Transcript Chap 22 – Gas Exchange

Chapter 22
Gas Exchange
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
© 2012 Pearson Education, Inc.
Lecture by Edward J. Zalisko
Gas Exchange - Function of the Respiratory
System
 Gas exchange (respiration), the interchange of
– O2 and CO2
– O2 is substrate for cellular respiration (ATP generation).
– CO2 waste product from cell respiration
C6H12O6 + O2 -----> CO2 + H2O + ATP
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O2
3 Stages of Gas
Exchange
CO2
1
Lung
Heart
1. breathing,
Blood
vessels
2. transport of
oxygen and
carbon dioxide
in blood, and
2
3. exchange of
gases with
body cells.
– Body tissues
take up
oxygen and
– release
carbon
dioxide.
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Breathing
Transport
of gases by
the circulatory
system
Capillary
3
Exchange of
gases with
body cells
Circulatory
System
Mitochondria
O2
CO2
Cell
Universal Rules of Gas Exchange
 Gas exchange is occurs by simple diffusion
of gases across cell membranes
 Respiratory surfaces must be moist
 Respiratory surfaces must be thin
– Optimize SA:volume
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Gas Exchange in Air vs. Water
 Aquatic:
– Disadvantage:
– Water holds only about 3% of the oxygen in air.
– Cold water holds more oxygen than warm water.
– Water move difficult to move across respiratory
surfaces.
– Advantage:
– Respiratory surfaces remain moist - can be directly
exposed to water environment
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Gas Exchange in Air vs. Water
 Land:
– Advantage:
– Concentration of O2 much higher in air
– Air requires less energy to move over respiratory surfaces.
– Disadvantage:
– Respiratory surfaces more likely to dry out
 Land organisms use internal respiratory systems
(lungs, trachea, etc.)
 Plants regulate stomata opening using guard cells
to prevent water loss by transpiration.
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Small organisms have sufficient
SA:volume ratio that they do not
require a specialized respiratory
system.
Diffusion
Mouth
Gastrovascular
cavity
Diffusion
Diffusion
Single cell
Two cell layers
Gas Exchange Structures in Various Organisms
 Organisms have specialized body parts for
gas exchange:
– Skin in earthworms
– gills in fish
– Lungs and skin in amphibians,
– tracheal systems in arthropods
– Plants use stomata
– lungs in tetrapods that live on land, such as
– amphibians, reptiles, birds, mammals
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Cross section of the
respiratory surface
(the outer skin)
CO2
O2
Capillaries
Body surface
Respiratory
surface
(gills)
CO2
O2
Capillary
Figure 22.3
Oxygen-poor
blood
Oxygen-rich
blood
Water
flow
Lamella
Blood vessels
Operculum
(gill cover)
Gill arch
Water flow
between
lamellae
Blood flow through
capillaries in a lamella
Countercurrent exchange
Water flow, showing % O2
Gill filaments
Diffusion
of O2 from
water
to blood
100
70
40
15
80
60
30
5
Blood flow in simplified
capillary, showing % O2
Body surface
Tracheae
Air sacs
O2
CO2
Tracheoles
Opening
for air
Body
cell
Tracheole
Air
sac
Trachea
Body wall
O2
CO2
Respiratory
surface
(tips of tracheae
Body cells
(no capillaries)
Figure 22.2D
Body surface
CO2
CO2
Respiratory
surface
(within lung)
O2
O2
Capillary
CO2
O2
Light
H2O
Sugar
O2
H2O
and minerals
CO2
Plants Gas exchange thru
leaves
Eudicot leaf
Vein
Cuticle
Upper
epidermis
Xylem
Phloem
Mesophyll
Guard
cells
Lower
epidermis
Stoma
Sheath
Key
Stoma = site of CO2 / O2
exchange
Dermal tissue system
Ground tissue system
Vascular tissue system
Guard cells of stomates CLOSE when too much water is
lost.
When water is plentiful, guard cells actively transport K+
INTO cell, water follows, and stoma open.
