Transcript Fish Gas Exchange - Learning on the Loop

Review – factors needed for
efficient gas exchange
• Large surface area
• Moist surface to dissolve gases
• Concentration Gradient
The Gill Gas Exchange
• Fish have gills over
which water
continually flows.
• Gills are supported by
water flowing over
them, so are
unsuitable for life on
dry land.
• The water has oxygen
dissolved in it.
Fish Anatomy
Mouth (Buccal
Cavity)
Operculum
Buccal Floor
Behind the Operculum…
…lie the gills – the fish’s
equivalent of our lungs
Gill Structure
• Gill arches
• Gill filaments
• Lamellae
Adaptations of the gills for efficient
gas exchange
• Large surface area : volume
– allows more diffusion of gases
• Permeable membranes
– allows gases to diffuse through tissues
• Thin (flattened cells)
– short diffusion distance
• Good vascular (blood) supply –
– maintains concentration gradients
Structure of Gills
• The gills are made of numerous thin filaments
supported by a bony arch.
• Each filament is made
of thin delicate plates
(lamellae) containing
many capillaries, so
they look dark red.
• gills are protected by an
operculum.
Ventilation
• The fish opens its mouth and lowers its buccal floor,
increasing the volume in the mouth and so decreasing
the pressure
• Water rushes in
• The fish closes its mouth and raises its buccal floor
• This decreases the volume, and so increases the
pressure in the mouth
• Water is forced over the gills and out of the operculum
• Gas exchange happens in the gills
Exchange and Diffusion of Gases.
• The capillaries have very thin
walls that allow the O2 to
move from the water into the
blood and CO2 from the blood
into the water by diffusion.
• O2 moves from where there is
a high concentration in the
water to where there is a
lower concentration in the
blood of the capillaries.
• CO2 moves from where there
is a high concentration in the
capillary blood to where there
is a low concentration in the
water.
Counter-Current Exchange
• The blood flow in the capillaries is opposite to the flow of
water over the gills.
• This means that the blood in the capillary is meeting new
water with a full load of oxygen.
• Counter current exchange of water flow and blood stream
maintains concentration gradients for diffusion.
Counter Current Principle
Animation of counter-current
Efficiency of Counter-current
Exchange
• Counter-current exchange removes up to 80% of
the oxygen in the water.
Gills greatly increase the surface
area for gas exchange.
Thin Exchange Surface
• Thin walls of
lamellae and
capillaries to
↓ barrier for
diffusion of
O2 into
capillaries
and CO2 out
Moist Gas Exchange Surface
• Moist surface
maintained by
watery
environment.
• O2 already
dissolved into
watery
substance for
diffusion into
capillaries.
Why don’t fish drown?
• Oxygen is 21% of air, <
1% in water
• More water can flow over
(external) gills than in and
out of (internal) lungs.
• Countercurrent flow in
gills extracts more of the
oxygen from the water in
a low O2 environment.
• Fish demand for O2
supply and removal of
CO2 is lower than larger
animals
• The gill gas exchange
system limits fish to a
watery environment.
• The watery
environment does not
require the gas
exchange surface to
be internal.