General Biology 2Class 17

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General Biology 2 Class 17
Respiration in Tetrapods
OConnor and Claessens, Nature, 2005
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A Few Useful Terms and Concepts that were Covered
in Lecture
Ventilation Inspiration Expiration Convection
(and vs. diffusion and Fick's law) Elastic
recoil Natural shape (elastically unloaded
shape) Passive and active expiration
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A Bit About Diffusion and Convection
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Major Stages in the Evolution of Lung Ventilation
Mechanisms
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Elasticity and Breathing Systems

• Elastic materials, when distorted from their
  "natural shapes" can store energy.
• Many body tissues show significant elasticity.
• Lungs are good examples (and we will see others).
  Think of them like they were balloons.
• At their resting (natural shape) they store no
  energy.
• If their volumes are either increased or
  decreased they store energy that can be used to
  move them back to their original shape and to
  move air.

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• Passive Expiration
• Present in all air breathers to some degree
• In lunged fish
• Air is "inhaled" by enlarging the buccal cavity
  when the entrances to the system (mouth/nares)
  are opened.
• Closing the inputs while also reducing the
  volume of the buccal cavity produces a positive
  pressure that forces air into the lung
• fluids move down energy/pressure gradient
• note pressure is energy/volume force/area
• The increased volume expands the lungs and
  elastically loads the lung and surrounding
  tissues.
• When the buccal cavity is relaxed and airway
  entrances are opened, the lungs and surrounding
  tissue elastically rebound. This lowers volume
  and increases pressure and forces air out until
  the original shape/volume is reached.

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Schematic Representation of the Frog Respiratory
System
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Lung Ventilation in Amphibians

• Note the possibility for active expiration in
  addition to passive expiration
• Smooth muscle in the lung walls
• Abdominals contract against viscera, forcing it
  against lungs and forcing them to empty

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3. Active components for inspiration and
expiration) inspiratory expiratory
muscles. 4. Passive (elastic) components for
expiration
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The Lung - Air Sac System of Birds
From OConnor and Claessens, Nature 2005
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Principal Airways in the Goose Lung
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Airflow in the Avian Pulmonary System
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• Notes On Avian System
• Essentially unidirectional flow of air.
• Essentially continuous flow of air through the
  lungs and parabronchi.
• The fact that the air sacs are part of the
  conduction system and do not serve to increase
  the exchange surface area (CO experiments).
• Two inspiration/expiration cycles are required
  for most of the air to enter and leave the body.
• Helps adapt birds to high metabolic rate and
  operation at high altitude.

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The Skeletal Respiratory Pump and Archosaurian
Pulmonary Evolution
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Simplified Archosaur Phylogeny
Crocodylia
Theropoda
Aves
Dinosauria
Archosauria
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Pneumatic Vertebrae in Theropods Indicators of
pulmonary morphology
a, b Living Bird sarus crane
Grus antigone c, dTheropod Dinosaur
Majungatholus atopus
From OConnor and Claessens (2005) Nature
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Anatomy of the Mammalian Lung
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Differences in Compartmentalization in the
Tetrapod Lung
Purposes of these subdivisions in terms of Fick's
law? Alligator and same size human
metabolismboth at same body temperature human
energy demand is 10X higher At normal body
temperature 40X higher