Circulation and gas exchange II (Chapter 42)

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Circulation and gas exchange II (Chapter 42)
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Keywords

• Fish gill
• Filaments
• Lamellae
• Tracheal system
• Tracheoles
• Gastrovascular cavity
• Lung
• Tidal ventilation
• Ventilation in birds

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Fish Gill
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Rather than being a solid structure, the fish
gill is finely subdivided to enhance gas exchange
area
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filaments
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Lamellae
lamellae
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Countercurrent flow
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NOT countercurrent
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Countercurrent
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Are gills effective in increasing surface area?
Surface area
1 kg
0.06 m2
Lime jello cube
1 kg
1.16 m2

• 20 fold increase due to gills

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How do gill surface areas compare among different
fishes?

• Numbers correspond to arbitrary units per gram
  body weight

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Tracheal systems in insects
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Tracheoles supply tissues
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Diffusion distance from tracheole to mitochondria
is short
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Lungs

• Internal sacs
• Unlike insect tracheal system lungs do not
  contact entire body
• Circulatory system draws oxygen from lungs to
  tissues
• Found in snails, a few fishes, spiders,
  vertebrates

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Structure of the mammalian lung
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Tidal ventilation of mammalian lung

• Negative pressure breathing

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Tidal ventilation

• Tidal volume - volume inhaled and exhaled (around
  500 ml in humans)
• Tidal volume is much less than total volume of
  lungs (several liters in humans)
• Thus residual volume remains after exhaling
• This is inefficient

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Birds have a more sophisticated type of lung
ventilation

• Birds have high metabolic rates
• Can be exposed to lower oxygen concentrations in
  high altitude flight
• Ventilation is not tidal
• Air flows through the lungs

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The avian respiratory system
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The control of breathing

• Human brain monitors carbon dioxide level
  (detected as a drop in blood pH)
• Hyperventilation in divers
• Diving mammals can tolerate high blood carbon
  dioxide

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Organismal respiration -- a simple view
O2
O2
mitochondria
CO2
CO2
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O2
CO2H2O
HCO3-H
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Why does the body sense carbon dioxide rather
than oxygen?

• Decreased oxygen corresponds to increased carbon
  dioxide
• Increased carbon dioxide results in acidification
  which can readily be detected