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Excretion in our body occurs through skin, kidneys, and lungs.

The elimination of urea from an organism is termed as Ureotelism, and the animals that excrete their wastes majorly in various forms of nitrogen such as urea are called Ureotelic animals. Excretion in our body occurs through skin, kidneys, and lungs. They excrete toxic substances. Carbon dioxide is released from the lungs, the kidneys remove excess water, salts, and urea while skin eliminates salts and water from our body.

Urea is a colourless compound, crystalline in nature obtained as a result of protein digestion in the form of a nitrogenous product. It is formed when proteins produce amino acids post-digestion. These excess amino acids are broken down into ammonia and further into urea by the Liver through the urea cycle, since ammonia is more toxic than urea.

Chemically, urea consists of nitrogen, oxygen, and carbon and is usually found in blood, sweat, urine etc in our body. Nitrogen is found in more quantities than any other element in urea. The urea cycle begins with the deamination in the liver where amino acids are broken down into ammonia. Ammonia is a toxic substance, its accumulation in the body could be fatal. Molecules and enzymes present in the liver convert this toxic ammonia into urea. The cycle absorbs one carbon dioxide molecule and two ammonia molecules producing a molecule of urea one molecule of ornithine for the cycle to continue. The components of  excretion in humans  include glucose, water, salts, and urea. It is carried out by the kidneys via blood filtration at higher pressures. Blood reabsorbs water, salts, and glucose but not urea. It is eliminated from the body as a solution which constitutes the urine. The urea-cycle disorder can affect the liver’s ability to detoxify ammonia.

Detoxification of ammonia leads to the consumption of three molecules of ATP. This cycle called the ornithine-urea cycle was discovered in 1932 by Kreb and Hensleit. The cycle involves 5 chemical reactions which are catalyzed by enzymes.

Enzyme  – Carbamoyl phosphate synthetase.

Enzyme  – Ornithine Carbomoyl-transferase

Enzyme  – Argininosuccinate synthetase

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