1. Chapter 22
Gas Exchange

2. Surviving in Thin Air The high mountains of the Himalayas
Surviving in Thin Air
The high mountains of the Himalayas
Have claimed the lives of even the world’s top mountain climbers
The air at the height of the world’s highest peak, Mt. Everest
Is so low in oxygen that most people would pass out instantly if exposed to it

3. Twice a year, flocks of geese migrate over the Himalayas
They are able to fly at such a high altitude because of the efficiency of their lungs
These birds have blood with hemoglobin with a very high affinity for oxygen
This adaptation allows them to carry large amounts of oxygen to their tissues to exchange with carbon dioxide

4. The process of gas exchange, often called respiration
Is the interchange of O2 and CO2 between an organism and its environment

5. MECHANISMS OF GAS EXCHANGE
Overview: Gas exchange involves:
breathing,
transport of gases, and
exchange of gases with tissue cells 1
Breathing O2
CO2
Lung
Circulatory
system 2
Transport
of gases by
the circulatory 3
Exchange
of gases
with
body
cells
Capillary
Cell
Mitochondria
The three phases of gas exchange
Figure 22.1

6. Animals exchange O2 and CO2 across moist body surfaces
Respiratory surfaces
Must be thin and moist for diffusion of O2 and CO2 to occur

7. Some animals, like the earthworm
Some animals, like the earthworm
Use their entire skin as a gas-exchange organ
Cut
Cross section
of respiratory
surface (the
skin covering
the body)
CO2
Capillaries O2
Figure 22.2A

8. In most animals
Specialized body parts provide large respiratory surfaces for gas exchange
Body surface
Respiratory
surface
(air tubes)
Body cells
(no capillaries) O2
CO2
Body surface
Respiratory
surface
(gill)
Capillary
CO2 O2
Figure 22.2C
Body surface
Respiratory
surface
(within lung)
Capillary
CO2 O2
Figure 22.2B
Figure 22.2D

9. Gills are adapted for gas exchange in aquatic environments
Gills are extensions of the body
That absorb O2 dissolved in water
Figure 42.20b
(b) Marine worm. Many polychaetes (marine worms of the phylum Annelida) have a pair of flattened appendages called parapodia on each body segment. The parapodia serve as gills and also function in crawling and swimming.

10. In a fish, gas exchange is facilitated by feathery gills
Figure 42.1

11. In a fish, gas exchange
Is enhanced by ventilation and the countercurrent flow of water and blood
Gill arch
Direction
of water flow
Blood
vessels
Gill
filaments
Oxygen-rich
blood
Oxygen-poor
Lamella
15%
40%
70%
100%
60%
80%
30% 5%
% O2 in water
flowing over
lamellae
% O2 in blood
flowing through capillaries
in lamellae
Countercurrent exchange
Figure 22.3

12. The tracheal system of insects
--provides direct exchange between the air and body cells
--Transport O2 directly to body cells through a network of finely branched tubes
Air sacs
Tracheae
Opening
for air
LM 250
Body
cell
Tracheole
Air
sac
Trachea
Body wall
CO2 O2
Figure 22.4A, B

13. Terrestrial vertebrates have lungs
(Heart)
Diaphragm
Bronchiole
Bronchus
Right lung
Trachea
Larynx
(Esophagus)
Pharynx
Nasal
cavity
Left lung
In mammals, air inhaled through the nostrils
Passes through the pharynx and larynx into the trachea, bronchi, and bronchioles
Figure 22.5A

14. The human respiratory system

15. The Nasal Cavity
Olfactory receptors are located in the mucosa on the superior surface
The rest of the cavity is lined with respiratory mucosa
Moistens air
Traps incoming foreign particles
Slide 13.4a

16. Trachea (Windpipe) Connects larynx with bronchi
Lined with ciliated mucosa
Beat continuously in the opposite direction of incoming air
Expel mucus loaded with dust and other debris away from lungs
Walls are reinforced with C-shaped cartilage

17. Coverings of the Lungs
Pulmonary (visceral) pleura covers the lung surface
Parietal pleura lines the walls of the thoracic cavity
Pleural fluid fills the area between layers of pleura to allow gliding

18. Respiratory Membrane (Air-Blood Barrier)
Thin squamous epithelial layer lining alveolar walls
Pulmonary capillaries cover external surfaces of alveoli

