Gas Exchange Fish Flashcards
What is the surface area to volume ratio of fish?
Small surface area to volume ratio
What special exchange surface have fish evolved?
Gills
Why have fish evolved gills?
- Body surface is not adequate to supply and remove respiratory gasses
- They have therefore evolved a specialised internal gas exchange surface called gills
Where are the gills located?
Within the body of the fish, behind the head.
What are gills made up of?
- Gill filaments
* At right angles to gill filaments are gill lamellae
What is the structure of gill filaments?
• Stacked up
What is the purpose of gill filaments?
• Increase the surface area of the gills
How is water taken in the fish?
• Taken in through the mouth, forced over the gills and out through the opening on each side of the body
What is the counter current flow in fish?
• Flow of water over the gill lamellae and the flow of blood within them are in opposite directions
Why is counter-current exchange needed?
- Ensures that the maximum possible gas exchange is taking place.
- If blood & water flowed in the same direction, far less gas exchange would be taking place
- Maintains the concentration gradient between water and blood
- Concentration of oxygen is always higher than the concentration of the blood, so a high amount of oxygen diffuses
What direction does blood & water flow in counter current exchange?
Opposite directions
How does counter current exchange work?
• Blood that is loaded with oxygen meets water that has a maximum concentration of oxygen
• This results in diffusion of oxygen from water to the blood
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• Blood with little oxygen in it meets water which has had most of its oxygen removed
• Diffusion of oxygen from water to the blood will occur
What do the lamellae have to speed up diffusion?
• Thin surface layer of cells and many blood capillaries
