Hormones are intrinsic chemical messengers that act within the organism. All multicellular organisms produce hormones. They are proteins, peptides, or lipids that are released by a gland in the body to affect cells/tissues/organs in other parts of the body.

The body’s endocrine system is composed of many endocrine glands, all of which secrete hormones directly into the blood. The hormones then target a specific receptor to elicit a specific response. The major endocrine glands are as follows: pituitary, pineal, thymus, thyroid, adrenal, and pancreatic. Over- or under-production of hormones by any of these glands can cause profound disease conditions.
Hormones affect metabolism, growth, homeostasis, the immune system, autonomic response, mood, sexual arousal, reproduction, hunger, and programmed cell death. Drug interference with the normal synthesis, secretion, transport, or binding of natural hormones in the body can change those hormones’ actions. Sigma-Aldrich offers a large selection of products to research the signal transduction pathways involved in the aforementioned physiological processes.