Requirements for Gas Exchange moist membrane surface area respiratory medium Air Water.

• Gas exchange, in concert with the circulatory system,provide the oxygen necessary for aerobic cellular respirationand removes the waste product, carbon dioxide.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 42.18

Requirements for Gas Exchangemoist membranesurface arearespiratory medium

Air Water

• In some invertebrates, such as sea stars, the gills have asimple shape and are distributed over much of the body.

• Many segmented wormshave flaplike gills thatextend from eachbody segment, or longfeathery gills clusteredat the head or tail.

• The gills of clams,crayfish, and manyother animals arerestricted to a localbody region.


Fig. 42.19

Gills

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.


Fig. 42.20

Ventilation - gill cover

• This flow pattern is countercurrent exchange.

• As blood moves anteriorly in a gill capillary, it becomesmore and more loaded with oxygen, but itsimultaneously encounters water with even higheroxygen concentrations because it is just beginning itspassage over the gills.

• All along the gillcapillary, there is adiffusion gradientfavoring the transferof oxygen fromwater to blood.


Fig. 42.20

Terrestrial organismsGills unsuited for an animal living on land.

Air- respiratory medium

Advantages of air over waterhigher concentration of oxygen.O2 and CO2 diffuse much faster in air less energy is needed to ventilate

Disadvantages of air as a respiratory mediumloss of water

Terrestrialrespiratory surfaces within the bodyopening to the atmosphere through narrow tubes.


Fig. 42.22

Insects - tracheal system TracheaGas exchange at cell by diffusion across the moist epithelium


Fig. 42.23

LungsAmphibians lungs & skinReptiles, Birds & Mammals - only lungs

• In contrast, mammals ventilate their lungs bynegative pressure breathing.

• This works like a suction pump, pulling air instead ofpushing it into the lungs.

• Muscle action changes the volume of the rib cage and thechest cavity,and the lungsfollow suit.


Fig. 42.24

Ventilation - (breathing) Inhalation Exhalation

Amphibians - Positive pressure

• Ventilation is much more complex in birds than inmammals.

• Besides lungs, birds have eight or nine air sacs that donot function directly in gas exchange, but act as bellowsthat keep air flowing through the lungs.


Fig. 42.25

Lung Volumes - Residual Volume differences

Requirements for Gas Exchange moist membrane surface area respiratory medium Air Water.

Documents

moist epithelium slide

ventilation gill cover

current of water

disadvantages of air

fish gills

terrestrial organisms

gill surface

strong diffusion gradient