1. Gas Exchange
Chapter 45

2. Learning Objective 1
Compare the advantages and disadvantages of air and water as mediums for gas exchange
Describe adaptations for gas exchange in air

3. Gas Exchange in Air and Water
Air has a higher concentration of molecular oxygen than does water
Oxygen diffuses faster through air than through water
Air is less dense and less viscous than water (less energy needed to move air over gas exchange surface)

4. Terrestrial Animals
Have adaptations that protect their respiratory surfaces from drying

5. KEY CONCEPTS
Air has a higher concentration of molecular oxygen than water does, and animals require less energy to move air than to move water over a gas exchange surface
Adaptations in terrestrial animals protect their respiratory surfaces from drying

6. Learning Objective 2
Describe the following adaptations for gas exchange: body surface, tracheal tubes, gills, and lungs

7. Adaptations for Gas Exchange 1
Small aquatic animals
exchange gases by diffusion
no specialized respiratory structures
Some invertebrates (most annelids) and some vertebrates (many amphibians)
exchange gases across body surface

8. Adaptations for Gas Exchange 2
Insects and some other arthropods
air enters network of tracheal tubes (tracheae) through spiracles along body surface
tracheal tubes branch, extend to all body regions

9. Tracheal Tubes

10. (a) Location of spiral and tracheal tubes.
Spiracle
Figure 45.2: Tracheal tubes.
Tracheal tube
(a) Location of spiral and tracheal tubes.
Fig. 45-2a, p. 973

11. (b) Structure and function of a tracheal tube.
Epithelial cell O2
Tracheal tube
Tracheole
Spiracle
CO2
Figure 45.2: Tracheal tubes.
Muscle
(b) Structure and function of a tracheal tube.
Fig. 45-2b, p. 973

12. Figure 45.2: Tracheal tubes.
Fig. 45-2c, p. 973

13. Adaptations for Gas Exchange 3
Aquatic animals have gills
thin projections of body surface
Chordates
gills usually internal, along edges of gill slits

14. Adaptations for Gas Exchange 4
Bony fishes
operculum protects gills
countercurrent exchange system maximizes diffusion of O2 into blood, CO2 out of blood
Animals carry on ventilation
actively move air or water over respiratory surfaces

15. Gills in Bony Fishes

16. Gill arch CO2 O2 Opercular chamber (a) Location of gills.
Figure 45.3: Gills in bony fishes.
Opercular chamber
(a) Location of gills.
Fig. 45-3a, p. 974

17. Gill arch Blood vessels Gill filaments (b) Structure of a gill.
Figure 45.3: Gills in bony fishes.
(b) Structure of a gill.
Fig. 45-3b, p. 974

18. Efferent blood vessel (rich in O2)
Afferent blood vessel
(low O2 concentration)
Figure 45.3: Gills in bony fishes.
Efferent blood vessel (rich in O2)
(c) Countercurrent flow.
Fig. 45-3c, p. 974

19. Figure 45.3: Gills in bony fishes.
Fig. 45-3d, p. 974

20. Figure 45.3: Gills in bony fishes.
Fig. 45-3e, p. 974

21. Adaptations for Gas Exchange 5
Terrestrial vertebrates have lungs
and some means of ventilating them
Amphibians and reptiles have lungs
with some ridges or folds that increase surface area

22. Adaptations for Gas Exchange 6
In birds
lungs have extensions (air sacs) that draw air into system
2 cycles of inhalation and exhalation

23. Gas Exchange in Birds One-way flow of air through lungs
from outside into posterior air sacs, to lung, through anterior air sacs, out of body
Gas exchanged through walls of parabronchi
crosscurrent arrangement (blood flow at right angles to parabronchi) increases amount of O2 entering blood

24. Gas Exchange in Birds

25. Anterior air sacs Posterior air sacs
Trachea
Airsacs
Air
Lung
Anterior
air sacs
Posterior
air sacs
(a) Structure of the
bird respiratory
system.
(b) First inhalation. As the bird inhales, fresh air flows into the posterior air sacs (blue) and partly into the lungs (not shown).
(c) First exhalation. As the bird exhales, air from the posterior air sacs is forced into the lungs.
(d) Second inhalation. Air from the first breath moves into the anterior air sacs and partly into the lungs (not shown). Air from the second inhalation flows into the posterior air sacs (pink).
(e) Second exhalation. Most of the air from the first inhalation leaves the body, and air from the second inhalation flows into the lungs.
Figure 45.5: Gas exchange in birds.
The bird respiratory system includes lungs and air sacs. The bird’s breathing process requires two cycles of inhalation and exhalation to support a one-way flow of air through the lungs.
Fig. 45-5, p. 975

