Hormone

A hormone (from Greek horman - "to set in motion") is a chemical messenger from one cell (or group of cells) to another. All multicellular organisms produce hormones (including plants - see article phytohormone).

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The best known animal (and human) hormones are those produced by endocrine glands of vertebrate animals, but hormones are produced by nearly every organ system and tissue type in a human or animal body. Hormone molecules are secreted (released) directly into the bloodstream, other body fluids, or into adjacent tissues. They move by circulation or diffusion to their target cells, which may be nearby cells (paracrine action) in the same tissue or cells of a distant organ of the body. The function of hormones is to serve as a signal to the target cells; the action of hormones is determined by the pattern of secretion and the signal transduction of the receiving tissue.

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Hormone actions vary widely, but can include stimulation or inhibition of growth, induction or suppression of apoptosis (programmed cell death), activation or inhibition of the immune system, regulating metabolism and preparation for a new activity (e.g. fighting, fleeing, mating) or phase of life (e.g. puberty, caring for offspring, menopause). In many cases, one hormone may regulate the production and release of other hormones. Many of the responses to hormone signals can be described as serving to regulate metabolic activity of an organ or tissue. Hormones also control the reproductive cycle of virtually all multicellular organisms.

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Greek: The noun Greek refers to:...

Chemical: REDIRECT Chemical substance...

Cell: A cell is a single unit or compartment, enclosed by a border or wall. A cell is usually part of a larger structure. More specific meanings depend on the context in which the work is used....