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"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.
參考答案:荷尔蒙这个词同时作为北约称呼苏联的Ka-25军用直升飞机的称谓。荷尔蒙激素（在希腊文里的意思是“正在进行中”）是一种联系细胞间的使者。所有的多细胞机体都产生荷尔蒙激素（包括随付的植物激素）。
为人所知的激素就是有脊椎动物的内分泌腺分泌的激素了，然而荷尔蒙激素在动物的任何器官系统和组织类型里都分泌着。荷尔蒙激素直接被释放到血液里；而一些被称之为外激素的荷尔蒙激素并不是被释放到血液里，而是通过循环或是被扩散到他们的目标细胞里，这些细胞在相同的组织里或是在体内的远距离的器官内。荷尔蒙的作用就是做为与目标细胞联系的信号。荷尔蒙的分泌由分泌类型以及接受信号的组织转换的信号来决定的。
大部分的荷尔蒙和与之联系的细胞由他们的受体改变着。很多蛋白质的荷尔蒙激素，他们的受体被植在细胞的表层。而荷尔蒙激素和他们的受体发生的交互作用将引起一系列的与细胞质的二次反应。通常引起蛋白质的磷酸化和脱磷作用，这一系列的离子通道的改变，或是引起细胞内的分子数目的增加，而这些分子充当起第二信使的角色。第二个普遍的机制，通常和小体形的激素，象类固醇或甲状腺激素，当他们进入细胞的细胞质的时候，在那里他们和一个松散的受体结合，而这个结合的荷尔蒙受体的配合基就穿透核膜，进入到细胞的核子部分与DNA结合了，有效地加强了或是抑制了某些基因的活动，也因此影响了蛋白质的合成。
荷尔蒙的影响是非常广泛的，这其中包括刺激或抑制成长，程序胞区的死亡，以及免疫系统的调节，同时调节着新陈代谢的功能，并且为新的活动做好准备（象打架，逃跑，交配）或者调节着生活的一段时间（象青春期，怀孕期，和绝经期）。许多例子表明，一种荷尔蒙可能调节或释放着其他的荷尔蒙。许多对荷尔蒙的信号的反应被描述为为器官或组织的代谢活动来服务的。事实上，荷尔蒙同样调节着多细胞机体的再生循环。
P.S. 这是我自己翻的，有不到之处，还请见谅。
