The endocrine glands are glands that manufacture one or more hormones
and secrete them directly into the bloodstream. These hormones are then
carried throughout the body where they influence only those cells that have
receptor sites specific to them. Endocrine glands, unlike exocrine
glands, do not have ducts along which their products are carried. The
word endocrine is derived from the Greek terms "endo," meaning within, and
"krine," meaning to separate or secrete.
Although there are eight major endocrine glands scattered throughout the
body, they are still considered to be one system, the endocrine
system because they have similar functions, similar mechanisms of influence,
and many important interrelationships. The eight major endocrine glands
Some glands also have non-endocrine regions that have functions other than
hormone secretion. For example, the pancreas has a major exocrine portion
that secretes digestive enzymes and an endocrine portion that secretes hormones.
The ovaries and testes secrete hormones and also produce the ova
and sperm. Some organs, such as the stomach,
intestines, and heart,
produce hormones, but their primary function is not hormone secretion.