Download Respiration

Gas Exchange
• Animals need a supply of O2 and a means of expelling
CO2
• They are the reactants and products of cellular
respiration
Burning man
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Respiratory medium
• Atmosphere has O2 at a partial pressure of
~159 mmHg
– Varies with altitude, about 1/2 that 18,000 feet
• Water ~ 1 ml of O2 per 100 ml of H2O at 0o
Celsius
– Varies with soluability, pressure, salts, and
temperature
– 0.7 ml of O2 per 100 ml of H2O at 15o Celsius
– 0.5 ml of O2 per 100 ml of H2O at 35o Celsius
Water vs. air as a medium
• Water
• Keeps the cells moist
• Lower oxygen
concentration than air
• Concentration varies
more
• Water is heavier
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Air
Higher conc. of O2
Faster diffusion
Needs less ventilation
Water is lost by
evaporation
• So lungs have to be
interior
Diffusion
• Cells are aquatic
• O2 has to be dissolved across a
respiratory surface to get to cells
• O2 can diffuse through a few mm of cells
• If a part of your body is more than a few
mm thick then you need a way to carry the
oxygen
• Need a large respiratory surface area
• Skin breathers
• Earthworms
– Keep moist skin and exchanges gas across
its entire surface
• Amphibians
– Supplement their lungs/gills
Form and function
• Depends on terrestrial/aquatic
environment
• Simple animals have nearly every plasma
membrane in contact with the outside
environment
– Protozoans
– Sponges
– Cnidarians
– Flat worms
• Lungs/gills
– Highly folded or branched body region
– Allow a large surface area
• Gills
– External
– Problem of losing water due to osmolarity
• Lungs
– Internal
– Allow use of air as a medium
– Terrestrial life poses problem of dessication
Gills
• Invertebrates can have simple gills
– Echinodermata: have simple flaps over much of their
body
– Crustaceans: have regionalized gills
• Ventilation: have to keep water moving over the
gills, either by paddling water in or staying on
the move
– This requires energy
– Gill slits of fish are believed to be evolutionary
ancestors of Eustachian tubes
Gills in a Tuna head
Invertebrate gills
Countercurrent exchange
• Speeds transfer of O2 to blood
• Blood and water move toward each other
in gills so as blood is more loaded with O2
its running into water with even more O2
dissolved so it can take on the maximum
load
– Gills can remove 80% of the oxygen from the
water passing over it
Tracheae
• Spiracles are holes all over an insects
body.
• From the spiracles, tubes branch out
• Finest branches (0.001mm) reach every
cell
• Insects still have circulatory system to
carry other materials
Giant insects
• By flexing they compress and expand the
tracheae like a bellows
• However insects can’t be too big because
the oxygen can’t diffuse far enough
• But ancient insects were large. How?
Lungs
• Dense networks of capillaries under
epithelium forms the respiratory surface
• Snails: Internal mantle
• Spiders: book lungs
• Frogs: balloon like lungs
• Vertebrates: Highly folded epithelium
– Humans (~ 100m2 surface area)
Lungs
• Enclosed by double walled sac whose
layers are stuck together by surface
tension, allowing them to slide past each
other
• System of branching ducts
• Nasal cavity  pharnyx  open glotis 
larynx (voicebox)  trachea (windpipe) 
2 bronchi (bronchus)  many bronchioles
 cluster of air sacs called alveoli
(alveolus)
Ventilating the Lungs
• Frogs use Positive pressure breathing:
gulp air and push it down
• Mammals: negative pressure breathing
– Suction pulls air down into a vacuum
– During exercise rib muscles pull up ribs
increasing lung volume, and lowering
pressure
– But ribs are only ~ 1/3 of Shallow breathing
Diaphragm
• Sheet of muscle at bottom of thoracic
cavity
• During inhalation: it descends
• During exhalation: it contracts
volumes
• Tidal volume: The volume of air
inhaled/exhaled
– ~500 ml in humans
• Tidal capacity: maximum volume
– ~3400 ml for girls 4800ml for boys
• Residual volume: air left in alveoli after
exhalation
Control
• Medulla oblongata/ pons
– Negative feedback loop: when stretched too
much lungs send message back to brain to
exhale
– CO2 levels are monitored in brain
• CO2 dissolves in water and forms carbonic acid
with sodium carbonate salts
• More carbonic acid lowers pH and the medulla
responds by increasing depth and rate of breathing
Hyperventilating
• Trick the brain by
purging blood of CO2
so breathing slows
Loading/Unloading gases
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Substances diffuse down the Conc. Grad.
In the atmo. There’s 760 mmHg of gas
O2 is 21% of this so 0.21 x 760 = 159
This is the partial pressure of oxygen PO2
CO2 partial pressure(PCO2): 0.23
Liquids in contact with air have the same
partial pressure
• Blood at lung: high PCO2 and low PO2
• At lungs CO2 diffuses out and O2 diffuses
in
• Now blood has a low PCO2 and high PO2
• In cells doing respiration there is a high
PCO2 and low PO2 so the CO2 diffuses into
blood and O2 diffuses into the cells
Respiratory pigments
• Colored by metals
• Invertebrates have hemocyanin which
uses copper making blood blue
• Vertebrates: hemoglobin uses iron to carry
the oxygen. Each hemoglobin can carry 4
O2s, each blood cell has many
hemoglobins
If blood is red why do your veins
look blue?
• Blood = red in its oxy’d form (i.e., leaving the lungs),
– hemoglobin is bound to oxygen to form oxyhemoglobin.
• dark red in deox’d form (i.e., returning to the lungs),
– hemoglobin is bound to carbon dioxide to form
carboxyhemoglobin.
• Veins appear blue because light,
penetrating the skin, is absorbed and
reflected back to the eye.
• Only higher energy wavelengths are seen. And higher
energy wavelengths are what we call "blue."
• From straightdope.com
Dissociation curves
• Changes in PO2 will cause hemoglobin to
pick up or dump oxygen
• Lower PO2 means hemoglobin will dump
oxygen
• Bohr shift: Drops in pH makes hemoglobin
dump O2
Diving mammals
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Weddell seals
Dive 200 – 500 m
20 min – 1 hr. under water
Compared to us it has ~ 2xs as much O2
per kg of wieght
• 36% of our O2 is in lungs 51% in blood
• Seals have 5% and 70% respectively
– more blood, huge spleen stores 24L blood
– More myoglobin (dark meat)
– Slow pulse
Liquid Breathing
• Perfluorocarbon liquids
• ~65 mL O2 per 100 mL
• Problems with expelling the
CO2
• Remember this is a liquid 1.8
times as dense as water so it
is hard to breath
• Could someday be used for
diving, or medical
applications