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Review – factors needed for efficient gas exchange

Review – factors needed for efficient gas exchange. Large surface area:volume Moist surface to dissolve gases Thin membranes for a short diffusion path Concentration gradient is maintained. Gas Exchange in Fish. Fish have internal gills over which water continually flows.

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Review – factors needed for efficient gas exchange

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  1. Review – factors needed for efficient gas exchange • Large surface area:volume • Moist surface to dissolve gases • Thin membranes for a short diffusion path • Concentration gradient is maintained

  2. Gas Exchange in Fish • Fish have internal gills over which water continually flows. • The water has oxygen dissolved in it. • Bony fish have a ventilation mechanism. • Cartilaginous fish need to continuously move, or sit in flowing water.

  3. Fish Anatomy Mouth (Buccal Cavity) Operculum Buccal Floor

  4. Behind the Operculum… …lie the gills – the fish’s equivalent of our lungs

  5. Gill Structure • Gill rakers • Gill arches/bars • Gill filaments • Lamellae

  6. Structure of Gills • The gills are made of numerous thin filaments supported by a bony arch.

  7. Adaptations of the gills for efficient gas exchange – which features? • Large surface area : volume • allows more diffusion of gases • Permeable membranes • allows gases to diffuse through tissues • Thin (flattened cells) • short diffusion distance • Good vascular (blood) supply • maintains concentration gradients

  8. Each filament is made of thin delicate plates (lamellae) containing many capillaries, so they look dark red.

  9. Ventilation • The fish opens its mouth and lowers its buccal floor, increasing the volume in the mouth and so decreasing the pressure • Water rushes in • The fish closes its mouth and raises its buccal floor • This decreases the volume, and so increases the pressure in the mouth • Water is forced over the gills and out of the operculum • Gas exchange happens in the gills

  10. Gas Exchange • Capillaries and lamellae have thin walls. O2 and CO2 diffuse through easily. • Gases move by diffusion. • O2 into capillaries • CO2 into water

  11. How does it work? In a concurrent (parallel) flow system, blood and water flow in the same direction. O2 concentration will reach an equilibrium.

  12. CONCURRENT FLOW

  13. Counter-Current Exchange • The blood flow in the capillaries is opposite to the flow of water over the gills. • This means that the blood in the capillary is always meeting new water with a full load of oxygen. • Counter current exchange of water flow and bloodstream maintains concentration gradients for diffusion.

  14. COUNTER-CURRENT FLOW

  15. Why don’t fish drown? • Oxygen is 21% of air; < 1% of water • More water can flow over (external) gills than in and out of (internal) lungs. • Countercurrent flow in gills extracts more of the oxygen from the water in a low O2 environment. • Fish demand for O2 supply and removal of CO2 is lower than larger animals

  16. The gill gas exchange system limits fish to a watery environment. • The watery environment does not require the gas exchange surface to be internal.

  17. How is the structure of the gills related to its function? Think: Specialised exchange surface SA/V ratio Gas Exchange Blood flow

  18. Homework Bring a fish head to the lesson on Wednesday.

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