Download Ch 42 Gas exchange

Gas Exchange:
Respiration
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• Gas exchange occurs across specialized
respiratory surfaces
• Gas exchange
– Supplies oxygen for cellular respiration and
disposes of carbon dioxide
Respiratory
medium
(air of water)
O2
CO2
Respiratory
surface
Organismal
level
Circulatory system
Cellular level
Energy-rich
molecules
from food
Cellular respiration
Figure 42.19
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ATP
• Animals require large, moist respiratory
surfaces for the adequate diffusion of
respiratory gases
– Between their cells and the respiratory
medium, either air or water
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• In mammals, air inhaled through the nostrils
– Passes through the pharynx into the trachea,
bronchi, bronchioles, and dead-end alveoli,
where gas exchange occurs
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Gas exchange: occurs in alveoli of lungs,
diffusion of oxygen and carbon dioxide through
capillaries
• Ventilation: bringing in fresh air into the alveoli
(breathing)
• Cellular respiration: produces ATP for the cell,
uses oxygen and produces carbon dioxide.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Mammalian Respiratory Systems: A Closer Look
• A system of branching ducts
– Conveys air to the lungs
Branch
from the
pulmonary
artery
(oxygen-poor
blood)
Branch
from the
pulmonary
vein
(oxygen-rich
blood)
Terminal
bronchiole
Nasal
cavity
Pharynx
Left
lung
Alveoli
50 µm
50 µm
Larynx
Esophagus
Trachea
Right lung
Bronchus
Bronchiole
Diaphragm
SEM
Heart
Figure 42.23
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Colorized SEM
Alveoli
• Very small but huge in numbers (large surface
area for gas exchange)
• Made up of a single layer of thin cells
• Covered by a dense network of blood
capillaries
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How a Mammal Breathes
• Mammals ventilate their lungs by breathing
– By negative pressure breathing, which pulls air
into the lungs
Rib cage
expands as
rib muscles
contract
Air inhaled
Rib cage gets
smaller as
rib muscles
relax
Air exhaled
Lung
Diaphragm
INHALATION
Diaphragm contracts
(moves down)
Figure 42.24
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EXHALATION
Diaphragm relaxes
(moves up)
Inhalation:
• External intercostal muscles contract (moves
rib cage up and out)
• Diaphragm contracts
• Increase in volume, drop in pressure (below
atmospheric pressure)
• Air flows into lungs until pressure inside lungs
rises to atmospheric pressure.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Exhalation
• Internal intercostal muscles contract (moves rib
cage down and in)
• Abdominal muscles contract, pushing up
diaphragm
• Decrease in volume, pressure rises above
atmospheric pressure
• Air flows out of lungs until the pressure in lungs
falls back to atmospheric pressure.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Why do we need a ventilation system???
• Maintain the concentration gradients of gases
(oxygen/carbon dioxide) in the alveoli.
– Carbon dioxide needs to be low in alveoli so it moves
into the alveoli from capillaries.
– Oxygen needs to be high in alveoli so it can move into
capillaries.
– Ventilation makes this possible by getting rid of carbon
dioxide and bringing in oxygen
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The Role of Partial Pressure Gradients
• Gases diffuse down pressure gradients
– In the lungs and other organs
• Diffusion of a gas
– Depends on differences in a quantity called
partial pressure
• A gas always diffuses from a region of higher
partial pressure
– To a region of lower partial pressure
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• In the lungs and in the tissues
– O2 and CO2 diffuse from where their partial
pressures are higher to where they are lower
– RESPIRATION
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Inhaled air
Exhaled air
160 0.2
O2 CO2
120 27
Alveolar spaces
O2 CO2
104
Alveolar
epithelial
cells
40
O2 CO2
Blood
entering
alveolar
capillaries
40
O2
CO2
2
1
O2
Alveolar
capillaries
of lung
45
O2 CO2
104
Pulmonary
veins
Systemic
arteries
Systemic
veins
CO2
40
40
O2 CO2
Pulmonary
arteries
Blood
leaving
tissue
capillaries
Blood
leaving
alveolar
capillaries
Heart
Tissue
capillaries
O2
3
4
45
O2
CO2
Tissue
cells
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100
40
O2 CO2
O2 CO2
Figure 42.27
Blood
entering
tissue
capillaries
<40 >45
O2 CO2
Respiratory Pigments
• Respiratory pigments
– Are proteins that transport oxygen
• Greatly increase the amount of oxygen that
blood can carry
• The respiratory pigment of almost all
vertebrates
– Is the protein hemoglobin, contained in the
erythrocytes
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• Like all respiratory pigments
– Hemoglobin must reversibly bind O2, loading
O2 in the lungs and unloading it in other parts
of the body
Heme group
Iron atom
O2 loaded
in lungs
O2 unloaded
In tissues
Figure 42.28
Polypeptide chain
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
O2
O2