classnotes4 - Gas exchange: Respiratory organs: -...

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Gas exchange: Respiratory organs: - essentially a system that provides oxygen to the organism. Usually, the circulatory system (if present) then delivers this to the cells, but oxygen needs to be put into the circulatory system to begin with. Thus, respiratory organs have developed. - Many different kinds: - skin - gills - trachea - lungs - others (e.g. book lungs) - All share the characteristic that the surface where gas exchange takes place is moist. Diffusion must take place across a moist surface. 1) skin [Fig. 22.2A, p. 455] : - if this is used exclusively, then it only works for smaller organisms, since the surface area provided by skin is not very large. Earthworms, and some amphibians (some amphibians do not have lungs) are a good example (note that their skin is always moist). [Reptiles are not “slimy”, but many amphibians are.] 2) gills [FIG. 22.2B, p. 455] : - used by many aquatic organisms, and just a few terrestrial ones. Idea is to produce a structure with a very folded outer surface. This increases surface area dramatically. Blood is then pumped through the gills, and picks up oxygen/gives up carbon dioxide. This is made more efficient with a counter current system [Fig. 22.3, and not in book] . - counter current - in a nutshell, things never reach equilibrium, as they would in “same”, or “con” current flow. See overhead. Gases (or heat) can be exchanged along the entire length of the exchange. - counter current ideas also help preserve heat (illustrate)
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classnotes4 - Gas exchange: Respiratory organs: -...

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