The word “hormone” (early 20th century) is derived from the Greek word hormon, present participle of horman, meaning to impel, or set in motion.
What are hormones?
Hormones are chemical messengers that travel around the body in the bloodstream that control much of our physical lives – when we sleep, eat or conceive. They are produced in specific sites, but each hormone affects only cells that have the correct receptor molecules on their surface.
These cells may be in another part of the body. This receptor mechanism – also called a “lock and key” – allows hormones to circulate throughout the body without triggering reactions in every cell. Many other body chemicals use the same technique to target their message.
Hormones help to maintain balance in the body – homeostasis, the other control mechanism being the nervous system. Hormonal changes tend to be slower and longer-lived than nervous changes.
Metabolism, growth, sleep, reproduction, the balance of body fluids and our response to stress are all hormone-controlled.
The levels of hormones in our blood fluctuate during the day in a prearranged way, so we can take advantage of daylight for maximum activity and wind down as darkness falls.
Unexpected exertion or trauma causes more dramatic changes. The overall pattern is coordinated by the hypothalamus using feedback mechanisms that detect hormone levels and trigger messages from the pituitary gland to stimulate or inhibit hormone production.
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