1. Gas Exchange in Animals
O2 diffuses in, CO2 diffuses out
Exchange surface must be moist
All living cells bathed in water to maintain plasma membranes
Rate of diffusion is proportional to surface area
Rate of diffusion is inversely proportional to distance2

2. Mechanisms of Gas Exchange
Over entire body surface
protists, unicellular organisms, some simple animals (sponges, flatworms)
Outer skin as respiratory organ
Typically long, thin flat organisms with large SA/volume ratio
Ex: earthworm, some amphibians/ moist skin, dense net of capillaries just below skin
Respiratory organs
Designed to increases surface area
Gills, trachae, and lungs

3. Gills Respiratory adaptation for most aquatic animals
Outfoldings of body surface
SA of gills is normally > SA of rest of body
Note [O2] in water is fairly low as compared to [ ] in air.
Ventilate gills – constantly move water over gills/requires considerable energy
Counter current exchange
Water moves over gills in one direction, blood flows in opposite direction
Favors transfer of oxygen from water to blood

4. Figure 42.0 External gills of a salmon

5. Figure 42.21 Countercurrent exchange

6. Advantages/Disadvantages of Air as a Respiratory Medium
Large surface area leads to increased evaporation of water
Advantages
210 mL O2 per L in air vs 8 mL per L in water
Diffusion is faster in air than in water
Easier to move air than water when respiratory surface needs to be ventilated
Ventilation does not have to be as extensive

7. Trachael System Typically found in insects
Air tubes that branch throughout the body
Deliver air directly to all body cells
Open circulatory system is not involved in transporting O2 and CO2
Trachae are large tubes that open to outside, branch extensively inside insect’s body
Spiracles = openings on insects body surface
Ventilate with rhythmic body movements

8. Lungs Restricted in location
Not in direct contact with all other parts of the body
Need closed circulatory system to transport gases between lungs and the rest of the body
Used by spiders, terrestrial snails, amphibians (also body breathe), most reptiles, lungfish, birds, mammals

9. Air Flow Nasal Cavity (warm and filter air) Pharynx Larynx Trachea
Bronchus (2 bronchi/ one right / one left)
Bronchioles
Alveoli
huge SA
moist film covers surface
sites of gas exchange

10. Figure 42.23ab The mammalian respiratory system

11. Structure of Alveoli

12. (+) vs (–) Pressure Breathing
(+) = frog
(-) = us

13. Figure 42.24 Negative pressure breathing

14. Lung Volumes Tidal Volume Vital Capacity Residual Volume
Volume of air inhaled or exhaled in a normal breath
Typically 500 mL in resting humans
Vital Capacity
The maximum tidal volume
Typically 3.4 to 4.8 L
Residual Volume
Volume of air remaining in lungs after we forcefully exhale as much air as we can

15. Control of Breathing
CO2 levels rather than O2 levels are most important indicator
Control is automatic
Control centers in medulla oblongata and pons
Medulla oblongata sets breathing rhythm
Use (-) feedback mechanisms
Decrease in pH means increase in CO2
Stimulate respiration
Increase depth and rate of breathing
O2 used as signal at high altitudes/O2 sensors in carotids and aorta

16. Figure 42.26 Automatic control of breathing

17. Partial Pressure of Gases
P1 + P2 + P3 + … → PTotal
Diffuse from area of high partial pressure to an area of low partial pressure
Blood arrives at lungs with low PO2 and high PCO2 relative to atmosphere

18. O2 transport
Transport proteins used to increase the efficiency of oxygen transport
Only 4.5 mL dissolved O2/L of blood
Hemocyanin
Found in hemolymph of arthropods and mollusks
Copper containing cofactor
Hemoglobin
Found in blood
4 subunits
Iron containing heme cofactor
Carries 4 molecules of oxygen

19. CO2 transport 7% dissolved in solution 23% bound to hemoglobin
70% in the form of bicarbonate ion

20. Figure 42.29 Carbon dioxide transport in the blood

21. Hemoglobin Dissociation Curves
Bohr effect at lower pH
Additional oxygen is released at lower pH

22. Figure 42.28 Oxygen dissociation curves for hemoglobin

23. Unnumbered Figure (page 899) Dissociation curves for two hemoglobins