Home > Encyclopedia of Science > Hormones

• Plant hormones
• Words to Know
• Important Hormones of the Human Body
• Animal hormones

Hormones are chemicals produced by one kind of tissue in an organism and then transported to other tissues in the organism, where they produce some kind of response. Because of the way they operate, hormones are sometimes called "chemical messengers." Hormones are very different from each other—depending on the functions they perform—and they occur in both plants and animals.

An example of hormone action is the chemical known as vasopressin. Vasopressin is produced in the pituitary gland (at the base of the brain) of animals and then excreted into the bloodstream. The hormone travels to the kidneys, where it causes an increase in water retention. Greater water retention...