

It promotes anabolism – the metabolic process that constructs complex molecules from simple ones.
It inhibits the conversion of glycogen stored in the liver or muscle cells into glucose.
It blocks the formation of glucose from non-carbohydrate sources such as amino acids.
It enhances protein synthesis by stimulating the entry of amino acids into cells.
It enhances fat storage and prevents fats from being used for energy.

The term "endogenous" insulin refers to insulin produced by beta cells in the pancreas. "Exogenous" insulin is a term used to describe pharmaceutical insulin. Counter-regulatory hormones are hormones that block the effects of insulin, thus increasing blood glucose. Important counter-regulatory hormones include: glucagon, epinephrine, norepinephrine, growth hormone, and cortisol. Blood glucose management in diabetes must account for the release of one or more of these counter-regulatory hormones throughout the day.

Insulin is essential for normal carbohydrate, protein, and fat metabolism. People with type 1 diabetes do not produce enough insulin to sustain life and therefore depend on exogenous insulin for survival. Although people with type 2 diabetes are not dependent on exogenous insulin for survival, over time many people with type 2 diabetes have decreased insulin production and may need exogenous supplemental insulin for adequate blood glucose control. This is especially true during times of stress or illness. This is why the designation "type 2" diabetes has replaced the former term "non-insulin dependent diabetes mellitus."

The next page presents an in-depth look at insulin production at a cellular level; an "Interactive Beta Cell Tour." Many of the substances involved in glucose and protein metabolism, as well as the chemical ions (calcium, potassium and sodium, for example) are described and their actions shown.