Biology 2672a: Comparative Animal Physiology

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Biology 2672a Comparative Animal Physiology

• Breathing in air

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Gas transport in organisms - a combination of
convection and diffusion
Unidirectional flow (convection) in circulatory
system
Tidal convection ventilates lungs
Diffusion from capillaries into tissues
Diffusion into bloodstream
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Concurrent gas exchange
Fig. 21.4a
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Countercurrent gas exchange
Concurrent
Fig 21.4b
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Countercurrent gas exchange
Concurrent
Fig 21.4b
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Cross-current gas exchange
Fig. 21.5
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Mammal lungs are inefficient
Fig. 21.19
Fig. 21.3
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Breathing Air

• Lots of Oxygen!
• Not so easy to get rid of CO2
• Problems with water loss
• Lungs (invaginations)

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(Most) Fishes Breathing Air
Plecostomus - Gut
Electric Eel - Mouth
Bowfin Swim bladder
Fig. 23.15
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Tracheal system
Fig. 22.29
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Construction of the tracheal system

• A branched series of tubes that are filled with
  air (except at the very ends)
• TracheagtTracheoles
• Terminal tracheoles
• Constructed from a single invaginated cell
• Distance between lumen cell 3 x cell
  membranes
• Fluid-filled

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Tracheal system

• Very extensive
• no cell is more than 2-3 cell diameters from a
  tracheole
• Tissues with high metabolism (e.g. flight muscle)
  may have at least one terminal tracheole
  penetrating each cell (!)
• On-tap oxygen in every cell!

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Gas transport in the tracheal system

• Diffusion works very well in gases
• Some convection
• Thorax abdomen pumping
• Caused by partial pressure gradients?
• Tracheal pumping? (see movie on WebCT)
• One-way flow systems
• Ram ventilation (draft ventilation)

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Mammal lungs
Trachea
Bronchus
Alveoli
Alveolar duct
Terminal Bronchiole
Respiratory bronchiole
Fig. 21.18
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Breathing air while flying

• Energetic costs of flying are 2.5-3 higher than
  running
• Two groups of extant flying vertebrates

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Insects -Tracheal system reaches every cell
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Ways to maximise O2 uptake

• Countercurrent exchange
• Reduce diffusion distance
• Increase flow rate
• Increase absorption of O2

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Bird lungs a one-way system
Fig. 22.24
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The bird lung - orientation
Anterior Air Sacs
Anterior 2 bronchus
Parabronchi
Posterior 2 bronchus
Posterior Air Sacs
1 bronchus
Mesobronchus
Beak
Butt
Fig. 22.22
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Bird lung Breathe in
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Bird lung Breathe Out
See also Fig 22.22
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Bird Lungs Gas-blood

• Highly efficient
• gt37 of O2 extracted from the air
• Mammals 25
• Thin blood-gas barriers
• Surface area body size same as mammals
• Surface area lung volume 2 mammals

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Bird Lungs Cross-current gas exchange
Fig. 22.23c
Fig. 22.5
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Ways to maximise O2 uptake

• Countercurrent exchange
• Reduce diffusion distance
• Increase flow rate
• Increase absorption of O2

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Bat lungs

• Mammalian alveolar dead space (etc)
• Equivalent O2 uptake to birds
• ?Heart size, ?Heart output
• ? Haematocrit
• Large lungs
• ?Surface area
• ?pulmonary blood volume
• ?thickness of blood-gas barrier

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Bats vs birds

• Largest birds (18 kg) much larger than largest
  bats (1.5 kg)
• Birds function perfectly well (fly!) at high
  altitude
• Geese over Mt Everest
• Vulture in jet engine at 11.2 km
• High altitude climbers not plagued with bats

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Reading for Thursday

• Blood
• Pp581-603