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
Your body will not increase in the affinity of hemoglobin for oxygen.  

3. Twice a year, flocks of geese migrate over the Himalayas
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
Birds do not have mitochondria that are more efficient than those of other vertebrates.  

4. The process of gas exchange, often called respiration
Is the interchange of O2 and CO2 between an organism and its environment
Animals need oxygen because without it, animals cannot obtain enough energy from their food.

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

6. Gas exchange provides O2 for cellular respiration and removes its waste product, CO2
The process of moving air in and out of the lungs is called breathing.
When blood passes by body cells, the body cells take up oxygen and release carbon dioxide to the blood.

7. 22.2 Animals exchange O2 and CO2 across moist body surfaces
22.2 Animals exchange O2 and CO2 across moist body surfaces
Respiratory surfaces must be thin and moist for diffusion of O2 and CO2 to occur
The part of an animal where gas exchange occurs is called the respiratory surface.  
Animals that use their body surface for gas exchange must have a high ratio of body surface area to volume.

8. 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

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

10. 22.3 Gills are adapted for gas exchange in aquatic environments
22.3 Gills are adapted for gas exchange in aquatic environments
Gills are extensions of the body that absorb O2 dissolved in water
Gills are generally unsuitable for animals living on land because the animals would lose too much water.  
The chief advantage of exchanging gases in water is that no energy need be expended to keep the exchange surface wet.

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

12. 22.4 The tracheal system of insects provides direct exchange between the air and body cells
Land animals
Exchange gases by breathing air

13. Tracheal systems in insects
Tracheal systems in insects
Transport O2 directly to body cells through a network of finely branched tubes
Air sacs
Tracheae
Opening
for air
Body
cell
Air
sac
Tracheole
LM 250
Trachea O2
CO2
Body wall
Figure 22.4A, B

14. 22.5 Terrestrial vertebrates have lungs
22.5 Terrestrial vertebrates have lungs
In mammals, air inhaled through the nostrils
Passes through the pharynx and larynx into the trachea, bronchi, and bronchioles
Nasal
cavity
Pharynx
(Esophagus)
Left lung
Larynx
Trachea
Right lung
Bronchus
Bronchiole
Diaphragm
Figure 22.5A
(Heart)

15. The nasal cavities in humans is used for:
humidification of inhaled air  
warming of inhaled air  
filtering of inhaled air  
sampling of inhaled air for odors  

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

17. 22.6 Smoking is a deadly assaults on our respiratory system
CONNECTION
22.6 Smoking is a deadly assaults on our respiratory system
Mucus and cilia in the respiratory passages
Protect the lungs
Can be destroyed by smoking causing coughing.

18. Smoking causes lung cancer, heart disease, and emphysema & reduces the lungs’ capacity for gas exchange.
Lung
Heart
Figure 22.6

19. 22.7 Breathing ventilates the lungs
22.7 Breathing ventilates the lungs
Breathing is the alternation of inhalation and exhalation
Inhalation in humans is achieved by  contraction of the diaphragm and chest muscles.  
Exhalation results mainly from the relaxation of the chest muscles and diaphragm.  

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

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

22. Air sacs empty; lungs fill
Air flows in one direction through the more efficient lungs of birds
The function of air sacs in birds is to permit one-way ventilation of the lungs.
Anterior
air sacs
Air
Air
Posterior
air sacs
Trachea
Lungs
Air
tubes
in lung
Inhalation:
Air sacs fill
Exhalation:
Air sacs empty; lungs fill
1 mm
Figure 22.7B

23. 22.8 Breathing is automatically controlled
22.8 Breathing is automatically controlled
Breathing control centers in the brain
Keep breathing in tune with body needs, sensing and responding to the CO2 level in the blood
Brain
Cerebrospinal
fluid
Pons
Medulla
Breathing
control
centers
stimulated by:
Nerve signals
trigger
contraction
of muscles
CO2 increase /
pH decrease
in blood
Nerve signals
indicating CO2
and O2 levels
CO2 and O2
sensors in
aorta
Diaphragm
Figure 22.8
Rib muscles

24. A drop in blood pH
Triggers an increase in the rate and depth of breathing

25. TRANSPORT OF GASES IN THE BODY
22.9 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

26. Gas transport and exchange in the body
Gas transport and exchange in the body
Exhaled air
Inhaled air
Alveolar
epithelial
cells
Air spaces
CO2 O2
CO2 O2
Alveolar
capillaries of lung
CO2-rich,
O2-poor
blood
O2-rich,
CO2-poor
blood
Heart
Tissue
capillaries
CO2 O2
CO2
Interstitial
fluid O2
Figure 22.9
Tissue cells
throughout body

27. Gases diffuse down partial-pressure gradients
In the lungs and the tissues

28. 22.10 Hemoglobin carries O2 and helps transport CO2 and buffer the blood
Hemoglobin in red blood cells
Transports oxygen, helps buffer the blood, and carries some CO2
Iron atom
O2 loaded
in lungs
O2 unloaded
in tissues
Heme group
Figure 22.10
Polypeptide chain

29. Most CO2 in the blood Is transported as bicarbonate ions in the plasma
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

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

31. Fetal hemoglobin
Enhances oxygen transfer from maternal blood
At birth, increasing CO2 in the fetal blood causes the baby to start breathing.