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Respiration
AP Biology
Unit 6
Types of Respiratory Systems
• Animals typically do gas exchange through
one (or more) of the following means:
–
–
–
–
Skin (body surface)
Gills (internal or external)
Lungs
Tracheal System
Respiratory Media
• Both air and water can serve as respiratory
media (what is being “breathed” in)
– Ex. Fish respire water, humans respire air
• What are the advantages of respiring air
versus water?
Air as a respiratory media
• Advantages
– Lighter
– Contains more O2
• Disadvantages
– Membranes dry out more easily (moisture
needed)
Water as a media
• Advantages
– Keeps membrane moist (so they continue
functioning properly)
• Disadvantages
– Heavier
– Contains less O2
Respiratory Systems: Gills
• Fish use their gills as a respiratory surface
• Water flows in through mouth, across the
gills, then out through the operculum
• As the water flows across the gills, O2
diffuses into the capillaries in the gills, CO2
diffuses out.
Respiratory Systems: Gills
• Water flows across the gills in the opposite
direction as the blood flowing in the
capillaries = Countercurrent Flow
Image taken without permission from http://bcs.whfreeman.com/thelifewire/
Respiratory Systems: Gills
• Why is countercurrent exchange an
effective way to get O2 from water?
(especially compared to concurrent flow)
Image taken without permission from http://bcs.whfreeman.com/thelifewire/
Respiratory Systems: Gills
• Countercurrent flow
is an effective way to
get O2 because as the
blood flows, it
always meets water
that is more highly
oxygenated 
allows O2 to diffuse
into the blood along
the entire length of
the gills
Image taken without permission from http://bcs.whfreeman.com/thelifewire/
Tracheal Systems
• Insects have spiracles which
open up to the outside
• Air flows in from the
spiracles and through the
tracheae
• The tracheal system is so
extensive that this allows air
to flow right next to the body
cells
Question…
• How does the tracheal system allow insects
to maintain a high metabolic rate despite
having an open circulatory system?
– They don’t use their circulatory system to
transport O2 to cells– flows directly from
tracheae to cells  open circulatory system not
a factor
Respiratory Systems: Birds
• Birds have air sacs and lungs
• Air sacs = for storing air (no gas exchange
occurs here)
• Lungs – where gas exchange (O2 into blood
and CO2 out) occurs
Respiratory Systems: Birds
• Birds have one way flow through their
lungs
• Animation
Question…
• How does a bird’s respiratory system allow
it to maintain high levels of activity, even at
high altitudes (where there is less O2)?
– One way flow means that the most oxygenated
air is always flowing across the lung surfaces
– There is no “old/stale” air left over in the lungs
that takes up space
Mammalian Respiratory System
• Pathway of air
• Nasal cavity & mouth  pharynx (back of
throat  trachea  bronchi  bronchioles
 alveoli
Mammalian Respiratory System
• Trachea
– Windpipe
– Lined with rings of cartilage
for structural support
• Bronchi
– Main branches leading from
trachea
• Bronchioles
– Smaller branches (no
cartilage rings)
Alveoli
• Air sacs with very thin walls
• Surrounded by lung
capillaries
• Where gas exchange occurs
• Random fact: You have
approximately 300 million
alveoli in your lungs– surface
area is equivalent to ¼ of a
basketball court
Inhalation
• Inhalation = taking air into
the lungs
• Diaphragm contracts
(flattens)  space in chest
cavity expands (pressure
lowered)  air from outside
is sucked in (flows from
high to low pressure)
Exhalation
• Exhalation = air leaves the
lungs
• Diaphragm relaxes (moves
up)  less space in chest
cavity  air is pushed out
of lungs
Diffusion of Gases in the Alveoli
• Diffusion of O2 and CO2 in the lungs
(alveoli) is caused by differences in partial
pressure
• Partial pressure = pressure due to one
particular gas (kind of like concentration)
– PO2 = partial pressure due to O2
– PCO2 = partial pressure due to CO2
Diffusion of Gases
• Oxygen diffuses into
the capillaries from the
alveoli (PO2 in the
capillaries is lower
than PO2 in the alveoli)
• CO2 diffuse into the
alveoli from the
capillaries (PCO2 in the
capillaries is higher
than PCO2 in the
alveoli)
Transport of Oxygen in the Blood
• Oxygen is transported by hemoglobin in red
blood cells
– Each hemoglobin molecule can carry 4 O2
molecules
– Cooperative binding = once the first O2 binds,
the next 3 are able to bind more easily
Bohr Effect
• pH changes hemoglobin’s
affinity (ability to bind) for
oxygen  Bohr effect
• At lower pHs, hemoglobin
doesn’t bind O2 as well 
lets it go into the
surrounding tissues
Question…
• Why would it make sense to drop off more
O2 when the pH is lower?
