gas exchange in fish

structure of exchange system?

• gills made up of gill filaments → large SA

• each filament covered in lamellae increasing SA

• lamellae have thin epithelium walls → short diffusion distance

• each lamellae contain network of capillaries to maintain concentration gradient

process of gas exchange?

• water enters mouth, flows over gill filaments and lamellae

• O2 diffuses from water into blood across the thin lamellae epithelium

• CO2 diffuses from blood into water

• blood in lamellae flows in opp direction to water

• counter-current flow maintains steep conc. gradient

• allowing for max O2 diffusion into blood

how does the counter current flow maintain a concentration gradient?

water + blood flow in opposite directions across lamellae
blood w lower oxygen conc. always passes by water with higher oxygen conc.
creating a steep conc. gradient so that diffusion occurs along whole gill
ensuring maximum O2 uptake

what is the countercurrent flow?

• blood and water flow in opp. directions across lamellae

• blood w lower oxygen conc. always passes water higher oxygen conc.

• maintains a conc. gradient along whole length of gill allowing for max. diffusion

why is countercurrent flow necessary?

if flow was parallel, equilibrium would be reached, so O2 wouldn’t diffuse into blood across whole gill