Gas Exchange

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Gas Exchange
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Gas Exchange

• Animals need a supply of O2 and a means of
  expelling CO2
• They are the reactants and products of cellular
  respiration

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Respiratory medium

• Atmosphere has O2 at a partial pressure of 159
  mmHg
• Varies with altitude, its about half as much at
  18,000 feet above sea level
• Water has 1 ml of O2 per 100 ml of H2O at 0o
  Celsius
• Varies with solubility, 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 skin moist and exchange gases across their
  entire surface
• Amphibians
• Supplement their lungs with gills

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Form and function

• Depends on whether
• environment is terrestrial or aquatic
• Simple animals have nearly every plasma membrane
  in contact with the outside environment
• Protozoans
• Sponges
• Cnidarians hydra, anemones
• Flat worms

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• Lungs/gills
• Highly folded or branched body region
• Creates a large surface area for absorption
• Gills
• External
• Problem - losing water due to
• osmolarity of salt water
• Lungs
• Internal prevents drying out of
• membranes
• 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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Invertebrate gills
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Gills
Specialized for gas exchange in water. Have to
be efficient 10,000X less O2 in water than in
air. O2 and CO2 readily diffuse between blood
and water. Countercurrent Exchange blood in
capillaries flows in opposite direction from
the water passing over the gills.
Along the capillary, a steep diffusion gradient
favors transfer of oxygen into the blood.
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Countercurrent Flow in Sharks
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Countercurrent vs. Concurrent Flow
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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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Respiratory Exchange in Insects
Spiracles of Two Insects
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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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Pulmonary Circulation
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Alveolar Exchange
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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 and pons
• negative feedback loop when stretched too much
  lungs send message back to brain to exhale
• CO2 levels are monitored in the brain
• CO2 dissolves in water and forms carbonic acid
  with sodium carbonate salts
• More carbonic acid lowers pH of blood 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 atm. theres 760 mmHg of gas
• O2 is 21 of this so 0.21 x 760 159 mmHg
• This is the partial pressure of oxygen PO2
• CO2 partial pressure(PCO2) 0.23 mmHg
• Liquids in contact with air have the same partial
  pressure

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Gas Exchange at Alveoli

• 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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Gas Exchange Throughout the Body
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Respiratory pigments

• Colored by metals
• Invertebrates have hemocyanin which uses copper
  making blood blue
• Vertebrates hemoglobin which 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 is a bright red in its oxygenated form
  (i.e., leaving the lungs), when hemoglobin is
  bound to oxygen to form oxyhemoglobin. It's a
  dark red in its deoxygenated form (i.e.,
  returning to the lungs), when 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.
  Since only the higher energy wavelengths can do
  this (lower energy wavelengths just don't have
  the oomph), 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 2x
• as much O2 per kg of weight
• 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 Ventilation

• 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 (ex supporting injured lungs,
  radiology)