26. Evolution of Vertebrate Lungs

27. Trachea To other lung Salamander's lungs Frog's lungs Toad's lung
Figure 45.4: Evolution of vertebrate lungs.
The surface area of the lung has increased during vertebrate evolution. Salamander lungs are simple sacs. Other amphibians and reptiles have lungs with small ridges or folds that help increase surface area. Birds have an elaborate system of lungs and air sacs. Mammalian lungs have millions of alveoli that increase the surface available for gas exchange (see Fig. 45-7).
Air sac
Air sac
Bird's lungs
Reptile's lung
Fig. 45-4, p. 975

28. Adaptations for Gas Exchange

29. Earthworm (a) Body surface. Fig. 45-1a, p. 972
Figure 45.1: Adaptations for gas exchange.
Earthworm
(a) Body surface.
Fig. 45-1a, p. 972

30. Grasshopper (b) Tracheal tubes. Fig. 45-1b, p. 972
Figure 45.1: Adaptations for gas exchange.
(b) Tracheal tubes.
Fig. 45-1b, p. 972

31. External gills Internal gills Gills Fish Mud puppy (c) Gills.
Figure 45.1: Adaptations for gas exchange.
Fish
Mud puppy
(c) Gills.
Fig. 45-1c, p. 972

32. Book lung Lungfish Spider Mammal (d) Lungs. Fig. 45-1d, p. 972
Figure 45.1: Adaptations for gas exchange.
(d) Lungs.
Fig. 45-1d, p. 972

33. Learn more about adaptations for gas exchange, including gills in bony fishes, vertebrate lungs, and the bird respiratory system, by clicking on the figures in ThomsonNOW.

34. KEY CONCEPTS
Adaptations for gas exchange include a thin, moist body surface; gills in aquatic animals; and tracheal tubes and lungs in terrestrial animals

35. Learning Objective 3
Trace the passage of oxygen through the human respiratory system from nostrils to alveoli

36. The Human Respiratory System
Includes lungs and system of airways
Each lung occupies a pleural cavity and is covered with a pleural membrane
Air passes through nostrils, nasal cavities, pharynx, larynx, trachea, bronchi, bronchioles, alveoli

37. The Human Respiratory System

38. Sinuses Respiratory centers Nasal cavity Tongue Epiglottis Pharynx
Larynx
Esophagus
Trachea
Bronchioles
Space
occupied
by heart
Figure 45.6: The human respiratory system.
The internal view of one lung illustrates a portion of its extensive system of air passageways. The muscular diaphragm forms the floor of the thoracic cavity. The respiratory centers in the brain regulate the rate of respiration.
Bronchus
Right lung
Left lung
Diaphragm
Fig. 45-6, p. 976

39. Structure of Alveoli

40. Epithelial cell of the wall of the alveolus
Capillary
Red
blood
cells
Bronchiole
Alveolus
Macrophage
Capillaries
Alveolus
Alveolus
Figure 45.7: Structure of alveoli.
Epithelial cell of the wall of the alveolus
Epithelial cell of the adjacent alveolus
(a)
Fig. 45-7a, p. 977

41. Figure 45.7: Structure of alveoli.
Fig. 45-7b, p. 977

42. Wall of alveolus Red blood cell Wall of capillary 1 µm (c)
Figure 45.7: Structure of alveoli.
1 µm
(c)
Fig. 45-7c, p. 977

43. Insert “Human respiratory system”
human_respiratory_v2.swf

44. Learn more about the human respiratory system by clicking on the figures in ThomsonNOW.

45. Learning Objective 4
Summarize the mechanics and the regulation of breathing in humans
Describe gas exchange in the lungs and tissues

