Which statement best describes the relationship between ammonia and urea in blood detoxification?

Which statement best describes the relationship between ammonia and urea in blood detoxification?

• A. Ammonia is converted to urea for detoxification
• B. Urea is converted to ammonia for detoxification
• C. Ammonia is excreted as is in bile
• D. Ammonia is excreted as is in stool

Answer: (A)

Ammonia is converted to urea in the liver as the main way the body detoxifies this highly toxic byproduct of protein breakdown. In the urea cycle, ammonia from amino acid metabolism is incorporated to form urea, which is much less toxic and water-soluble. Urea then travels in the blood to the kidneys and is excreted in urine, removing the nitrogen safely from the body. This is why the statement that best describes the relationship is that ammonia is converted to urea for detoxification. The alternative ideas—that urea becomes ammonia, or that ammonia is excreted unchanged in bile or stool—do not reflect how the body handles nitrogenous waste. A small amount of ammonia can reach the gut and be metabolized by bacteria, but the primary detoxification step is conversion to urea before excretion.

Ammonia is converted to urea in the liver as the main way the body detoxifies this highly toxic byproduct of protein breakdown. In the urea cycle, ammonia from amino acid metabolism is incorporated to form urea, which is much less toxic and water-soluble. Urea then travels in the blood to the kidneys and is excreted in urine, removing the nitrogen safely from the body.

This is why the statement that best describes the relationship is that ammonia is converted to urea for detoxification. The alternative ideas—that urea becomes ammonia, or that ammonia is excreted unchanged in bile or stool—do not reflect how the body handles nitrogenous waste. A small amount of ammonia can reach the gut and be metabolized by bacteria, but the primary detoxification step is conversion to urea before excretion.