Gas Exchange

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Gas Exchange
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• 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

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Water vs. air as a medium

• Water
• Keeps the cells moist
• Lower oxygen concentration than air
• Concentration varies more
• Water is heavier

• Air
• Higher conc. of O2
• Faster diffusion
• Needs less ventilation
• Water is lost by evaporation
• So lungs have to be interior

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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

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• Skin breathers
• Earthworms
• Keep moist skin and exchanges gas across its
  entire surface
• Amphibians
• Supplement their lungs/gills

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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

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• 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

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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

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Gills in a Tuna head
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Invertebrate gills
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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

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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

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Giant insects

• By flexing they compress and expand the tracheae
  like a bellows
• However insects cant be too big because the
  oxygen cant diffuse far enough
• But ancient insects were large. How?

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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)

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• 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)

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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

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Diaphragm

• Sheet of muscle at bottom of thoracic cavity
• During inhalation it descends
• During exhalation it contracts

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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

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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

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Hyperventilating

• Trick the brain by purging blood of CO2 so
  breathing slows

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Loading/Unloading gases

• Substances diffuse down the Conc. Grad.
• In the atmo. Theres 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

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• 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

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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

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If blood is red why do your veins look blue?

• Blood red in its oxyd form (i.e., leaving the
  lungs),
• hemoglobin is bound to oxygen to form
  oxyhemoglobin.
• dark red in deoxd 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

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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

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Diving mammals

• 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

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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

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