Chemical substance that is produced by a specialized tissue formation called an
endocrine gland. The substance is secreted directly into
blood-stream, other body fluids or into adjacent tissues. The purpose of
hormones is to regulate metabolic activity of some other organs or tissues
of the body.
The rate of production of a given hormone is most commonly regulated
by a mechanism called a [negative feedback loop]?.
The notion "endocrine" is contrasted with "exocrine"
which means a specialized gland with a distinct secretory duct. Examples
of exocrine are salivary or sweat glands and of endocrine glands are thyroid and adrenal glands.
The most important hormones :
Some special group of hormones are trophic hormones that act as stimulants of hormone production of other endocrine glands. For example thyroid stimulating hormone (TSH) causes growth and increased activity of another endocrine gland - thyroid, hence increasing output of thyroid hormones.
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