What is the purpose of the urea cycle?

• A. Detoxification of ammonia by converting it to urea for excretion
• B. Synthesis of urea in the kidneys
• C. Breakdown of urea to ammonia
• D. Regulation of glucose metabolism

Answer: (A)

The urea cycle exists to detoxify ammonia produced when proteins are broken down. Ammonia is highly toxic, especially to the brain, so the liver converts it into urea, a much less toxic, water-soluble compound. This urea is then transported in the blood to the kidneys, where it is excreted in urine. This whole process is why you hear it called the ornithine cycle and why the liver, not the kidneys, carries out the cycle.

So the purpose is to safely transform toxic ammonia into excretable urea. It isn’t about making urea in the kidneys, breaking urea back into ammonia, or regulating glucose metabolism.