gas exchange in fish

features of fish

waterproof and therefore gas-tight outer covering

relatively large so small SA:V ratio

structure of the gills

- behind the head

- made up of gill filaments stacked in a pile

- at right angles to gill filaments are gill lamellae

function of gill lamellae

increase surface area of gills

water taken in through the mouth...

forced over the gills and out through an opening on each side of the body

What is countercurrent flow?

flow of water over gill lamellae and the flow of blood within them are in opposite directions

The tips of filament overlap. How does this affect water flow?

slows water flow so more time for diffusion to take place

How does the counter current exchange system work?

- blood and water flow over gill lamellae in opposite directions

- so blood well loaded with oxygenmeets water (maximum conc. of oxygen)

- therefore diffusion of oxygen from the water to the blood takes place

- water that exits the capillary has the lowest oxygen concentration, and is adjacent to the most deoxygenated blood

- diffusion gradient for oxygen uptake maintained

Why would parallel/councurrent flow be bad?

the concentration of oxygen in the water and in the blood will equalise so no more oxygen exchange would take place