Gas exchange in fish

• Describe the anatomy of a fish gill.

  • The gills are made up of stacks of gill filaments
  • Each gill filament is covered in gill lamellae, positioned at right angles to the filament.
• How does the fish gas exchange surface provide a large surface area?

  • Many gill filaments covered in many gill lamellae are positioned at right angles
  • creates a large surface area for efficient diffusion
• What is countercurrent flow?

  • When water flows over gills in opposite direction to flow of blood in capillaries
  • equilibrium not reached
  • diffusion gradient maintained across entire length of gill lamellae
• Where does gas exchange in fish occur?

  At the lamella in the gills.
• How is a short diffusion distance achieved in the fish gas exchange system?

  There is a short diffusion distance due to a capillary network in every lamella and all gill lamellae are very thin.
• How is the concentration gradient for oxygen maintained?

  By countercurrent flow
• How does countercurrent flow maintain the oxygen diffusion gradient?

  Countercurrent flow ensures that equilibrium is not reached. This ensures that a diffusion gradient for oxygen is maintained across the entire length of the gill lamellae.
• How is the fish gas exchange system adapted for efficient gas exchange?

  A large number of fish gill filaments and lamellae provide a large surface area, and the network of capillaries within each lamella ensures a short diffusion distance. The countercurrent flow mechanism maintains the diffusion gradient across the entire lamellae by ensuring that no equilibrium is reached.