19. The bronchioles end in clusters of tiny sacs called alveoli
The bronchioles end in clusters of tiny sacs called alveoli
Where gas exchange occurs
Colorized SEM 6,200
Oxygen-rich
blood
Bronchiole
Oxygen-poor
Alveoli
Blood
capillaries
Figure 22.5B, C

20. Respiratory Membrane (Air-Blood Barrier)

21. Gas Exchange Gas crosses the respiratory membrane by diffusion
Oxygen enters the blood
Carbon dioxide enters the alveoli
Macrophages add protection
Surfactant coats gas-exposed alveolar surfaces

22. Breathing ventilates the lungs
Is the alternation of inhalation and exhalation

23. The contraction of rib muscles and the diaphragm
Rib cage
expands as
rib muscles
contract
Air
inhaled
Rib cage gets
smaller as
relax
exhaled
Lung
Diaphragm
Diaphragm relaxes
(moves up)
Diaphragm contracts
(moves down)
Inhalation
Exhalation
Expands the chest cavity and
reduces air pressure in the alveoli (negative pressure breathing)
Figure 22.7A

24. Inspiration Diaphragm and intercostal muscles contract
The size of the thoracic cavity increases
External air is pulled into the lungs due to an increase in intrapulmonary volume
Slide 13.22a

25. Exhalation
Largely a passive process which depends on natural lung elasticity
As muscles relax, air is pushed out of the lungs
Forced expiration can occur mostly by contracting internal intercostal muscles to depress the rib cage
Slide 13.23a

26. The pleural cavity is maintained at a negative pressure compared to the atmosphere
The thin liquid film between the chest wall and lungs, keeps the lungs from being pulled away from the chest wall. Because of inward elastic force of the lungs and the outward elastic forces of the chest wall, the pressure between the lungs and the chest wall is negative.

27. Pressure differences between pleural fluid and lung

28. the pressure between the two glass slides is negative
The lungs are like the lower slide being pulled with a fixed rubber band. The chest wall is like the upper slide with a handle. There is liquid between the chest wall and lungs. This liquid, which is in a thin film-like form, keeps the two together. The inward elastic force in the lungs works towards decreasing the lung volume (Note that the rubber bands in the lungs are lightly stretched).
The outward elastic force of the chest wall increases the volumes of the thoracic cavity and of the lungs. The pressure between the lungs and chest wall (pleural pressure) is negative (note that the blue pressure gauge, with its tip between the lung and chest wall, is elevated on the lung side, compared to the outer-side, which is opened and thus indicates the atmospheric pressure).

29. Pressure changes during breathing
Inspiratory muscles, such as the diaphragm, contract, increasing the volume of the thoracic cavity. Because of the thin liquid film, the lung volume is also increased. Since this is in the opposite direction of the lung elasticity (note that the 'rubber bands' are further stretched), the pleural pressure becomes more negative (note the blue pressure gauge). This is similar to: A rubber band is attached to a desk and the lower glass slide. With water in between, when the upper glass slide is lifted, pulling the rubber band lightly, the negative pressure inbetween is small, but when the rubber band is pulled strongly, the negative pressure inbetween is large. Inspiration is like the latter situation.

30. Pressure Differences in the Thoracic Cavity
Normal pressure within the pleural space is always negative (intrapleural pressure)
Differences in lung and pleural space pressures keep lungs from collapsing --due to elastic tissues in the lung and surface tension in the alveoli.
Slide 13.24

31. What happens if the pleural membrane is punctured?
When the pleural membrane is punctured, atmospheric air rushes into the pleural cavity,
and the intrapleural pressure immediately changes from -4 mm Hg to 0 mm Hg (760mmHg).
The negative pressure that holds the lung open is now eliminated, and the stretched lung collapses due to its elasticity and surface tension.
If the lung collapses, it can no longer be, inflated by inhalation, even when the diaphragm and ribs can still carry out normal breathing movements.

32. Micconception:
“When one is shot in the lung, he couldn’t breathe because the lungs would collapse.”
The fact is:
When one is shot in one side of the two lungs, provided that the other side of the thoracic cage and pleural membranes are intact, he could still breathe with ONE side of his lung—which wouldn’t collapse because the two sides of the lungs are separately wrapped with pleural membranes.

