GCSE Biology (AQA)

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Nitrogen Balance

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Homeostasis and Response Hormonal Coordination in Humans

Nitrogen Balance

2:19 Role of the Kidneys in Homeostasis
Spec 4.5.3.3
Previous Water Balance Next The Kidneys
  • Protein excretion helps the body maintain nitrogen balance.
  • Nitrogen balance is the comparison of nitrogen intake through diet versus nitrogen excretion.
  • Consuming protein increases nitrogen levels as proteins are rich in nitrogen.
  • Excess protein is broken down into urea, which is excreted in urine, reducing nitrogen levels.
  • Proteins are broken down into amino acids, which are the building blocks of proteins and have various functions in the body.
  • Unused amino acids cannot be stored and must be removed from the blood and excreted.
  • Kidneys remove amino acids from the blood.
  • Amino acids are too large to be filtered directly by the kidneys.
  • Amino acids are broken down into ammonia (toxic) and then converted into urea (non-toxic).
  • Urea, dissolved in water, can be safely stored in the body as urine or excreted through sweat.
  • Urea is small enough to be filtered from the blood into urine.
  • Not all animals produce urea; for example, birds convert ammonia into uric acid to avoid carrying excess water.
  • Amino acids are primarily broken down in the liver, which is located next to the stomach on the right side of the abdomen.
  • The process of breaking down amino acids into ammonia and then urea in the liver is known as deamination.

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