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Organisation (Enzymes in digestion (Bile (Neutralises the stomach acid and…

- - - - Pancreas
      - Small intestine
      - Salivary glands
  - - - Pancreas
      - Small intestine
      - Stomach (pepsin)
  - - - Pancreas
      - Small intestine
- - - - Very good blood supply
      - Huge surface area for efficient gas exchange
      - Moist thin walls (one cell thick) to increase diffusion rate
- - - - A group of cells in the right atrium control the resting heart rate - act as a pacemaker
      - These cells produce a small electric impulse which causes the surrounding muscle cells to contract
  - - - Strong and elastic to cope with the blood being under high pressure
      - Thick walls with small lumen (the hole through which the blood flows)
      - Thick layers of muscle to make them strong, and elastic fibres to allow the to pump the blood by contracting
      - Carry oxygenated blood
    - - Arteries branch into capillaries
      - One cell thick to allow quick and efficient gas exchange as distance through which gases have to diffuse is decreased
      - Permeable walls so substances can diffuse in out out
      - Supply nutrients and oxygen, and take away CO2
    - - Capillaries join together to form veins
      - Carry deoxygenated blood
      - Blood is at low pressure - thin walls needed
      - Bigger lumen than arteries (large and saggy) to help the blood flow
      - Contain valves to make sure the blood flows in the right direction
  - - - Carry oxygen from the lungs to cells in the body
      - Large, flat bioconcave disk shape to increase surface area for absorbing oxygen
      - Doesn't contain a nucleus to give more space to haemoglobin, which is a red pigment
      - Haemoglobin binds to oxygen in the lungs to form oxyhaemoglobin, and then splits to form oxygen and haemoglobin, to allow the oxygen to be released into the cells
    - - Bodies way of defending against infection
      - Not alive - made of specialised proteins, and do contain a nucleus
    - - Help with blood clotting to stop excessive blood loss and to stop pathogens entering the body
      - Small fragments of cells with no nucleus
      - Lack of platelets can cause excessive bleeding and bruising
    - - Pale, straw coloured liquid that carries:
        
        Red and white blood cells
        
        Platelets
        
        Nutrients such as glucose and amino acids - products of digestion
        
        CO2 from organs to lungs
        
        Urea (toxic) from the liver to the kidneys
        
        Hormones
        
        Proteins
        
        Antibodies and antitoxins produced by the WBCs