33. Nonrespiratory Air Movements
Can be caused by reflexes or voluntary actions
Examples
Cough and sneeze – clears lungs of debris
Laughing
Crying
Yawn
Hiccup
Slide 13.25

34. Respiratory Volumes and Capacities
Normal breathing moves about 500 ml of air with each breath (tidal volume [TV])
Many factors that affect respiratory capacity
A person’s size
Sex
Age
Physical condition
Residual volume of air – after exhalation, about 1200 ml of air remains in the lungs
Slide 13.26

35. Respiratory Volumes and Capacities
Inspiratory reserve volume (IRV)
Amount of air that can be taken in forcibly over the tidal volume
Usually between 2100 and 3200 ml
Expiratory reserve volume (ERV)
Amount of air that can be forcibly exhaled
Approximately 1200 ml
Slide 13.27a

36. Respiratory Volumes and Capacities
Residual volume
Air remaining in lung after expiration
About 1200 ml
Slide 13.27b

37. Respiratory Volumes and Capacities
Vital capacity
The total amount of exchangeable air
Vital capacity = TV + IRV + ERV
Dead space volume
Air that remains in conducting zone and never reaches alveoli – is therefore NOT involved in gas exchange
About 150 ml
Slide 13.28

38. Respiratory Volumes and Capacities
Functional volume
Air that actually reaches the respiratory zone
Usually about 350 ml
Respiratory capacities are measured with a spirometer
Functional volume + Dead space volume = Tidal volume
Slide 13.29

39. Respiratory Capacities
Figure 13.9
Slide 13.30

40. Vital capacity is the maximum volume of air we can inhale and exhale
But our lungs still hold a residual volume

41. Misconception: Dead space = residual volume
The dead space, with a volume of about 150 ml, comprises the air passage in the nose, pharynx, trachea, bronchi and bronchioles, where no gas exchange can occur.
The residual volume refers to the volume of air remaining in the lungs after exhalation and is approximately 2500 ml during quiet breathing and 1200 ml after a maximal active exhalation.

42. Misconception:
“Inhaled air fills alveoli and gas exchange takes place between the inhaled atmosphere air and the blood capillary directly.”
The efficiency of ventilation is higher when a person breathes rapidly and shallowly compared to when he breathes slowly and deeply
Of the 500 ml of fresh air taken into the breathing system in each breath, due to the presence of the dead space, only about 350 ml reach the alveoli for gas exchange.
Moreover, the relatively large proportion of residual air to tidal air further reduces the efficiency of gas exchange inside the alveoli.
As the residual air is in direct contact with the alveolar membrane, the oxygen in the tidal air has to diffuse for some distance before reaching the gas exchange surface and entering into the blood (Fig. 16). This process again reduces the efficiency of the body in extracting oxygen from the tidal air.

43. Air sacs empty; lungs fill
Air flows in one direction
Through the more efficient lungs of birds (reference only)
Air
Anterior
air sacs
Posterior
Trachea
Lungs
tubes
in lung
1 mm
Exhalation:
Air sacs empty; lungs fill
Inhalation:
Air sacs fill
Figure 22.7B

44. Breathing is automatically controlled
Brain
Cerebrospinal
fluid
Pons
Medulla
Nerve signals
trigger
contraction
of muscles
Breathing
control
centers
stimulated by:
CO2 increase /
pH decrease
in blood
indicating CO2
and O2 levels
CO2 and O2
sensors in
aorta
Diaphragm
Rib muscles
Breathing control centers in the brain
Keep breathing in tune with body needs,
sensing and responding to the CO2 level in the blood

45. Neural Regulation of Respiration
Activity of respiratory muscles is transmitted to the brain by the nerves
Neural centers that control rate and depth are located in the medulla
Normal respiratory rate (eupnea) is 12–15 respirations per minute
Hypernia is increased respiratory rate often due to extra oxygen needs

46. Factors Influencing Respiratory Rate and Depth
Physical factors
Increased body temperature
Exercise
Talking
Coughing
Volition (conscious control)
Emotional factors

47. Factors Influencing Respiratory Rate and Depth
Chemical factors
Carbon dioxide levels
Level of carbon dioxide in the blood is the main regulatory chemical for respiration
Increased carbon dioxide increases respiration
Changes in carbon dioxide act directly on the medulla oblongata

48. Factors Influencing Respiratory Rate and Depth
Chemical factors (continued)
Oxygen levels
Changes in oxygen concentration in the blood are detected by chemoreceptors in the aorta and carotid artery
Information is sent to the medulla oblongata