46. Mechanics of Breathing
Diaphragm contracts
expanding chest cavity
Membranous walls of lungs move outward along with chest walls
lowering pressure within lungs
Air rushes in through air passageways
until pressure in lungs equals atmospheric pressure

47. Mechanics of Breathing

48. Trachea Lung Diaphragm (a) Inhalation. (b) Exhalation.
Figure 45.8: Mechanics of breathing.
Changes in position of the diaphragm in exhalation and inhalation change the volume of the thoracic cavity.
Diaphragm
(a) Inhalation.
(b) Exhalation.
Fig. 45-8ab, p. 978

49. Diaphragm (c) Forced inhalation. (d) Forced exhalation.
Figure 45.8: Mechanics of breathing.
Changes in position of the diaphragm in exhalation and inhalation change the volume of the thoracic cavity.
Diaphragm
(c) Forced inhalation.
(d) Forced exhalation.
Fig. 45-8cd, p. 978

50. Respiratory Measurements
Tidal volume
amount of air moved into and out of lungs with each normal breath
Vital capacity
maximum volume exhaled after lungs fill to maximum extent
Residual capacity
air volume remaining in lungs at end of normal expiration

51. Regulation of Breathing
Respiratory centers in medulla and pons
regulate respiration
Chemoreceptors
sensitive to increase in CO2 concentration
stimulate respiratory centers
respond to increase in H+ or very low O2 concentration

52. Gas Exchange
O2 and CO2 exchange between alveoli and blood by diffusion
Pressure of a particular gas determines its direction and rate of diffusion

53. Partial Pressure Dalton’s law of partial pressures
in a mixture of gases, total pressure is the sum of the pressures of the individual gases
Each gas exerts a partial pressure
same pressure as if it were present alone
Partial pressure of atmospheric oxygen (Po2) is 160 mm Hg at sea level

54. Fick’s Law of Diffusion
The greater the difference in pressure on two sides of a membrane, and the larger the surface area, the faster the gas diffuses across the membrane

55. Gas Exchange in Lungs and Tissues

56. PO2 = 100 mm Hg PCO2 = 40 mm Hg Alveoli in lung O2 CO2 Capillary
in tissue
Capillary
in lung
Figure 45.9: Gas exchange in the lungs and tissues.
The concentration of oxygen is greater in the alveoli than in the pulmonary capillaries, so oxygen diffuses from the alveoli into the blood. Carbon dioxide is more concentrated in the blood than in the alveoli, so it diffuses out of the capillaries and into the alveoli. In the tissues, oxygen is more concentrated in the blood than in the body cells; it diffuses out of the capillaries into the cells. Carbon dioxide is more concentrated in the cells, so it diffuses out of the cells and moves into the blood. Note the differences in partial pressures of oxygen and carbon dioxide before and after gases are exchanged in the tissues.
Cells in body
PO2 = 40 mm Hg
PCO2 = 46 mm Hg
Fig. 45-9, p. 979

57. Insert “Respiratory cycle”
breathing_m.swf

58. See the breathing mechanisms in action by clicking on the figures in ThomsonNOW.

59. KEY CONCEPTS
In mammals, oxygen and carbon dioxide are exchanged between alveoli and blood by diffusion; the pressure of a particular gas determines its direction and rate of diffusion

60. Learning Objective 5
What is the role of hemoglobin in oxygen transport?
Identify factors that determine and influence the oxygen-hemoglobin dissociation curve

61. Hemoglobin Respiratory pigment in vertebrate blood
Almost 99% of oxygen in human blood is transported as oxyhemoglobin (HbO2)

62. Oxygen Measurement Oxygen-carrying capacity Oxygen content
maximum amount of oxygen that can be transported by hemoglobin
Oxygen content
actual amount of oxygen bound to hemoglobin
Percent O2 saturation
ratio of oxygen content to oxygen-carrying capacity
highest in pulmonary capillaries

63. Oxygen-Hemoglobin Dissociation Curve 1
As oxygen concentration increases, the amount of hemoglobin that combines with oxygen progressively increases
Affected by pH, temperature, CO2 concentration

64. Oxygen-Hemoglobin Dissociation Curve 2
Oxyhemoglobin dissociates more readily as CO2 concentration increases
CO2 combines with water and produces carbonic acid, which lowers pH
Bohr effect
displacement of oxygen-hemoglobin dissociation curve by change in pH

