The Integrative Aspects of Fluid and Electrolyte Balance in Birds

9515450丹兹勒在哺乳动物中，肾脏是唯一负责调节体内水和盐含量的器官，哺乳动物有一个膀胱，将肾脏(尿液)的输出储存在其中，直到膀胱在方便和安全的时间排空。另一方面，在鸟类中，肾脏与下消化道(GI)一起发挥作用，调节身体的盐分和水分含量。这是因为鸟类没有用来储存尿液的膀胱。相反，尿液进入胃肠道的末端，即泄殖腔。尿液不会留在这里排出，而是通过泄殖腔和结肠的肌肉收缩进入胃肠道(结肠)。在结肠中，构成结肠内层的细胞可以改变尿液的成分。因此，肾脏必须与下消化道一起工作，以维持液体和盐分的平衡。如何控制这种功能整合是拟议研究的主要重点之一。更好地了解鸟类如何调节水和盐平衡对于商业目的鸟类的种植者非常重要，特别是家禽养殖业，在家禽养殖业中，家禽群中水和盐平衡的干扰相当频繁，可能会产生重大的经济影响。这项拟议工作的另一个重点涉及鸟类如何排泄作为新陈代谢副产品形成的氮。哺乳动物排出的氮以尿素的形式存在，尿素溶于水，除非有严重的肾脏损伤，否则很少会出现问题。另一方面，鸟类将多余的氮以尿酸的形式排泄出来，尿酸是一种几乎不溶于水的化合物，往往会从溶液中沉淀出来，形成大的板状晶体。然而，当检查鸟类的尿液时，尽管尿酸浓度很高，但没有发现尿酸结晶。尿液中含有的小球体不是结晶，而是足够小，可以在不拖拽肾小管的情况下沿肾小管传递。我们已经确定这些小球是由尿酸和蛋白质组成的。人们对这些尿酸小球在肾脏中形成的机制和位置知之甚少。鸟类通常不会形成肾结石，目前还不清楚为什么结石不是更普遍，因为尿液中有大量的尿酸。然而，肾结石的暴发确实发生在商业鸡群中，造成灾难性的后果。了解鸟类肾脏处理尿酸的基本过程将有助于人们更有效地处理商业鸡群和处理外来鸟类交易中肾结石的爆发。总而言之，研究结果应该有助于更好地了解鸟类的肾脏功能，以及肾脏如何与下消化道一起发挥作用，以维持整个动物的水和盐平衡。

9515450 Dantzler In mammals the kidney is the sole organ responsible for regulating the water and salt content of the body and mammals have a urinary bladder in which to store the output of the kidneys (urine) until the bladder can be emptied at a convenient and safe time. In birds on the other hand, the kidneys function together with the lower gastrointestinal (GI) tract to regulate the salt and water content of the body. This is because birds do not have a urinary bladder in which to store urine. Instead, the urine enters the terminal portion of the GI tract, the cloaca. The urine does not remain here to be excreted, but is moved into the GI tract ( the colon) by muscular contractions of the cloaca and colon. In the colon, the composition of the urine can be modified by the cells that make up the lining of the colon. Thus, the kidney must work together with the lower GI tract to maintain the fluid and salt balance. How this integration of function is controlled is one of the major emphasis of the proposed research. A better understanding of how birds regulate water and salt balance is of major importance to growers of birds for commercial purposes, especially the poultry industry where quite frequently disturbances of water and salt balance in flocks can have significant economic impact. Another emphasis of the proposed work deals with how birds excrete the nitrogen that is formed as a by product of metabolism. Mammals excrete nitrogen as urea which is quite soluble in water and seldom causes problems unless there has been major kidney damage. Birds on the other hand excrete their excess nitrogen as uric acid, a compound that is virtually insoluble in water and tends to precipitate from solution and form large plate-like crystals. However, when bird urine is examined no crystals of uric acid are found despite of very high concentrations of uric acid. Instead of crystals the urine contains small spheres that are sufficiently small to pass along the kidney tubules without pl ugging the tubules. We have already determined that these small spheres are up of uric acid and protein. Very little is known by what mechanism and where in the kidney these spheres of uric acid form. Birds do not often form kidney stones, and it is not understood why stones are not more prevalent with the large amount of uric acid in the urine. However, out breaks of kidney stones do occur in commercial flocks with disastrous effects. Understanding the basic process of how bird kidneys handle uric acid will help people to deal more efficiently with out breaks of kidney stones in commercial flocks and in the trade that deals with exotic birds. In summary, the results of the studies should lead to a better understanding of kidney function in birds and how the kidneys function together with the lower GI tract to maintain whole animal water and salt balance.