Excretory System

• Excretory system


  Regulates the chemical composition of body fluids by removing metabolic wastes and retaining the proper amounts of water, salts and nutrients
• Components of the excretory system

  • Kidneys
  • Liver
  • Lungs
  • Skin
• Excretion


  Removal of metabolic waste from the body
• By-products of metabolism are often toxic and need to be removed before reaching dangerous concentrations
• Excretory organs


  • Lungs - carbon dioxide
  • Liver - processes substances so they can be excreted
  • Sweat glands - contains by products of metabolism
  • Alimentary canal - passes out bile pigments
  • Kidney - principle excretory organ
• Skin


  • Sweat glands located in lower layers
  • Ducts carry sweat to a pore at the skin's surface
  • Cells surrounding the glands contract and squeeze the sweat
  • Sweat contains water with dissolved salts, urea, lactic acid and some drugs
  • Sweat glands secrete about 500ml of water/day
• Liver


  • Prepares material for excretion
  • Protein is rarely used for energy releasing reactions
  • Excess protein from diet cannot be stored must be processed for removal
• Protein breakdown


  1. Some protein is normally broken down into amino acids

  2. Some amino acids are used to make new proteins

  3. Small amounts of amino acids are lost in urine, skin, hair and fingernails
• Using proteins as an energy source

  1. Amino group (NH2) must be removed from the amino acids

  2. This process is called deamination

  3. Deamination occurs in the liver through enzyme action

  4. Amino group is converted into ammonia then urea

  5. Urea is eliminated in the urine

  6. Remaining molecule is largely carbon and hydrogen

  7. This is converted to carbohydrate

  8. Carbohydrate can then undergo cellular respiration for energy
• Ammonia


  • Highly toxic to cells and soluble in water
  • Liver rapidly converts ammonia to less toxic urea
  • Urea is easily excreted by kidneys, a little in sweat and eliminated in urine
• Other liver functions


  • Detoxifies alcohol and other drugs
  • Deactivates hormones for excretion
  • Breaks down haemoglobin from RBCs to produce bile pigments which are eliminated in faeces
• Organs involved in excretion

  • Lungs - carbon dioxide
  • Liver - processes substances so they can be excreted
  • Sweat glands - contains by products of metabolism
  • Alimentary canal - passes out bile pigments
  • Kidney - principle excretory organ
• Alimentary canal's role in excretion

  1. Long tube from oesophagus to anus

  2. Anus and rectum is where majority of wastes are excreted through faeces

  3. Also passes out bile products
• Breaking down and removing amino acids from the body

  1. In the liver, deamination occurs where enzymes act on amino acids converting the amino group into ammonia

  2. Ammonia is then converted into urea which is eliminated in the urine
• People can remain healthy with one kidney as they can still function normally
• Living donors can donate a lobe/portion of an organ to a recipient due to size differences in anatomy
• Excess alcohol consumption


  Higher risk of liver problems
• The liver is responsible for detoxing alcohol but if there is too severe a quantity for the liver to handle, the alcohol can be toxic within the body and cause harm to tissues