Guard cells
H2O
H2O
H2O
H2O
H2O
K
Vacuole
H2O
H2O
H2O
H2O
Stoma
H2O
Stoma opening
Stoma closing
THE HUMAN RESPIRATORY
SYSTEM
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To the
heart
Nasal cavity
Left lung
Pharynx
(Esophagus)
Oxygen-rich
blood
From the
heart
Oxygen-poor
blood
Bronchiole
Larynx
Trachea
CO2
O2
Right lung
Bronchus
Bronchiole
Alveoli
Blood
capillaries
Diaphragm
(Heart)
Alveoli are well adapted for gas exchange with high surface areas of
capillaries.
– O2
diffuses into the blood and
– CO2 diffuses out of the blood.
Alveoli are site of
gas exchange in
lungs!
Animation: CO2 from Blood to Lungs
Animation: CO2 from Tissues to Blood
Animation: O2 from Blood to Tissues
Animation: O2 from Lungs to Blood
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Gas Exchange
occurs by
passive
diffusion!!!
Gasses diffuse
towards regions
of lowest partial
pressure.
(Partial pressure
= measure of
concentration of
gas dissolved in
liquid)
CO2 in exhaled air
O2 in inhaled air
Alveolar
epithelial
cells
Air spaces
CO2
O2
Alveolar
capillaries
of lung
CO2-rich,
O2-poor
blood
O2-rich,
CO2-poor
blood
Tissue
capillaries
CO2
Interstitial
fluid
Heart
O2
Tissue cells
throughout the body
Figure 22.10_1
[CO2]
LOWEST in
alveoli and
tissue
capillaries
Alveolar
capillaries
of lung
CO2-rich,
O2-poor
blood
[CO2]
HIGHEST in
tissues and
blood
arriving to
lung from
tissues
[O2]
LOWEST in
blood at
tissues and
in blood
arriving at
O2-rich, lung
CO2-poor
blood
Tissue
capillaries
Heart
[O2]
HIGHEST in
alveoli and
blood
arriving TO
tissues
Blood transports respiratory gases
 Gases move from areas of higher concentration to
areas of lower concentration.
– Gases in the alveoli of the lungs have more O2 and less
CO2 than gases in the blood.
– O2 moves from the alveoli of the lungs into the blood.
– CO2 moves from the blood into the alveoli of the lungs.
– The tissues have more CO2 and less O2 than gases in the
blood.
– CO2 moves from the tissues into the blood.
– O2 moves from the blood into the tissues.
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Hemoglobin carries O2 in the blood
Iron atom
O2 loaded
in lungs
O2
O2 unloaded
in tissues
Heme group
Polypeptide chain
Hemoglobin:
4 subunits: 2 , 2 
2o structure: all -helical protein
Contains heme coenzyme with iron cofactor at center
Fe cofactor directly binds to O2
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O2
Hemoglobin carries O2 in the blood
Hemoglobin:
4 subunits: 2 , 2 
2o structure: all helical protein
Contains heme
coenzyme with Fe
cofactor at center
Fe cofactor directly
binds to O2
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Hemoglobin binding to O2 is reversible!!
Iron atom
O2 loaded
in lungs
O2 unloaded
in tissues
Heme group
Polypeptide chain
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O2
O2
Hb binding to O2 is affected by pH and CO2
Bohr Effect:
Decreased pH
Increases O2
unloading!!
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CO2 is transported as bicarbonate ion in blood!!
 CO2 forms carbonic acid in water
 Carbonic acid dissociates by a reversible reaction
 Ratio of acid/base regulated by mass action and
breathing rates.
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Brain
Cerebrospinal
fluid
2
1
Nerve signals
trigger contraction
of the rib muscles
and diaphragm.
Medulla
Breathing control
center responds
to the pH of blood
and cerebrospinal fluid.
Breathing is automatically
controlled
 Breathing control centers in the
brain sense and respond to CO2
levels in the blood.
 A drop in blood pH increases the
rate and depth of breathing.
Diaphragm
Rib muscles
Additional sensors in aorta may monitor O2 levels
Brain
Cerebrospinal
fluid
2
1
Nerve signals
trigger contraction
of the rib muscles
and diaphragm.
Medulla
Breathing control
center responds
to the pH of blood
and cerebrospinal fluid.
3
Nerve signals
indicate CO2
and O2 levels.
CO2 and O2
sensors in the aorta
Heart
Diaphragm
Rib muscles