Requirements for Gas Exchange

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Requirements for Gas Exchange moist
membrane surface area respiratory medium Air
Water
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Gills
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Ventilation, which increases the flow of the
respiratory medium over the respiratory surface,
ensures that there is a strong diffusion gradient
between the gill surface and the
environment. Crayfish and lobsters have
paddlelike appendages that drive a current of
water over their gills. Fish gills are
ventilated by a current of water that enters the
mouth, passes through slits in the pharynx, flows
over the gills, and exits the body.
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Ventilation - gill cover
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Terrestrial organisms Gills unsuited for an
animal living on land.
Air- respiratory medium Advantages of air over
water higher concentration of oxygen. O2 and CO2
diffuse much faster in air less energy is needed
to ventilate
Disadvantages of air as a respiratory
medium loss of water Terrestrial respiratory
surfaces within the body opening to the
atmosphere through narrow tubes.
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Insects - tracheal system Trachea Gas exchange
at cell by diffusion across the moist epithelium
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Lungs Amphibians lungs skin Reptiles, Birds
Mammals - only lungs
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Ventilation - (breathing) Inhalation
Exhalation Amphibians - Positive pressure
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Lung Volumes - Residual Volume differences