英语翻译From Wikipedia,the free encyclopedia Jump to:navigation,

英语翻译From Wikipedia,the free encyclopedia Jump to:navigation,search "Hormone" is also the NATO reporting name for the Soviet/Russian Kamov Ka-25 military helicopter.A hormone (from Greek ορμή - "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).The best-known animal hormones are those produced by endocrine glands of vertebrate animals,but hormones are produced by nearly every organ system and tissue type in an animal body.Hormone molecules are secreted (released) directly into the bloodstream; some hormones,called ectohormones,are not secreted into the blood stream,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.Most hormones signal a cell change by combining with a receptor.For many hormones,including most protein hormones,the receptor is embedded in the membrane on the surface of the cell.The interaction of the hormone and the receptor typically triggers a cascade of secondary effects within the cytoplasm of the cell,often involving phosphorylation or dephosphorylation of proteins,changes in ion channels,or increased amounts of an intracellular molecule that serves as a second messenger (e.g.,cyclic AMP).The second common type of mechanism,typically involving smaller-sized hormones such as steroid or thyroid hormones,begins with entry of the hormone molecule into the cytoplasm of the cell where it combines with a loose and mobile receptor.The combined hormone-receptor ligand then moves across the nuclear membrane into the nucleus of the cell and binds to the DNA,effectively amplifying or suppressing the action of certain genes,thereby affecting protein synthesis.Hormone effects 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.