65. Oxygen-Hemoglobin Dissociation Curves

66. Oxygen-rich blood leaving the lungs Percent O2 saturation
Oxygen-poor blood returning from tissues
Figure 45.10: Oxygen–hemoglobin dissociation curves.
Partial pressure of oxygen (mm Hg)
Fig a, p. 980

67. Partial pressure of oxygen (mm Hg)
7.6
7.4
7.2
Percent O2 saturation
Figure 45.10: Oxygen–hemoglobin dissociation curves.
Partial pressure of oxygen (mm Hg)
Fig b, p. 980

68. Learning Objective 6
Summarize the mechanisms by which carbon dioxide is transported in the blood

69. CO2 Transport
About 60% of CO2 in blood is transported as bicarbonate ions
About 30% combines with hemoglobin
About 10% is dissolved in plasma

70. Buffer System 1
Carbon dioxide combines with water to form carbonic acid
catalyzed by carbonic anhydrase
Carbonic acid dissociates, forming
bicarbonate ions (HCO3-)
hydrogen ions (H+)

71. Buffer System 2 Hemoglobin combines with H+ Chloride shift
buffering the blood
Chloride shift
many bicarbonate ions diffuse into the plasma and are replaced by Cl-

72. CO2 Transport

73. Tissue cell CO2 Plasma Tissue CO2 capillary wall Red blood cell CO2
H2O
CO2 + H2O
CO2
Carbonic
anhydrase
Hemoglobin
Figure 45.11: Carbon dioxide transport.
H2CO3
Carbonic acid
H +
HCO3– + H+
Cl–
Bicarbonate
Chloride
shift
Cl–
HCO3–
Bicarbonate
Fig a, p. 981

74. Figure 45.11: Carbon dioxide transport.
Fig b, p. 981

75. Plasma HCO3– Bicarbonate Cl– Chloride shift HCO3– + H+ Bicarbonate Cl–
Carbonic acid
H +
Hemoglobin
CO2
CO2 + H2O
H2O
CO2
Pulmonary
capillary
wall
CO2
Figure 45.11: Carbon dioxide transport.
Alveoli
CO2
Fig b, p. 981

76. Carbonic anhydrase H2CO3 Carbonic acid HCO3– Bicarbonate
Plasma
Tissue
capillary
wall
Tissue cell
CO2
Red blood cell
CO2
H2O
CO2 + H2O
Carbonic
anhydrase
H2CO3
Carbonic acid
CO2
HCO3– + H+
Bicarbonate
Hemoglobin
H +
Figure 45.11: Carbon dioxide transport.
Cl–
Chloride
shift
HCO3–
Bicarbonate
Stepped Art
Fig a, p. 981

77. KEY CONCEPTS Respiratory pigments combine with oxygen and transport it
Almost all of the oxygen in vertebrate blood is transported as oxyhemoglobin; carbon dioxide is transported mainly as bicarbonate ions

78. Learning Objective 7
Describe the physiological effects of hyperventilation and of sudden decompression when a diver surfaces too quickly from deep water

79. Hyperventilation Reduces CO2 concentration in alveolar air and blood
A certain CO2 concentration in blood is needed to maintain normal blood pressure

80. Effects of Barometric Pressure
As altitude increases, barometric pressure falls, less oxygen enters the blood
hypoxia, loss of consciousness, death
Rapid decrease in barometric pressure can cause decompression sickness
among divers who ascend too rapidly

81. Diving Mammals Have high concentrations of myoglobin Diving reflex
pigment that stores oxygen in muscles
Diving reflex
group of physiological mechanisms
including decrease in metabolic rate
activated when a mammal dives to its limit

82. Diving Mammals

83. Learning Objective 8
Describe the defense mechanisms that protect the lungs
Describe the effects of polluted air on the respiratory system

84. Defense Mechanisms Ciliated mucous lining traps inhaled particles in
nose
pharynx
trachea
bronchi

85. Inhaling Polluted Air or Cigarette Smoke
Results in
bronchial constriction, increased mucus secretion, damage to ciliated cells, coughing
Can cause
chronic bronchitis, pulmonary emphysema, lung cancer

86. Effects of Cigarette Smoke