In this section...
At its simplest, a hormone is a chemical messenger
from one cell (or
group of cells) to another. Hormones are released (secreted) in the
body and have an effect on other parts of the body. The effect is to
communicate with possibly distant parts of the body. So for example,
the adrenal glands may secrete adrenalin, which has an effect on several
different organs. An endocrine gland is a gland which secretes hormones
(note that not all glands are classified as endocrine glands; for example,
sweat glands or lymph glands are not endocrine glands).
Hormones are found in all organisms with more than one cell, and so
they are found in plants and animals. They influence or control a wide
range of physiological activities, such as growth, development, puberty,
level of alertness, sugar regulation and appetite, bone growth, etc.
You also find that problems with hormones and the way they work contribute
to some of the major diseases of mankind; for example, diabetes, thyroid
conditions, pituitary conditions, some sexual problems, some neurological
problems, appetite and obesity, bone problems, cancer, etc.
There are whole sub-specialities devoted to specific areas where hormones
work. For example:
There are numerous textbooks which can give background information
on endocrinology. For example, an online textbook can be found at:
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