2/6/2012
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Circulatory Systems
Exchange with the environment
•All animal cells must have enough surface area
to allow sufficient environmental exchange of
O2, nutrients & wastes
•Environmental exchange requires a
fluid/aqueous environment for the cells
•For most cells making up multicellular organisms,
direct exchange with the environment is not possible
•Gills are an example of a specialized exchange system
in animals
–O2 diffuses from the water into blood vessels
–CO2 diffuses from blood into the water
•Internal transport and gas exchange are functionally
related in most animals
© 2011 Pearson Education, Inc.
Circulatory Systems
•Move E, nutrients, wastes, O2 from one part of the
body to another
•In small and/or thin animals, cells can exchange
materials directly with the surrounding medium
•In most animals, transport systems connect the
organs of exchange with the body cells
•Most complex animals have internal transport
systems that circulate fluid
Animals w/ No Circulatory System
•Gastrovascular Cavity
•May be highly branched
•No additional internal
transport system needed
•Nutrients, gases, wastes
diffuse short distances
Gastrovascular
cavity
Mouth
Pharynx
2 mm
Evolutionary Variation in Circulatory
Systems
•A circulatory system minimizes the diffusion distance in
animals with many cell layers
•The circulatory system connects the fluid that
surrounds cells with the organs that exchange gases,
absorb nutrients, and dispose of wastes
•Circulatory systems can be open or closed and vary in
the number of circuits in the body
© 2011 Pearson Education, Inc.
