Ch. 42 Gas Exchange

# Ch. 42 Gas Exchange - Animal Gas Exchange Chapter 42 BIOL...

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Gas Exchange 1 BIOL 112 Animal Gas Exchange Chapter 42 BIOL 112 Gas Exchange ± All aerobic cells need O 2 and release CO 2 ± Exchange O 2 and CO 2 with environment ± All living aerobic organisms face same problem of adequate gas exchange with environment to support metabolism ± Source of gasses: atmosphere BIOL 112 BIOL 112 Air Content Sample of air at sea level, low humidity: ± 78% N 2 — biologically inert ± 20.9% O 2 — respiration gas ± 0.03% CO 2 — respiration gas ± ~1% others — mostly inert BIOL 112 Partial Pressure ± Instead of expressing component gas content in %, express in partial barometric pressure ± Barometer, invented by Evangelista Torricelli, 1643 – What holds Hg up in barometer tube? – Why does Hg go up only 760 mm against vacuum? ± Barometer measures atmospheric pressure, the “weight” of air pressing down on Hg, pushing it up the tube to fill the vacuum. The 760 mm represents the total pressure of air upon the surface of Hg ± Gas pressure can be expressed as the height of Hg in a column BIOL 112 Sea level = ~1013 millibars (mb) = 1 kg/cm 2 pressure = 1 atm = 101 kPa = 14.7 lb/in 2 = 29.91 inches Hg Height of Hg column is 760 mm. So 10 mm Hg = 13.3 mb 1 kilopascal (kPa) = 10 mb; 1 mb = 100 Newtons/sq. meter (N/m 2 )

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Gas Exchange 2 BIOL 112 BIOL 112 Do you need to use mercury? ± No ± Earlier barometer by Torricelli used water. But water is less dense (s.g. Hg, 13.55) ± Height of column in water barometer is 33 ft (11 m). Tube had to be some 40 ft or more high: a barometer two or three stories tall. Conversion to Hg made a lot of sense BIOL 112 BIOL 112 Water barometer About 11 m (33 ft) high BIOL 112 Partial Pressure ± 1 atmosphere pressure = 760 mm Hg ± Can parse the contributions of each gas to the total air pressure: partial pressure –pPN 2 = 760 x 78% = 593 mm –pPO 2 = 760 x 21% = 159 mm –pPCO 2 = 760 x 0.03% = 0.2 mm ± Partial pressure is a more biologically significant expression of available gas concentration for gas exchange BIOL 112 High Altitude Physiology pPO 2 ± 10,000 ft, P = 523 mm; 21% O 2 110 mm ± 20,000 ft, P = 349 mm; 21% O 2 73 mm ± 50,000 ft, P = 87 mm; 21% O 2 18 mm
Gas Exchange 3 BIOL 112 BIOL 112 Humans at High Altitude ± Humans at 15,000 ft or higher show mental and physical impairment within an hour or less from hypoxia –pPO 2 < 90 mm Hg, trouble for humans –pPO 2 < 40 mm Hg, brain dies quickly ± Solutions to problem? Breathe pure O 2 ; pPO 2 = P total Upper limit: 40,000 ft, P = 100 mm. Above 40,000 ft, even pure oxygen can’t support life. Why? Pressurize cabin Commercial airlines pressurize to ~10,000 ft, even though aircraft routinely fly at 30,000–40,000 ft BIOL 112 Comparative Gas Exchange Cell needs to be 1 mm from environment for adequate gas exchange access ± Simple organisms: protozoa, primitive metazoa, have no special exchange structures ± Bigger organisms, and especially land organisms, need specialized exchange structures – Fish and other aquatic organisms:

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Ch. 42 Gas Exchange - Animal Gas Exchange Chapter 42 BIOL...

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