Counter current flow
The counter current system maintains a diffusion gradient along the whole length of the gill plate.
There is only a counter current flow in bony fish.
- Specialised mechanism for ventilation ensures blood and water flow in opposite directions.
- Water always has a higher oxygen concentration than blood in capillaries.
- Oxygen diffuses into gill capillaries across entire length of lamellae.
- Gill absorbs about 80% of oxygen from water across gills.
As distance across lamellae increases:
- % oxygen in blood increases
- % oxygen in water decreases
- Maintain concentration gradient across whole gill lamellae
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