Fish - Gas exchange system Flashcards
Why do fish require a specialised exchange surface?
Fish have a water proof (therefore gas tight) outer covering
Their SA:V ratio is too small to exchange across their surface alone anyway
What are fish gills ?
They are the fishs equivalent of our lungs
They are behind the operculum
Water continually flows over the gills
The water has oxygen dissolved in it
Why do gills have to be very efficient at extracting oxygen from water
Because water contains ≈1% oxygen
How are gills adapted for gas exchange (large SA)
•Many filaments & lamella -> large SA
How are gills adapted for gas exchange? (short diffusion pathway)
Only 2 flattened cells separate water and blood :
- Epithelial layer of lamella
- Endothelial layer of blood capillaries
How are gills adapted for gas exchange?
(diffusion al gradient)
Each lamellae has its own capillary network
—> movement of blood and water maintain diffusion gradient
What type of ventilation do fish have?
Unidirectional ventilation
IN ————-> OUT
What is counter current flow?
•Blood and water flow in opposite directions
•Maintains concentration gradient
•Circulatory system = removes oxygenated blood and replaces it with deoxygenated = low oxygen concentration in blood
•Ventilation of water through the gills = oxygen concentration as high as possible in the water
Why doesn’t a parallel flow
of blood and water work in fish gills?
Diffusion gradient favours the diffusion of oxygen from water to blood for only part of the way across the gill lamella
- Only 50% of the oxygen from the water diffuses into the blood
-Equilibrium is reached and so diffusion stops
Why does the counter current flow work in fish
Diffusion gradient favouring the diffusion of oxygen from water into the blood all the way across the gill lamellae
Almost all the oxygen from the water diffuses into the blood
Equilibrium is never reached and a diffusion gradient is maintained across the entire lamellae
What are the advantages of the counter current system
An oxygen conc gradient is always maintained so oxygen can constantly move into the blood
2) The whole length of the lamellae can be used for exchange
3) An equilibrium is never reached
How does the counter current flow maintain a concentration gradient
water always meets blood with a lower conc of oxygen
Blood flow takes away blood with a high conc of oxygen & brings in blood with low conc of oxygen
Ventilation brings in water with high conc of oxygen a low conc of carbon dioxide
