The Role of the Liver in Excretion | Biology for GCSE/IGCSE - Year 11 PDF Download

Excretion by Deamination of Amino Acids

• Many digested food molecules from the small intestine are transported to the liver for assimilation.
• Assimilation: This process involves converting food molecules into essential compounds needed by the body.
• Among these molecules are amino acids, which play a crucial role in building proteins like fibrinogen found in blood plasma, vital for blood clotting.
• Fibrinogen: A key protein in blood plasma necessary for clot formation.
• Excess amino acids that are not utilized for protein synthesis cannot be stored and undergo deamination.
• Excess amino acids: Additional amino acids beyond what is required for protein formation.
• Deamination: The process of breaking down amino acids by removing their amino group (NH₂).
  • The amino group (NH₂) containing nitrogen is eliminated, leading to deamination.
  • Amin(o): The term relates to the removal of the amino group in amino acids.
• Enzymes in the liver facilitate the breakdown of amino acid molecules.
• The carbon-containing portion of these molecules is converted into glycogen for storage.
• Carbon: Part of the amino acid molecule utilized in glycogen formation.
• Glycogen: A storage form of glucose in the body.
• The nitrogen-containing segment is transformed into toxic ammonia, swiftly converted into urea for reduced toxicity.
• Nitrogen: Component of amino acids converted to ammonia during the deamination process.
• Ammonia: Highly toxic byproduct converted into urea for safer excretion.
• Urea dissolves in the blood, transported to the kidneys for excretion, with a minor amount eliminated through sweat.
• Kidney: Organ responsible for filtering and excreting waste products like urea.
• Sweat: Small quantities of urea are also expelled from the body through sweat.

• During deamination, the nitrogen-containing amino group is separated and transformed into ammonia, subsequently converted into urea for excretion.
• The toxic consequences of high urea levels, if it is not excreted effectively, are very serious:
  • Cell death
  • Reduced response to insulin, leading to diabetes
  • Deposits inside blood vessels