Fish

• Fish have gills with projections called lamellae that provide a large surface area for gas exchange.
• Gills have a good blood supply, which maintains a steep diffusion gradient across the exchange surface.
• A countercurrent mechanism in fish, in which the directions of blood flow and water flow are opposite to one another, ensures that a diffusion gradient is maintained along the whole length of the exchange surface.
• Gas exchange occurs through simple diffusion as the gill filament is covered in thin-walled epithelial tissue called gill lamellae. These are supported on a framework of cartilage or bone.
• The gills of fish are highly adapted structures for extracting oxygen from water. The gill filaments contain many small blood capillaries arranged parallel to the surface of the gill lamellae. This increases the surface area available for gas exchange.
• Oxygen dissolves less readily in water. A given volume of air contains 30 times more oxygen than the same volume of water.
• Fish are adapted to directly extract oxygen from water.
• 𝙎𝙏𝙍𝙐𝘾𝙏𝙐𝙍𝙀 𝙊𝙁 𝙁𝙄𝙎𝙃 𝙂𝙄𝙇𝙇𝙎:

  • Series of gills on each side of the head
  • Each gill arch is attached to two stacks of filaments
  • On the surface of each filament, there are rows of lamellae
  • The lamellae surface consists of a single layer of flattened cells that cover a vast network of capillaries
• 𝘾𝙊𝙐𝙉𝙏𝙀𝙍𝘾𝙐𝙍𝙍𝙀𝙉𝙏 𝙈𝙀𝘾𝙃𝘼𝙉𝙄𝙎𝙈 𝙄𝙉 𝙁𝙄𝙎𝙃:

  • The capillary system within the lamellae ensures that the blood flow is in the opposite direction to the flow of water - it is a countercurrent system
  • The countercurrent system ensures the concentration gradient is maintained along the whole length of the capillary
  • The water with the lowest oxygen concentration is found adjacent to the most deoxygenated blood
• Structure of Fish Gills:

  A) Arch

  B) Blood

  C) Lamellae

  D) Filaments

  
• The Countercurrent Mechanism in Fish:

  A) Lamellae

  B) Oxygen

  C) Opposite

  D) Lower

  E) Deoxygenated

  F) Oxygenated

  
• 𝙑𝙀𝙉𝙏𝙄𝙇𝘼𝙏𝙄𝙊𝙉 𝙄𝙉 𝙁𝙄𝙎𝙃:

  The ventilation mechanism in fish constantly pushes water over the surface of the gills and ensures they are constantly supplied with water rich in oxygen (maintaining the concentration gradient).