Mammals make urea in the [A] Liver. Urea synthesis primarily occurs in the liver as a result of the deamination of amino acids during protein metabolism. The liver contains enzymes necessary for this process, converting ammonia, a toxic byproduct of protein breakdown, into urea, a less toxic compound. Once synthesized, urea is released into the bloodstream and transported to the kidneys for excretion. In the kidneys, urea is filtered out of the blood and excreted in urine, contributing to the body’s waste removal process.
The spleen is primarily involved in immune function and does not play a direct role in urea synthesis. The bladder, often colloquially referred to as a “bag,” is an organ involved in urine storage and does not produce urea but rather temporarily stores urine before elimination from the body.