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  4. Out of the following,which one is excreted in human urine?

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Q. Out of the following,which one is excreted in human urine?

NTA AbhyasNTA Abhyas 2020

Solution:

Since all mammals are ureotelic organisms, humans also excrete urea from their body through urine. This nitrogenous product is formed in the liver by two processes:
  1. Deamination: Amino acid oxidation separates amino group and give pyruvic acid as a product. Pyruvic acid enters the Krebs cycle; the amino group is converted into ammonia through the process of deamination.
  2. Ornithine cycle or Urea Cycle (Kreb-Henseleit cycle): In the liver, CO2 combines with NH3 to form carbamoyl phosphate, and H2O. Carbamoyl phosphate reacts with ornithine to form citrulline, which further combines with ammonia to give arginine. Arginine breaks into urea and ornithine in the presence of arginase and water. Ornithine re-enters the cycle.
Liver cells, thus, continuously remove ammonia and some CO2 from the blood and release urea. Kidneys continuously remove this urea from the blood and eventually excrete it through the urine.