L20 Respiratory system I

L20 Respiratory system I - The Respiratory System...

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The Respiratory System Requirements: • Relies on diffusion across a membrane, so must be thin with large surface area • Diffusion constant varies according to medium/temperature Need bulk flow of water or air, slow enough to juxtapose medium and blood, fast enough to maintain diffusion gradient • Ventilation rates or respiratory area variable – according to level of activity of organism
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WATER PROBLEMS 1. O2 content in air = 210ml/L O2 content in fresh water = 6.6ml/L (at sea level) O2 content of sea water = 5.3ml/L 2. Water much denser and more viscous than air So requires large respiratory surface and move large volumes of water, but not at too high an energetic cost. Other problems: • CO2 very soluble in water but pH may decrease • Proximity of blood and water means heat lost so same temp as environment
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Tunicates, cepahlochordates Small and inactive so NO Gills. Body & pharynx wall serve as respiratory membranes Pharyngeal slits
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GILLS External gills – many fish larvae and amphibian larvae
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L20 Respiratory system I - The Respiratory System...

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