Wright P A
Department of Zoology, University of Guelph, Ontario, Canada.
J Exp Biol. 1995 Feb;198(Pt 2):273-81. doi: 10.1242/jeb.198.2.273.
There are diverse physiological functions of nitrogen end products in different animal groups, including excretion, acid-base regulation, osmoregulation and buoyancy. Animals excrete a variety of nitrogen waste products, but ammonia, urea and uric acid predominate. A major factor in determining the mode of nitrogen excretion is the availability of water in the environment. Generally, aquatic animals excrete mostly ammonia, whereas terrestrial animals excrete either urea or uric acid. Ammonia, urea and uric acid are transported across cell membranes by different mechanisms corresponding to their different chemical properties in solution. Ammonia metabolism and excretion are linked to acid-base regulation in the kidney, but the role of urea and uric acid is less clear. Both invertebrates and vertebrates use nitrogen-containing organic compounds as intracellular osmolytes. In some marine invertebrates, NH4+ is sequestered in specific compartments to increase buoyancy.
在不同动物群体中，含氮终产物具有多种生理功能，包括排泄、酸碱调节、渗透调节和浮力调节。动物会排泄多种含氮废物，但氨、尿素和尿酸占主导地位。决定氮排泄方式的一个主要因素是环境中的水分可利用性。一般来说，水生动物主要排泄氨，而陆生动物则排泄尿素或尿酸。氨、尿素和尿酸通过与其在溶液中不同化学性质相对应的不同机制跨细胞膜运输。氨的代谢和排泄与肾脏中的酸碱调节有关，但尿素和尿酸的作用尚不清楚。无脊椎动物和脊椎动物都将含氮有机化合物用作细胞内渗透剂。在一些海洋无脊椎动物中，NH4+被隔离在特定隔室中以增加浮力。
