7. Absorption of Materials

• The Lungs

  
• The alveoli is the site of gas exchange in the lungs.
• Oxygen is breathed into the lungs and is passed to the blood.
• Waste carbon dioxide is passed from the blood to the lungs where it is breathed out.
• The alveoli are specialised to assist gas exchange.
• The lining of the alveoli is very thin so that gas can quickly diffuse through it.
• Human lungs contain around 500 million alveoli. Increases the area for gas to diffuse.
• The alveoli has good blood supply. Dense capillary network so that large volumes of gas can be exchanged.
• Food digestion takes place in the intestines.
• The small intestine has specialised structure known as villi to aid absorption.
• The villus has thin walls which allows food to be absorbed quickly and easily.
• The villus have blood capillaries which provide a rich blood supply. Efficiently absorbs amino acids and glucose.
• The villus has a lacteal which absorbs the products of fat digestion - fatty acids and glycerol.
• The villus has:

  • Thin Walls
  • Blood Capillary
  • Lacteal
• The thin walls are the structure outside the villus.
• The blood capillaries are the cage-like structure covering the lacteal
• The lacteal is the structure underneath the capillaries, a long structure in a curved line.