Introduction to excretion

• what is excretion?

  the removal of metabolic waste from the body
• what is metabolic waste?

  • substances that may be toxic and are produced in excess by reactions inside cells
• how are faeces removed?

  elimination
• what are the main substances excreted from the body?

  • carbon dioxide from respiration
  • nitrogen-containing compounds produced by the liver
  • bile pigments
• how is carbon dioxide excreted?

  • produced in body cells during respiration
  • transported in blood plasma (mainly as hydrogencarbonate ions)
  • excreted in lungs through exhaling
• what happens when there is an increase in carbon dioxide levels in the body?

  • there is a drop in blood pH detected by chemoreceptors in aortic arch
  • medulla stimulates increased breathing rate to remove CO2 faster
  • blood CO2 levels fall, pH of blood returns to normal