– Lower pH is due to lactic acid from
fermentation
– This means the cells in that region need more
O2  hemoglobin drops it off more readily
Hemoglobin affinity
• Certain organisms also
have hemoglobin with a
high affinity for oxygen
– Fetus has a higher affinity
for O2 compared to its
mother
– Llamas have a higher
affinity for O2 compared to
animals who live at sea
level
Image taken without permission from http://bcs.whfreeman.com/thelifewire/
Question…
• Why would a fetus have hemoglobin with a
higher affinity for O2 than its mother?
• The only way for a fetus to get O2 is from
its mother (umbilical cord)  it has to be
able to have hemoglobin that can “grab” O2
from its mother’s bloodstream
Question…
• Why would a llama have hemoglobin with a
higher affinity for O2 compared to other
mammals?
• At higher altitudes, there is less O2 in the air
(lower PO2)  llamas have to be able to
grab more O2 at a lower PO2 to get enough
to survive.
Transport of CO2
• CO2 is mostly
transported as HCO3(bicarbonate ions) in the
blood plasma
• After CO2 diffuses into
the blood from the body
cells, carbonic anhydrase
(enzyme in RBC)
converts CO2 into
bicarbonate ions
Transport of CO2
• When the bicarbonate reaches the lungs, the
carbonic anhydrase converts it back into
CO2 gas  it diffuses out into the alveoli
Control of Respiration
• Regulated by brain
(medulla oblongata and
pons) that controls the
diaphragm and rib
muscles to change rate or
depth of breathing
• Sensors send messages to
brain from elsewhere in
body
Control of Respiration
• Messages include those
about:
– O2 concentration (only
when very low)
– pH of blood (related to
CO2 concentration)
Control of Respiration
• CO2 / blood pH has a much stronger effect
on breathing rate than O2 levels
5 slides left
Question…
• How would holding your breath affect your
blood pH?
– It would cause pH to drop since CO2 is not
being eliminated
4 slides left
Marine Mammal Diving Reflex
• When marine mammals dive,
their heart rate goes way
down– sometimes it goes
down to 3 or 4 beats a
minute
• This is the diving reflex
3 slides left
Marine Mammal Diving Reflex
• Blood is sent primarily to
the brain, eyes and adrenal
glands
• Blood flow to muscles is
shut off – it just uses the O2
stored in the myoglobin in
muscles
– Myoglobin is an oxygen
carrying molecule in muscles
2 slides left
Marine Mammal Diving Reflex
• What adaptations does the marine mammal
have to allow them to stay underwater for a
long time (sometimes up to 2 hrs)?
– Lots of myoglobin to store O2 in muscles
– More blood to store more O2
– Huge spleen
1 slide left
Human Diving Reflex
• Humans have a similar reflex
• When your face is submerged, your heart
rate goes down
• Might be a protective response during birth
when the pressure can prevent O2 from
getting to the baby from the umbilical cord
 slowing down blood flow slows down O2
depletion in blood
Last slide! 