exchange surfaces and breathing

• the need for specialised exchange surfaces

  • distances are too great to travel
  • oxygen demands are high
  • small SA:V
• features of effective exchange surfaces

  • ventilation
  • increased surface area
  • thin layers
  • good blood supply
• peak flow meter

  • rate which air can be expelled from the lungs
• vitalographs

  • produces a graph showing amount and how quickly air is breathed out
• spirometer

  • measures different aspects of lung volume
• tidal volume

  • volume of air that moves into and out of the lungs per breath
• vital capacity

  • volume of air breathed in when the strongest possible exhalation is followed by deepest possible intake of breath
• inspiratory reserve volume

  • volume of air forcibly inspired after a normal breath
• expiratory reserve volume

  • volume of air forcibly expired after a normal breath
• residual volume

  • volume of air that remains in the lungs after maximal expiration
• ventilation= tidal volume x breathing rate
• inspiration

  1. diaphram contracts
  2. external intercoastal muscles contract
  3. pressure in the thorax decreases
  4. air is drawn in
• expiration

  1. diaphram relaxes
  2. external intercoastal muscles relax
  3. pressure in the thorax increases
  4. air moves out of lungs until pressure is equal
• ventilation and gas exchange in insects

  1. air enters and leaves through the spiracles. they are kept closed as much as possible by sphincters
  2. when oxygen demand is high and carbon dioxide levels are high, spiracles open
  3. leading away from the spiracles are the tracheae, their tubes are lined with chitin
  4. tracheae branch into tracheoles, these run between cells to deliver the oxygen
• larger insects need mechanical ventilation

  • air is actively pumped into the system by pumping movements of the thorax
  • collapsible enlarged air sacs increase amount of air moved in. inflated/ deflated by throax
• the tips of adjacent gill filaments overlap

  • increases resistance
  • movement of water slows down
  • more time for gas exchange
• ventilation in fish

  1. the mouth is opened, increasing volume of buccal cavity
  2. pressure in the cavity drops, water moves into the cavity
  3. opercular valve shuts and opercular cavity containing gill expands, lowering pressure
  4. pressure in buccal cavity increases causing water to move over gills
  5. the mouth closes and opercular opens
  6. pressure in the opercular cavity increases and water is forced over the gills and out the operculum
  7. buccal cavity moved up to maintain a flow of water over the gills
• countercurrent

  • blood and water flow in opposite directions so an oxygen concentration gradient between water and blood is maintained along the gill
  • oxygen continuous to diffuse down the concentration gradient
  • higher levels of oxygen saturation in the blood is achieved