Download Gas Exchange in Animals

Gas Exchange in Animals
Weta
 Gas exchange occurs in the twigs of air-filled branching tubes called tracheae,
which extend through the entire body.
 Blood plays no part in oxygen transport, which is carried out by the tracheal
system itself.
 Diffusion is fast enough when the insect is resting, but when it is active, air is
pumped in and out of the tracheal system by muscular action.
 Though weta live in dry environments, the air in contact with the gas exchange
surface is humid since the tracheae are deep intuckings into the body.
 Water loss by evaporation is regulated by partial closure of the spiracles except
when the insect is active.
Trout
 Fish breathe by gills which unlike lungs, are outpushings of body into the
environment.
 As in mammals, gases are transported to and from the gas exchange surface by
blood.
 Though the amount of oxygen that can be dissolved in water is much less than
that in air, gills can be ventilated unidirectionally.
 Unidirectional ventilation makes it possible for blood and water to flow in
opposite directions, enabling a high proportion (80%) of the oxygen to be
extracted (in a mammal, less than 25% of the inhaled oxygen is extracted)
 In a well oxygenated stream, the concentration of dissolved oxygen may be higher
than the concentration of dissolved oxygen in the fluid lining the alveoli of a
mammal.
 Nevertheless, the oxygen dissolved in the alveolar walls and plasma is in
equilibrium with a far greater amount of oxygen in the air in the lungs. Hence
when a fish stops breathing there is a rapid fall in the oxygen content of the
blood leaving the gills; in a mammal there is a considerable quantity of oxygen
stored in the lungs.
Mammals
 As in insects, the gas exchange surface is a deep, richly branched air-filled
intucking into the body.
 Unlike insects, the gas exchange surface is distant from most of the cells of the
body. The blood being responsible for the transport of gases.
 Since ventilation is tidal and only a small proportion of the air is renewed each
breath, the air at the gas exchange surface has a significantly lower oxygen
concentration and higher CO2 concentration than that of the atmosphere.
 This partial renewal of air enables the gas exchange surface to be saturated with
water vapour, thus greatly reducing water loss.