1. Chapter 44
Gas Exchange

2. Respiration
The exchange of gases between an organism and its environment
Organismic respiration
Takes place in animals
O2 taken up and CO2 excreted
Aerobic cellular respiration
Takes place in mitochondria
O2 is necessary for citric acid cycle

3. Simple diffusion
Passive movement of particles from a region of higher concentration to a region of lower
Provides gas exchange for small, aquatic organisms such as sponges, hydras, and flatworms

4. Comparison of gas exchange in air and water
Contains a higher concentration of molecular oxygen than water
Oxygen diffuses more rapidly through air than water
Less energy needed to move air over gas exchange surface

5. Adaptations for gas exchange
Body surface
Small aquatic animals exchange gases by diffusion, requiring no specialized respiratory structures
Some invertebrates, including most annelids, and many amphibians exchanges gases across the body surface

6. Gas exchange across body surface

7. Adaptations for gas exchange, cont’d
Trachae
In insects and some other anthropods, air enters trachae through openings called spiracles
Trachae branch and extend to all regions of the body

8. Gas exchange across tracheal tubes

9. Adaptations for gas exchange, cont.
Gills
Moist, thin projections of the body surface found mainly in aquatic animals
Countercurrent exchange system maximizes O2 into the blood and CO2 out of the blood

10. Gas exchange across gills

11. Adaptations for gas exchange, cont.
Lungs
Terrestrial vertebrates have lungs and some means of ventilating them
Lungs are respiratory structures that develop as ingrowths of body surface or from wall of a body cavity

12. Gas exchange across lungs

13. Comparison of vertebrate lungs

14. How bird lungs function

15. Mammalian respiratory system
Includes the lungs and airways
Lung occupies pleural cavity and is covered with a pleural membrane
Breath of air passes in sequence
Nostrils, nasal cavities, pharynx, larynx, trachea, bronchi, bronchioles, and alveoli

16. The human respiratory system

17. Structure of alveoli

18. Mechanics of breathing
Diaphragm contracts and chest cavity expands
Respiratory centers in the medulla and pons regulate respiration
Stimulated by chemoreceptors
An increase in hydrogen ions and low oxygen concentration

19. Mechanics of breathing

20. Role of hemoglobin in oxygen transport
Respiratory pigment in vertebrate blood
Almost 99% of the O2 in human blood is transported as oxyhemoglobin (HbO2 )

21. Gas exchange in the lungs and tissues

22. Oxygen-carrying capacity
Maximum amount of O2 that can be transported by hemoglobin
Oxygen content
Actual amount of O2 bound to hemoglobin
Percent oxygen saturation
Ratio of O2 content to O2 carrying capacity

23. Oxygen-hemoglobin dissociation curve
Shows that as O2 concentration increases, there is progressive increase in hemoglobin that combines with O2
Bohr effect
Oxyhemoglobin dissociates more readily as CO2 increases

24. Oxygen-hemoglobin dissociation curves

25. Carbon dioxide transport

26. Decompression in divers
Hyperventilation
Reduces the concentration of CO2 in the alveolar air and the blood
Decompression in divers
Rapid decrease in barometric pressure can cause decompression sickness
Diving mammals have high concentrations of myoglobin

27. Deep diver

28. Affects of pollution on the respiratory system
Ciliated mucous lining traps inhaled particles
Inhaling polluted air results in bronchial constriction
Increased mucous secretion
Damage to ciliated cells
Coughing