Gas exchange in fish Flashcards
Where are the gills located?
Within the body, behind the head.
What are gills made up of?
1) Gill filaments - They are stacked up in piles, like pages in a book.
2) At right angle to the filaments are gill lamellae, this increases the SA of the gills.
How is water taken in by the fish?
Fish opens its mouth and fills with oxygenated water while the operculum is closed and as the fish closes its mouth, the operculum opens and the oxygenated water is pumped across the gills.
How does the water and blood flow within a fish?
The flow of water goes over the lamellae and the flow of blood within them are in opposite directions - countercurrent flow.
Why do water and blood do not flow in the same direction?
Because less gas exchange would take place and fishes have a small SA:V so they need the maximum possible gas exchange to be achieved.
How are gills adapted for the maximum efficiency of gas exchange in fish?
Blood flows through the capillaries within the lamellae, O2 diffuses from the water to the blood. It also provides a very large respiratory SA and has a counter-current exchange system.
How does the counter current exchange system work?
As blood flows in one direction, water flows in the opposite direction.
- When water just been taken in by the fish, it is fully oxygenated - 100% and it gradually gets lower, 100-70-40-15…
- However as the blood meets with the water, the blood at the start is very deoxygenated because it has just been used up by the body. So it might start as 5% and gradually getting higher because oxygen from the water is diffused into the blood down the concentration gradient. 5-30-60-80…
- Even till the very end of the lamellae, oxygen still diffuse across from the water into the blood because there is still a difference in the concentration gradient.
- So blood is loaded with more O2 as it flows through the lamellae and it always passed through water which is more and more oxygenated therefore allowing for maximum oxygen diffusion down its concentration gradient from water into the blood.
Why is counter current exchange system efficient for gas exchange?
Because it maintains a high concentration gradient down which O2 diffuses over the whole length of the gill.
