features of a specialised exchange surface (lungs)

• features of a specialised exchange surface:

  • large surface area
  • moistened surface
  • thin and freely permeable
  • with a transport system
  • concentration gradient
• nasal cavity

  • good blood supply - warms the air
  • hairy lining - traps dirt and bacteria
  • moist surfaces - increases humidity of air and reduces evaporation from the exchange surfaces
• trachea (windpipe)

  • divides into 2 bronchi
  • 16 - 20 C shaped cartilage rings joined by connective tissue - supports the trachea from collapsing and allows food to pass down the oesophagus
  • smooth muscle and elastic fibres allows the lumen to constrict and relax
  • contains ciliated epithelium and goblet cells - mucus is secreted and wafted to the airways - prevents substances entering the lungs
• bronchus

  • trachea branches into left and right brochus
  • similar structure to trachea but smaller
  • left bronchus is primary
• bronchioles

  • each bronchi divides approx 23 times
  • 1mm thick
  • no cartilage
  • walls contain smooth muscle - contract and relax to alter the amount of air reaching the lungs
  • lined with thin layer of flattened epithelium cells - some gas exchange is possible
• alveoli

  • 3 million alveoli
  • contain elastic fibres, flattened epithelial cells and collagen - elastic fibres cause recoil to help move the air out
  • 200 to 300 um in diameter
  • large surface area - 1500 sq ft
  • good blood supply - 280 million capillaries - steep concentration gradient
  • surfactant stops them from sticking together - decreases surface tension
• pleural cavity

  • each lung is enclosed by a double membrane - pleural membrane
  • between the 2 membranes is the pleural cavity - filled with pleural fluid
  • pleural fluid lubricates the lungs and adheres to the chest cavity - so that the lungs can expand with the chest whilst breathing