Excretion

• Excretion

  • Toxic metabolic waste products’ removal
  • Main Waste:
  • CO_2 from decarboxylation in respiration
  • Nitrogen-containing products, e.g. ammonia, uric acid, creatine and urea
  • Organs:
  • Lungs (remove CO_2)
  • Liver (detoxify; produce urea from excess amino acids)
  • Kidney (filter urea from blood; form urine)
• Excess CO_2 or amino acids in blood

  Amino Acid

  • Cannot be stored
  • Amino group removed from each form ammonia
  • Toxic + soluble
  • Form alkaline solution
  • Increasing pH; change proteins' tertiary structure
  • Rapidly converted to urea in liver; still toxic but less soluble

  CO_2

  • Combines with water to form carbonic acid
  • Dissociates to form hydrogen and hydrogen carbonate ions (catalysed by carbonic anhydrase)
  • If pH lowers below 7.35
  • Respiratory acidosis (acid blood)
  • Slowed breathing, drowsiness, headache and confusion
  • Reduces haemoglobins’ oxygen affinity
  • Hydrogen competes with oxygen