Urea and Uric Acid Cheat Sheet by ThereamDream

Uric acid is a product of the metabolic breakdown of purine bases with the formula C5H4N4O3. It forms ions and salts known as urates and acid urates.

In the liver, purines are metabo­lized into hypoxa­nthine, then to xanthine, and finally converted into uric acid by the enzyme xanthine oxidase. Once formed, uric acid is transp­orted to the kidney and it is a normal component of urine.

Amino acids can be oxidized by the body as an altern­ative source of energy. Conversion of amino acids into metabolic waste in the liver produces ammonia (NH3). If allowed to accumu­late, it would raise the pH in cells to toxic levels. Therefore, many organisms convert ammonia to urea, even though this synthesis has a net energy cost. Urea, is an organic compound with chemical formula CO(NH2)2. Being practi­cally neutral and highly soluble in water, urea is a safe vehicle for the body to transport and excrete excess nitrogen.

Urea also plays a role in the exchange system of the nephrons. Urea is reabsorbed in the inner medullary collecting ducts, thus raising the osmolarity in the medullary inters­titium, which makes the thin descending limb of the loop of Henle reabsorb water.

The blood urea nitrogen (BUN) is a measure of the amount of nitrogen in the blood that comes from urea. It is used as a marker of renal function, though it is inferior to other markers such as creatinine because blood urea levels are influenced by other factors such as diet, dehydr­ation, and liver function.