Chapter 22 Introduction to Oxygen and Carbon Dioxide Physiology

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  1. External Respiration
    1. Gas exchange
      1. with the external environment: diffusion, ventilation, etc.
      2. with the Internal environment: diffusion and circulatory system.
  2. Cellular respiration
    1. Glycolysis
    2. Kreb's Cycle, Electron transport
      1. Oxidative metabolism in mitochondria

The Atmosphere 


  1. Composition of dry air is the same to a height of at least 100 km
  2. Gas Pressure
    1. Air is a mixture of gases
      1. nitrogen (78%), oxygen (21%), argon (0.9%), and carbon dioxide (0.03%)
    2. Dalton's Law
      1. The total pressure of a mixture of gases equals the sum of the partial pressures of the individual gases in the mixture.
  3. Each gas in atmosphere contributes a partial pressure to the total atmospheric pressure.  (Figure 22.1)
    1. PN = 78.08% X 760mm = 600.6mm Hg 
    2. PO = 20.95% X 760mm = 159.2mm Hg 
    3. PCO2 = 0.03% X 760 mm = 0.2 mm Hg 
    4. Sum of partial pressures = 1 atmosphere
    5. Water vapor is variable (0-4%)
  4. Water vapor in the air
    1. varies with temperature 
    2. Relative humidity =  % of saturation for that temperature
    3. Total H2O  in mg / liter of air 
    4. 0 ˚C:  vapor pressure = 4.6 mm Hg 
    5. 100 ˚C:  vapor pressure = 760 mm Hg 
    6. Mammal lung at 37 ˚C  = 47 mm Hg
    1. Altitude and Atmospheric Pressure
      1. At sea level, 1 Atmosphere = 760 mm pressure 
      2. Decrease in Atmospheric Pressure with altitude
      3. Graph from Wikipedia: Altitude_atmospheric_pressure_variation
    Atmospheric Pressure vs. Altitude
  5. Solubilities of Gases
    1. O2 enters and CO2 leaves respiratory organs by diffusion.
    2. Gas molecules are soluble in water  
    3. Solubility coefficient [α, alpha]
    4. CO2 is 30 times more soluble than O2.
  6. Effects of Pressure and Temperature 
    1. Henry's Law
      1. Gases dissolve in liquids in proportion to their partial pressures
      2. calculates the amount of gas that will dissolve in water (or plasma) at a certain pressure
        1. Depends on gas solubility and the temperature.
    2. Effects of Temperature and Salinity on Solubility 
      1. Everyday illustrations of the effects of temperature and salinity on gas solubility (Figure 22.2)
      2.  Other solutes will also affect the amount of dissolved gas (Table 22.1)
  7. Diffusion of Gases
    1. Gases diffuse from regions of higher partial pressure to regions of lower partial pressure
  8. Many air-breathing aquatic insects have a "diffusion lung" (Figure 22.3)
  9. Figure 22.4 The principles of gas diffusion are vital knowledge for scuba divers
    1. At depth, P is very high, so more gas is dissolved in the blood.
    2. discussed in chapter 26
  10. Rate of diffusion
    1. Diffusion in air 10,000 x faster than in water at the same partial pressure (tension)
    2. Permits different dimensions in respiratory organs
  11. Replacement of air with water in the interstitial spaces of beach sand can cause anoxia in a sea turtle nest because diffusion is far slower through water than through air (Figure 22.5)
  12. Box 22.1: Respiration by diffusion alone is possible only if distances covered are < 1 mm.
    1. A 3-week-old larva of the anchovy Engraulis mordax, common along the West Coast of the United States
    2. The gills and circulatory system are undeveloped
    3. The average body diameter is 0.6 mm
    4. The oxygen demand is met primarily by diffusion
    5. Respiration by diffusion alone is possible only if distances covered are < 1 mm.
    6. Larger distances require special structures (e.g. gills, circulatory systems, etc. = allometry)
  13. Why we need circulation
    1. Radius increases proportionally to body size.
    2. any animal with a radius > 1 mm needs a circulatory system and blood.
  14. Box 22.2: Mechanisms by which ambient currents can induce flow through tubular structures
    1. Bernoulli's Principle
  15. Figure 22.6: Two Types of Convective transport
    1. Directional movement (bulk flow) rather than random diffusion of molecules.
    2. Gas transport is enhanced by convective movement
      1. Unidirectional flow
      2. Tidal flow
  16. Figure 22.7 Mechanisms of oxygen transport in the delivery of O2 to the mitochondria
    1. Gas exchange in animals usually a combination of diffusion and convection
  17. Figure 22.8
    1. Physiological oxygen cascade is analogous with a cascade along a mountain stream
    2. Organisms use differences in partial pressures to move O2 from the lungs to cells to mitochondria.
  18. Comparison of air and water as respiratory medium
  19. Work of respiration


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