The effects of estradiol-3, 17b on embryonic hamster kidney cells in vitro

Animals and plants possessing organs are distinguished from other cellular forms of life in having their biochemical processes regulated by hormonal control mechanisms, in addition to the fundamental principles of regulation within the cell itself. Hormones of animals, often called distance activators, are chemical substances made by the endocrine glands and secreted into the blood stream. These compounds are then carried by the blood and lymph to all parts of the body, where they modify the activity of specific genetically conditioned target organs by an intricate feedback mechanism, as illustrated below (Nalbandov, 1964)