Lecture Notes: Gas Exchange in Fish

Introduction

• Focus on gas exchange in fish.
• Fish are waterproof due to scales and have a small surface area to volume ratio.
• Require gills as the gas exchange surface.
• Water contains 30 times less oxygen than air.
• Adaptation needed to maintain concentration gradients.

Key Features of Gas Exchange Surfaces

• Large Surface Area to Volume Ratio
• Short Diffusion Distance
• Mechanism to Maintain Concentration Gradients

Fish Gills Structure

• Four layers of gills on both sides of the head.
• Gill Filaments: Long parts aligning in stacks.
• Gill Lamellae: Thin structures positioned at right angles to filaments.
  • Create a large surface area.
  • Diffusion occurs on the lamellae.

Gas Exchange Features in Fish

• **Large Surface Area: **
  • Many gill filaments covered in numerous gill lamellae.
• Short Diffusion Distance:
  • Gas exchange happens only on thin gill lamellae.
  • Capillary network close to the surface aids short diffusion.
• Maintaining Concentration Gradient:
  • Counter current flow ensures continuous diffusion.

Counter Current Flow Explained

• Counter Current Flow: Water flows opposite to blood in capillaries.
  • Prevents equilibrium – diffusion occurs across entire lamellae.
• Concurrent Flow (Contrast):
  • Water and blood flow in the same direction.
  • Risk of reaching equilibrium quickly, limiting diffusion.

Advantages of Counter Current Flow

• Maintains diffusion gradient along the entire length of the lamellae.
• Key Exam Points:
  • Equilibrium is not reached.
  • Water flows opposite to blood.
  • Gradient maintained across the entire lamellae, not just part.

Conclusion

• Reviewed fish gas exchange systems.
• Importance of surface area, short diffusion distance, and concentration gradients.

• Tip: Mention counter current flow and its advantages in exams.

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