After the liver processes metabolites to produce urea and other byproducts, these travel with the blood to the heart, then they are oxygenated, and some of it travels through the renal artery to the kidneys.

Urea in water can decompose into ammonia which is toxic , as mentioned in a [textbook][1] page no 170 (6) , under production of ammonia.

Reactant and product are at equilibrium ,Also a gaseous product , CO2 is present which could potentially escape during oxygenation of blood , hence according to Le Chatelier's principle , equilibrium shift towards reactant is possible

NH2CONH2 + 2H2O → (NH4 )2CO3 ⇌ 2NH3 + H2O + CO2

The chance of urea decomposing into ammonia is high while travelling in the blood (i.e taking long route) and in the bladder, but it still does not happen. Why not?


  [1]: http://ncert.nic.in/ncerts/l/lech107.pdf