Homeostasis in humans - AQAMaintaining nitrogen balance in the body - Higher

The digestion of proteins from the diet results in excess amino acids, which need to be excreted safely. In the liver these amino acids are deaminated to form ammonia. Ammonia is toxic and so it is immediately converted to urea for safe excretion.

Once we have eaten our food, it is then digested by the body. The digestion of proteins is broken down by protease enzymes into amino acids in the stomach and small intestine.

When excessive amounts of protein are eaten, the excess amino acids produced from digesting proteins are transported to the liver from the small intestine. The liver controls the amino acid concentration in the body, as excess amino acids which need to be excreted safely. The body is unable to store proteins or amino acids.

In the liver ammonia is formed by the deamination of amino acids. It is highly toxic and cannot be allowed to accumulate in the body. Excess ammonia is converted to urea. Urea and water are released from the liver cells in to the bloodstream and transported to the kidneys where the blood is filtered and the urea is passed out of the body in the urine.