by 
Spixxy
ANSWERS: 2
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Uric acid is the end product of purine metabolism (purines are building blocks of RNA and DNA). Most uric acid produced in the body is excreted by the kidneys. An overproduction of uric acid occurs when there is excessive breakdown of cells, which contain purines, or an inability of the kidneys to excrete uric acid. It is a white odorless, tasteless, and nearly insoluble acid that is the chief nitrogenous waste present in the urine especially of lower vertebrates (as birds and reptiles), is present in small quantity in human urine. Greater-than-normal levels of uric acid in humans may indicate: acidosis alcoholism diabetes gout hypoparathyroidism lead poisoning leukemia nephrolithiasis polycythemia vera renal failure toxemia of pregnancy purine-rich diet severe exercise Lower-than-normal levels of uric acid in humans may indicate: Fanconi's syndrome Wilson's disease SIADH low purine diet
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While high levels of uric acid are abnormal in human urine (we use urea, a water-soluble compound, to get rid of our nitrogenous waste), there are plenty of animals that use water-insoluble uric acid as their main nitrogenous waste, and it's not just because they're "lower" animals (man, I hate that term). The evolutionary reason is basically water conservation. If you're looking to conserve water, as many land animals (some insects, birds, reptiles, and even some mammals) are, one great way to do it is by reducing the amount of water you require to flush out your nitrogenous waste. uric acid does this nicely, because it turns into a sort of pasty white goop which requires a LOT less water to flush out of an animal's system than an equal amount of urea. In bird poop (which is actually poop AND pee), the white stuff is the uric acid, while the chunky brown stuff is the actual poop.
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