| Urea is the end product of protein metabolism in mammals, and excretion is therefore called ureotelic. |
| Guanidino compounds in serum, urine, liver, kidney, and brain of man and some ureotelic animals. |
| Like most other land animals, mammals are ureotelic, and convert ammonia into urea, which is done by the liver as part of the urea cycle. |
| The classification of animals as amoniotelic, ureotelic, and uricotelic is based exclusively on the predominance of nitrogenated metabolic compounds in excreta. |
