Transcript Chapt 22 Gas Exchange

Chapter 22
Gas Exchange
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• The process of gas exchange, often called
respiration
– Is the interchange of O2 and CO2
between an organism and its
environment
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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
CO2
Breathing
Lung
2
Circulatory
system
Transport
of gases by
the circulatory
system
Mitochondria
3
Figure 22.1
Exchange
of gases
with
body
cells
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CO2
Capillary
Cell
O2
• Gas exchange
– Provides O2 for cellular respiration and
removes its waste product, CO2
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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
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• 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
O2
Figure 22.2A
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Capillaries
• In most animals
–
Specialized body parts provide large
respiratory surfaces for gas exchange
Body surface
Body surface
Respiratory
surface
(gill)
CO2
Body cells
(no capillaries)
O2
CO2
Figure 22.2C
Capillary
O2
Body surface
Figure 22.2B
CO2
CO2
Figure 22.2D
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O2
Respiratory
surface
(air tubes)
Respiratory
surface
(within lung)
O2
Capillary
22.3 Gills are adapted for gas exchange in
aquatic environments
• Gills are extensions of the body
– That absorb O2 dissolved in water
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• In a fish, gas exchange
– Is enhanced by ventilation and the
countercurrent flow of water and blood
Gill arch
Oxygen-poor
blood
Direction
of water flow
Lamella
Oxygen-rich
blood
Gill arch
15%
Blood
vessels
% O2 in water
flowing over
lamellae % O in blood
2
flowing through capillaries
Gill
in lamellae
filaments
Figure 22.3
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Countercurrent exchange
22.4 The tracheal system of insects provides
direct exchange between the air and body cells
• Land animals
– Exchange gases by breathing air
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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)
Larynx
Left lung
Trachea
Right lung
Bronchus
Bronchiole
Diaphragm
Figure 22.5A
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(Heart)
• The bronchioles end in clusters of tiny sacs called
alveoli
–
Oxygen-rich
blood
Where gas exchange occurs
Oxygen-poor
blood
Alveoli
Blood
capillaries
Figure 22.5B, C
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Colorized SEM 6,200
Bronchiole
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
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• Smoking
–
Causes lung cancer, heart disease, and
emphysema
Lung
Heart
Figure 22.6
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22.7 Breathing ventilates the lungs
• Breathing
– Is the alternation of inhalation and
exhalation
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• 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
Figure 22.7A
Diaphragm contracts
(moves down)
Diaphragm relaxes
(moves up)
Inhalation
Exhalation
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• Vital capacity is the maximum volume of air we
can inhale and exhale
– But our lungs still hold a residual volume
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22.9 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
CO2 and O2
sensors in
aorta
Diaphragm
Figure 22.8
Rib muscles
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Nerve signals
indicating CO2
and O2 levels
• A drop in blood pH
– Triggers an increase in the rate and
depth of breathing
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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
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• Gas transport and exchange in the body
Inhaled air
Exhaled air
Alveolar
epithelial
cells
Air spaces
CO2
O2
Alveolar
capillaries of lung
CO2-rich,
O2-poor
blood
O2-rich,
CO2-poor
blood
Heart
Tissue
capillaries
CO2 Interstitial O2
fluid
Figure 22.9
Tissue cells
throughout body
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• Gases diffuse down partial-pressure gradients
– In the lungs and the tissues
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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
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• Most CO2 in the blood
CO2
Carbon
dioxide
–
Is transported as bicarbonate ions in the plasma
+
H2O
Water
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H2CO3
Carbonic
acid
H+
Hydrogen
ions
+
HCO3–
Bicarbonate
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
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• Fetal hemoglobin
– Enhances oxygen transfer from maternal
blood
• At birth, increasing CO2 in the fetal blood
– Stimulates the breathing control centers
to initiate breathing
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings