- Fish have a small surface area to volume ratio
- This means the surface can't supply enough respiratory gases - so fish developed gills
Fish Gills
- Fish gills are behind their head
- Made up of many gill filaments stacked in a pile
- Gill lamellae at right angles to the filaments to increase surface area
- Water taken in through their mouth
- Water then forced over the gills and out through the opening on each side of their body
Countercurrent Flow (parallel flow wouldn't work!)
- Flow of water over the lamellae is in the opposite direction o the flow of blood within the lamellae
- Ensures the largest diffusion gradient between the water and blood at all times
- Blood loaded with oxygen meets water high in oxygen- diffusion oxygen from water to the blood
CONCENTRATION GRADIENT IS MAINTAINED ALONG THE LENGTH OF THE GILLS WITH THE COUNTERCURRENT PRINCIPLE
Gill adaptions
- Large surface area (from the lamellae and filaments) - increases diffusion
- Short distance between the water and the blood
- Countercurrent Flow
- Circulation (replaces blood saturated with oxygen)
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