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GAS EXCHANGE
Key concepts
 Gas exchange occurs across specialized respiratory
surfaces
 Gills in aquatic animals
 Tracheal systems in insects
 Lungs
 Breathing ventilates the lungs
 Amphibian breathing
 Bird breathing
 Control of breathing in humans
 Respiratory pigments bind and transport gases
 Diffusion and partial pressure
 Respiratory pigments
 O2 and CO2 transport
Vocabulary words
 respiratory
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surface
tracheal system
larynx
bronchi
(bronchus)
breathing
vital capacity
partial pressure
dissociation
curve for
hemoglobin
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ventilation
lungs
vocal cords
bronchioles
diaphragm
residual
volume
respiratory
pigments
Bohr shift
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countercurrent
exchange
gills
trachea
alveoli
(alveolus)
tidal volume
breathing
control centers
hemoglobin
carbon dioxide
transport
Respiratory surfaces and gas exchange
 Gas exchange – uptake of
O2 from environment and
discharge of CO2
 Mitochondria need O2 to
produce more ATP, CO2 is
the by-product
C6H12O6 + 6O2  6CO2 + 6H2O + 36 ATP
 Diffusion rate
 α SA  large
 α 1/d2  thin
 Moist so gases are dissolved
first
DIFFUSION
Respiratory surfaces and gas exchange
 Respiratory surface
 Simple invertebrates
 Size of organism
 Sponges, cnidarians,
 Habitat
flatworms
 diffusion
 Metabolic demands
 Unicellular organisms
 Entire surface area for
diffusion
Respiratory surfaces and gas exchange
 More complex animals
 Thin, moist epithelium
 Separates medium from
capillaries
 Entire outer skin  small,
long, thin organisms
 Specialized respiratory
organs that are extensively
folded and branched
Gills in aquatic animals
 Outfoldings of the body
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surface suspended in
water
Sea stars
Segmented worms or
polychaetes
Molluscs and
crustaceans
Fishes
Young amphibians
Total surface area is
greater than the rest of
the body
Water as a respiratory medium
 Surfaces are kept moist
 O2 concentrations in water
are low
 Ventilation – increasing
flow of respiratory medium
over the surface
 Countercurrent exchange –
process in which two fluids
flow in opposite directions,
maximizing transfer rates
 Why are gills impractical
for land animals?
Just keep
swimming
swimming
swimming!
Air as a respiratory medium
 Air has a higher
concentration of O2
 O2 and CO2 diffuse
much faster in the air
 less ventilation
 Difficulty of keeping
surface moist
 Solution: respiratory
infolding inside the
body
 Tracheal system of insects –
network of tubes that bring O2
to every cell
Spiracles
Lungs
 Heavy vascularized
invaginations of the body
surface restricted to one
location
 Found in spiders, terrestrial
snails, vertebrates
 Amphibians supplement
lung breathing with skin
 Turtles supplement lung
breathing with moist
surfaces in mouth and anus
Mammalian
respiration
Lung ventilation through breathing
 Positive pressure
 Negative pressure breathing in reptiles and
breathing in frogs
 “Gulping in” air
 Rib muscles and diaphragm change lung volume
mammals
and pressure
Lung volumes
 Factors
 Sex
 Height
 Smoking
 Physical activity
 Altitude
 Tidal volume
 Volume of air inhaled and
exhaled with each breath
 Vital capacity
 Maximum volume inhaled
and exhaled during forced
breathing
 Residual volume
 Air left in alveoli after forced
exhalation
Avian breathing
Air sacs act as
bellows to keep air
flowing through the
lungs.
Control
centers in
the brain
regulate
breathing
Gases
diffuse down
pressure
gradients
concentration and
pressure drives the
movement of gases into
and out of blood
Respiratory
pigments
 O2 transport
 Low solubility of O2 in
H2O
 Respiratory pigments
are proteins with metal
atoms
 Hemoglobin – Fe
 Hemocyanin – Cu
 Allow reversible binding of
O2
 Drop in pH results in a
lowered affinity of
hemoglobin for O2
 CO2 transport
Respiratory
pigments
 7% in plasma
 23% bound to
hemoglobin
 70% as HCO3 buffer
Fetal hemoglobin
HbF has greater affinity to O2 than Hb
 low O2% by time blood reaches placenta
 fetal Hb must be able to bind O2 with greater
attraction than maternal Hb
Deep-diving
mammals
 Seals, whales, dolphins are
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capable of long underwater
dives
Weddell seal  5% O2 in
lungs, 70% in blood
Huge spleen stores huge
volumes of blood
Large concentrations of
myoglobin in muscles
Heart rate and O2
consumption rate decrease
Blood is redirected from
muscles to brain spinal
cord and eyes