Lecture 5. Gas Exchange

• cellular respiration, oxidative processes within cells

• external respiration, exchange of O2 and CO2 between the organism and its environment

Gas Exchange Surfaces

• for diffusion to be effective, gas-exchange regions must be:– moist– thin– relatively large

• effectiveness of diffusion is enhanced by vascularization

• cutaneous respiration (direct diffusion)

Respiratory Organs

Respiratory Organs

• Tracheal systems (branching system of tubes)

Respiratory Organs

• Gills or branchia (external or internal)

papulae (dermal branchiae or skin gills)

Respiratory Organs

• Gills or branchia (external or internal)

branchial tufts (gills) in marine worm

gills in axolotl (Ambystoma mexicanum)

Respiratory Organs

• Gills or branchia (external or internal)

parapodia in ragworm (Nereis spp.)

Respiratory Organs

• Gills or branchia (external or internal)

How a fish ventilates its gills

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countercurrent flow/exchange

Respiratory Organs

• Lungs (invaginations)

A frog ventilates its lungs by positive pressure breathing.

• Lungs of frogs

• Lungs of mammals

Mammals ventilate their lungs by negative pressure breathing.

• Lungs of mammals

• Lungs of birds

http://www.peteducation.com/article.cfm?c=15+1829&aid=2721

• Lungs of birds

http://www.peteducation.com/article.cfm?c=15+1829&aid=2721

• the volume of air an animal inhales and exhales with each breath is called tidal volume– it averages about 500 mL in resting humans

• the maximum tidal volume during forced breathing is the vital capacity– about 3.4 L and 4.8 L for college-age females and

males, respectively

• most animals transport most of the O2 bound to special proteins called respiratory pigments– hemocyanin– hemoglobin

• when the control center registers a slight drop in pH, it increases the depth and rate of breathing, and the excess CO2 is eliminated in exhaled air

• O2 diffuses into pulmonary capillaries

• most O2 combines with hemoglobin in red blood cells to form oxyhemoglobin

• CO2 diffuses out of pulmonary capillaries

• most CO2 is transported in the form of bicarbonate ion

• some CO2 combines with hemoglobin to form carbaminohemoglobin

Fig. 31.27

• cooperative oxygen binding and release is evident in the dissociation curve for hemoglobin

• a drop in pH lowers the affinity of hemoglobin for O2, an effect called the Bohr shift