What is a hormone?

Humans, animals, and even plants synthesize various types of hormones. In the human body, hormones are produced by cells known as endocrine cells, which sometimes group together to form glands (mammary glands, adrenal glands, ovaries, testicles, etc.). Once produced, hormones are secreted into the blood and travel to their target organ, where they bind to specific membrane receptors. Hormones act like keys that unlock a lock. This complementarity between the hormone and its receptor triggers a cascade of chemical reactions within the cell that results in a physiological response. Thus, hormones can instruct the cell to multiply, synthesize a protein, and even self-destruct. The sum of these small cellular responses is visible at the body level, contributing to the psychological and physiological balance of the organism. For example, the growth hormone, synthesized in the brain, will bind to bone cells to stimulate the production of bone matter: this is how we grow. A hormone can even act at very low doses.