ventilation & gas exchange

• gas exchange:

  • short diffusion pathway
  • large surface area
  • large concentration gradient
  • moist walls
  • thin walls
  • permeable to gases involved
• Gas exchange in bony fish:

  • single circulatory
  • e.g trout, salmon and cod
  • large and very active = high oxygen requirement
  • Water travels in through the mouth and out through the operculum
  • one direction travel
  • gills supported by gill bar (made of cartilage)
  • space between gill bars are called gill splits
  • each grill has two rows of filaments (covered in lamellae)
• Gas exchange in bony fish:

  • lamellae provide a large surface area
  • lamellae membrane are thin to minimise diffusion distance
  • gills have rich blood supply to maintain steep diffusion gradients
  • the countercurrent flow of blood and water creates even steeper concentration gradients
• Countercurrent flow:

  • blood and water flow over lamellae in opposite directions
  • this mean when oxygen rich blood meets oxygen rich water, maximising diffusion of oxygen into blood
  • oxygen poor blood from body tissues meets oxygen reduced water still allowing diffusion
  • maintains concentration gradient
• Ventilation in bony fish:

  1. mouth opens and operculum closes
  2. buccal floor lowers so the buccal cavity volume increases. As volume increases, pressure decreases and water flows in
  3. mouth closes
  4. buccal floor raises so pressure increases
  5. operculum opens so the water is pushed out through the gills
• Gas exchange in insects:

  very active = high oxygen requirement

  tough exoskeleton through which little gas exchange can take place

  system adapted to deliver oxygen directly to tissues
• Gas exchange in insects:

  1. air enters tracheal system through spiracles
  2. air moves into the tracheae made up of chitin which prevents it from collapsing and diffuses into the tracheoles
  3. oxygen diffuses in water in tracheal fluid and diffuses down concentration gradient into body cells
  4. carbon dioxide diffuses down concentration gradient out of the body into tracheoles
  5. air is carried back to spiracles via tracheae and released from body
• Lactic acid accumulation:

  1. lactic acid accumulation reduces the water potential in tracheal fluid at the end of the tracheoles
  2. water leaves the tracheoles via osomosis
  3. a higher surface area is exposed for gaseous exchange
• Three main parts of an insect:

  • head
  • thorax
  • abdomen
• gills:

  • covered by an operculum flap
  • consist of stacked filaments containing lamellae
  • lamellae surrounded by extensive blood vessels
• tracheae

  • reinforced with spiracles of chitin - prevents from collapsing
  • multiple tracheae - increase surface area
• tracheoles

  • penetrate directly into tissues - decrease gaseous exchange distance
  • thin walls - decrease gaseous exchange distance
  • highly branched - maximise surface area
  • not reinforced with chitin - allows gaseous exchange to occur
  • tracheal fluid - allows oxygen to dissolve to aid diffusion
• spiracles

  • open and close - allows them to control gaseous exchange and minimise water loss
  • this is controlled by spiracle sphincters