How is ammonia detoxified in the liver and what condition results if this process fails?

• A. Ammonia is converted to urea via the urea cycle; failure can cause hyperammonemia and hepatic encephalopathy
• B. Ammonia is excreted unchanged in urine
• C. Ammonia is stored as glutamine in the liver
• D. Ammonia is converted to nitrate

Answer: (A)

Ammonia detoxification in the liver happens mainly through the urea cycle, a set of enzymes that convert toxic ammonia into urea, which the kidneys can excrete. In the liver, ammonia enters the urea cycle and is sequentially processed to form urea. If this pathway fails—due to enzyme deficiencies or severe liver damage—ammonia accumulates in the blood (hyperammonemia). The brain is particularly sensitive to ammonia, and elevated levels can cause hepatic encephalopathy, leading to confusion, sleepiness, and even coma.

Other ideas don’t fit because ammonia is not excreted unchanged in urine, ammonia isn’t stored long-term as glutamine in the liver (glutamine is formed in other tissues and plays a role in detox elsewhere), and converting ammonia to nitrate is not a human metabolic pathway.