What is a hormone?

Humans, animals, and even plants synthesise various types of hormones. In the human body, hormones are produced by cells known as endocrines, 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 attach 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, leading to a physiological response. Thus, hormones can instruct the cell to multiply, synthesise 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, synthesised in the brain, will attach to bone cells to stimulate the production of bone matter: this is how we grow. A hormone can even act at a very low dose.