Hormone
Say it: HOR-mohn
A hormone is a chemical messenger released into the blood by a gland or cell that changes the activity of distant target cells with matching receptors.
Also: hormones
Definition
What is a hormone?
A hormone is a signaling molecule made by an endocrine gland, or by scattered endocrine cells in other organs, and carried in the bloodstream to the rest of the body. Although a hormone reaches almost every tissue, it acts only on target cells that have a receptor for it, and tiny amounts can have large effects. Hormones help control growth and development, metabolism, water and salt balance, reproduction, the response to stress, and mood.
Chemically, hormones fall into three classes. Amine hormones, such as epinephrine and thyroid hormones, are built from single amino acids. Peptide and protein hormones, such as insulin and growth hormone, are chains of amino acids. Steroid hormones, such as cortisol, estrogen and testosterone, are made from cholesterol. Water-soluble hormones cannot cross the cell membrane, so they bind receptors on the cell surface and act through second messengers such as cyclic AMP. Lipid-soluble steroid and thyroid hormones enter the cell, bind receptors inside it and change which genes are switched on.
Hormone release is usually kept in check by negative feedback, and it can be triggered by changes in blood chemistry, by other hormones or by nerve signals. Disorders such as diabetes and thyroid disease arise when a hormone is made in too large or too small an amount, or when target cells stop responding.
Word parts
Where does the word “hormone” come from?
- hormone
- setting in motion, urging onGreek hormōn, from horman
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Terms that go with it
- Endocrine systemThe endocrine system is the set of glands and cells that release hormones into the blood to regulate growth, metabolism, reproduction and more.
- ReceptorA receptor is a protein, on a cell's surface or inside it, that binds a specific signaling molecule and triggers a response in the cell.
- InsulinInsulin is a peptide hormone made by beta cells in the pancreas that lowers blood glucose by helping body cells take up and store sugar.
- CortisolCortisol is a steroid hormone made by the adrenal cortex that helps the body cope with stress, raises blood glucose and dampens inflammation.
- HomeostasisHomeostasis is the body's ability to keep internal conditions, such as temperature, blood glucose and pH, steady while conditions around it change.
- GlucagonGlucagon is a peptide hormone made by alpha cells of the pancreas that raises blood glucose, mainly by making the liver release glucose.
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