49. Total amount of CO2 produced =
Miconception
During vigorous exercise, exhaled air contains a higher conc. of carbon dioxide and a lower concentration of oxygen than that produced at rest.
During vigorous exercise, ventilation can increase from the resting level of about 8 litres per minute to well over 90 litres per minute through an increase in rate and depth of breathing.
The increase in ventilation is so remarkable that, except in the most exhaustive type of exercise, CO2 is exhaled as fast as it is produced by the active tissues. So the concentration of CO2 is relatively constant regardless of activity.
Total amount of CO2 produced =
Ventilation rate X CO2 concentration in arterial blood / CO2 concentration in exhaled air during exercise
As the total amount of CO2 produced increases rapidly during exercise, it is removed immediately by a corresponding increase in the rate and depth of breathing which leads to a much greater ventilation rate. Thus the concentration of CO2 in the arterial blood or exhaled air remains rather constant (Vander et. al., 1994.)

50. Fig 17 The effects of exercise on ventilation rate, and conc
Fig 17 The effects of exercise on ventilation rate, and conc. of oxygen and carbon dioxide in blood
Despite the extremely rapid production of CO2 during exercise and the simultaneous consumption of. O2, ventilation increases so greatly that this prevents the blood concentration of these gases from changing significantly from normal.
There is even a drop in blood CO2 level during maximal activity. Therefore, most physiologists believe that the increase in ventilation during exercise is NOT caused by changes in the level of either or both of these two respiratory gases.

51. Misconception
“During exercise, the production of a large amount of CO2 causes a build-up of CO2 in the blood that stimulates the respiratory centre.”
As shown in Fig. 17, there is no increase in CO2 concentration in the arterial blood during vigorous exercise.
Therefore, the increase in ventilation rate during exercise cannot be mediated through the stimulation of the respiratory centre by a higher CO2 level in blood.
Evidences that a neural mechanism is involved:
When the venous levels of C02, 02 and pH of a person are artificially maintained at resting levels, muscular activity results in a marked increase in ventilation.
Passive ‘pumping’ of the limbs to excite these stretch receptors also increases the ventilation rate. These findings suggest that the increase in ventilation is caused by impulses reaching the respiratory centre from the stretch receptors (proprioceptors) in contracting skeletal muscles.
When the cerebral cortex sends impulses to the contracting muscles, it is also sending parallel signals to the respiratory centre at the same time to increase the rate and depth of breathing. This is similar to the role of the cerebral cortex in increasing the cardiac output during exercise. Consequently, the respiratory and circulatory adjustments to exercise are well integrated through these higher levels of the nervous system.

52. TRANSPORT OF GASES IN THE BODY
Blood transports respiratory gases
The heart pumps oxygen-poor blood to the lungs
Where it picks up O2 and drops off CO2
Then the heart pumps the oxygen-rich blood to body cells
Where it drops off O2 and picks up CO2
Exhaled air
Inhaled air
Air spaces
Alveolar
epithelial
cells
CO2 O2
CO2-rich,
O2-poor
blood
O2-rich,
CO2-poor
Heart
Tissue
capillaries
Interstitial
fluid
Tissue cells
throughout body
capillaries of lung

53. 22.10 Hemoglobin carries O2 and helps transport CO2 and buffer the blood
Iron atom
Heme group
O2 loaded
in lungs
O2 unloaded
in tissues
Polypeptide chain
Most CO2 in the blood
--Is transported as bicarbonate ions in the plasma
CO2 +
H2O
H2CO3 H+
HCO3–
Carbon
dioxide
Water
Carbonic
acid
Hydrogen
ions
Bicarbonate

54. Exchange of gases between blood and body cells

55. Hemoglobin also helps transport CO2
Figure 42.30
Tissue cell
CO2
Interstitial fluid
CO2 produced
CO2 transport from tissues
Blood plasma within capillary
Capillary wall
H2O
Red blood cell Hb
Carbonic acid
H2CO3
HCO3– H+ +
Bicarbonate
Hemoglobin picks up CO2 and H+
Hemoglobin releases CO2 and H+
CO2 transport to lungs
Alveolar space in lung 2 1 3 4 5 6 7 8 9 10 11
To lungs
Carbon dioxide produced by body tissues diffuses into the interstitial fluid and the plasma.
Over 90% of the CO2 diffuses into red blood cells, leaving only 7% in the plasma as dissolved CO2.
Some CO2 is picked up and transported by hemoglobin.
However, most CO2 reacts with water in red blood cells, forming carbonic acid (H2CO3), a reaction catalyzed by carbonic anhydrase contained. Within red blood cells.
Carbonic acid dissociates into a biocarbonate ion (HCO3–) and a hydrogen ion (H+).
Hemoglobin binds most of the H+ from H2CO3 preventing the H+ from acidifying the blood and thus preventing the Bohr shift.
CO2 diffuses into the alveolar space, from which it is expelled during exhalation. The reduction of CO2 concentration in the plasma drives the breakdown of H2CO3
Into CO2 and water in the red blood cells (see step 9), a reversal of the reaction that occurs in the tissues (see step 4).
Most of the HCO3– diffuse into the plasma where it is carried in the bloodstream to the lungs.
In the HCO3– diffuse from the plasma red blood cells, combining with H+ released from hemoglobin and forming H2CO3.
Carbonic acid is converted back into CO2 and water.
CO2 formed from H2CO3 is unloaded from hemoglobin and diffuses into the interstitial fluid.

