Counter-current flow

• what is counter-current flow?

  blood and water flow in opposite directions at the gill lamellae, maintaining the concentration gradient and, therefore, oxygen diffusion into the blood, along the entire length
• how does counter-flow work in bony fish?

  • water moves from the mouth cavity to the opercular cavity and into the gill pouches, where it flows between the gill lamellae
  • the blood in the gill capillaries flows in the opposite direction to the water over the gill surface
• at what point along the gill lamellae does the water have a higher oxygen concentration than the blood and what does this mean?

  at every point of the gill lamellae, the water has a higher oxygen concentration than the blood so oxygen diffuses into the blood along the whole length of the gill lamellae - this is a more efficient system than the parallel flow of the cartilaginous fish
• which type of flow in fish is more efficient?

  counter-current flow is more efficient than parallel flow
• how much oxygen do the gills of a bony fish remove from water?

  the gills of a bony fish remove about 80% of the oxygen from the water
• why is the gills of a bony fish removing about 80% of oxygen from the water important?

  this high level of extraction is important to fish, as water contains much less oxygen than air
• what does this graph show?

  it shows blood and water travelling in opposite directions - with increased distance along the lamella, the concentration of oxygen in the blood goes up and that of water goes down, until the concentration in the blood is very high and the concentration in water is very low