endorphin

If you’re getting sore and tired while running, don’t worry! Just wait for your endorphins to kick in. An endorphin is a hormone that your body produces to ease pain and make you feel calm and happy.

Endorphins are sometimes called "natural pain killers," since that's the way they act in the body. Things like stress and exercise can stimulate the release of endorphins. A “runner’s high” happens when a runner gets a rush of endorphins. Your nervous system and pituitary gland send endorphins to your brain, where they bind to special receptors. It's similar to what happens when you take a painkilling medication. In fact, the word endorphin is a blend of “endogenous” (meaning "inside the body") and “morphine" (a medication that relieves pain).

Definitions of endorphin
1

n a neurochemical occurring naturally in the brain and having analgesic properties

Types:
beta endorphin
an endorphin produced by the pituitary gland that suppresses pain
enkephalin
an endorphin having opiate qualities that occurs in the brain and spinal cord and elsewhere
Type of:
peptide
amide combining the amino group of one amino acid with the carboxyl group of another; usually obtained by partial hydrolysis of protein
neurochemical
any organic substance that occurs in neural activity

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