56. CONNECTION
22.11 The human fetus exchanges gases with the mother’s bloodstream
Placenta, containing
maternal blood vessels
and fetal capillaries
Umbilical cord,
containing fetal
blood vessels
Amniotic
fluid
Uterus
A human fetus
Exchanges gases with maternal blood in the placenta
Figure 22.11

57. Fetal hemoglobin
Enhances oxygen transfer from maternal blood
At birth, increasing CO2 in the fetal blood
Stimulates the breathing control centers to initiate breathing

58. Smoking is a deadly assaults on our respiratory system
CONNECTION
Smoking is a deadly assaults on our respiratory system
Mucus and cilia in the respiratory passages
Protect the lungs
Can be destroyed by smoking

59. Causes lung cancer, heart disease, and emphysema
Smoking
Causes lung cancer, heart disease, and emphysema
Lung
Heart
Figure 22.6

60. Respiratory Disorders: Chronic Obstructive Pulmonary Disease (COPD)
Exemplified by chronic bronchitis and emphysema
Major causes of death and disability in the United States

61. Respiratory Disorders: Chronic Obstructive Pulmonary Disease (COPD) --reference
Features of these diseases
Patients almost always have a history of smoking
Labored breathing (dyspnea) becomes progressively more severe
Coughing and frequent pulmonary infections are common

62. Respiratory Disorders: Chronic Obstructive Pulmonary Disease (COPD)
Features of these diseases (continued)
Most victimes retain carbon dioxide, are hypoxic and have respiratory acidosis
Those infected will ultimately develop respiratory failure

63. Emphysema Alveoli enlarge as adjacent chambers break through
Chronic inflammation promotes lung fibrosis
Airways collapse during expiration
Patients use a large amount of energy to exhale
Overinflation of the lungs leads to a permanently expanded barrel chest
Cyanosis appears late in the disease

64. Chronic Bronchitis
Mucosa of the lower respiratory passages becomes severely inflamed
Mucus production increases
Pooled mucus impairs ventilation and gas exchange
Risk of lung infection increases
Pneumonia is common
Hypoxia and cyanosis occur early

65. Chronic Obstructive Pulmonary Disease (COPD) --reference
Figure 13.13

66. Lung Cancer Accounts for 1/3 of all cancer deaths in the United States
Increased incidence associated with smoking

67. Sudden Infant Death syndrome (SIDS)
Apparently healthy infant stops breathing and dies during sleep
Some cases are thought to be a problem of the neural respiratory control center
One third of cases appear to be due to heart rhythm abnormalities

68. Asthma Chronic inflamed hypersensitive bronchiole passages
Response to irritants with dyspnea*, coughing, and wheezing
Dyspnea--Difficult or laboured respiration

69. Developmental Aspects of the Respiratory System (reference)
Lungs are filled with fluid in the fetus
Lungs are not fully inflated with air until two weeks after birth
Surfactant that lowers alveolar surface tension is not present until late in fetal development and may not be present in premature babies

70. Developmental Aspects of the Respiratory System
Important birth defect
Cystic fibrosis – oversecretion of thick mucus clogs the respiratory system

71. Respiratory Rate Changes Throughout Life
Newborns – 40 to 80 respirations per minute
Infants – 30 respirations per minute
Age 5 – 25 respirations per minute
Adults – 12 to 18 respirations per minute
Rate often increases somewhat with old age

72. Aging Effects (reference)
Elasticity of lungs decreases
Vital capacity decreases
Blood oxygen levels decrease
Stimulating effects of carbon dioxide decreases
More risks of respiratory tract infection