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review questions

  1. If you don't have your Introductory Biology textbook,
    1. here is the Respiratory System from the On-line Biology book.
    2. Vertebrate Lungs from Kimball's Biology Pages
    3. Tracheal systems from Kimball's Biology Pages


  1. Fig 23.1 Generalized features of animal gas exchange
  2. Why we need gas exchange systems
    1. As organisms grow larger, their ratio of surface area to volume decreases
    2. This limits the area available for diffusion and increases the diffusion distance
    3. Surface [O2 ] would be depleted if r > 1mm.
  3. Animals typically have respiratory organs
    1. The ratio of 'respiratory surface area' to 'body surface area' needs to increase as body size increases
    2. In humans, the lung surface area is 50-100 m2, and the remaining body surface area ~ 2 m2
  4. Specialized gas exchange surfaces (Fig. 23.2)
    1. Gills: evaginated. May be secondarily enclosed in a cavity
    2. Lungs: invaginated
    3. Cutaneous: amphibians
    4. Tracheae: insects
  5. Ventilation
    1. reduces static boundary layers
    2. Passive ventilation relies on water and air currents
    3. Tidal ventilation
    4. Unidirectional ventilation
  6. Fig 23.3 Tidal gas exchange: O2 transfer from the environmental medium to the blood in a tidally ventilated lung
    1. Differences in partial pressures drive respiratory fluid
  7. Figure 23.4a Cocurrent exchange: A modes of O2 transfer from the environmental medium to the blood when ventilation is unidirectional
  8. Figure 23.4b Countercurrent gas exchange: A mode of O2 transfer from the environmental medium to the blood when ventilation is unidirectional
  9. Figure 23.5 Cross-current gas exchange: A third mode of O2 transfer from the environmental medium to the blood when ventilation is unidirectional
  10. Fig 23.7 Total area and thickness of the gas-exchange membrane in the gills or lungs of vertebrates as functions of body size
    1. allometric relationship
  11. Figure 23.7 Total area and thickness of the gas-exchange membrane in the gills or lungs of vertebrates as functions of body size
    1. Fish, amphibians, and reptiles have smaller surface areas.
    2. Birds and mammals have high surface areas
  12. Figure 23.8 The percentage of O2 and CO2 exchange that occurs across the skin
    1. Aquatic and semiaquatic tetrapods have higher rates of cutaneous respiration
  13. Ventilation and Gas Exchange
    1. Air breathers use tidal ventilation
    2. water breathers use unidirectional flow.
  14. Challenges in Breathing Water
    1. Water is 1,000 times as dense as air
    2. Water has 1,000 times greater viscosity
    3. The solubility of O2 is 30 times lower in water
  15. Advantages in Breathing Water
    1. It is easier to get rid of CO2
    2. Air breathing causes dehydration
  16. Ventilation of Gills
    1. vertebrates have pharyngeal gills
  17. Figure 23.10 The branchial breathing system in teleost (advanced bony) fish
    1. Gas exchange occurs in the secondary lamellae
  18. Countercurrent Flow in Fish Gills
    1. Countercurrent blood flow relative to direction of water flow through buccal cavity
  19. Gill Ventilation in Bony Fish
  20. Figure 23.11 The breathing cycle in teleost fish
    1. Water pumping
      1. Buccal (oral) Pump
      2. Opercular pump
    2. Higher pressure in the oral versus opercular cavity
  21. Ram Ventilation
  22. Air Breathing Fish
  23. Water to Land
    1. A few members of aquatic groups (mollusks, arthropods and fish) came on land.
    2. Gills collapse
    3. Water evaporation of gills
  24. Figure 23.13 Breathing organs of amphibians
    1. Cutaneous respiration
    2. External gills
    3. Simple bilobed lungs; more complex in terrestrial frogs and toads
  25. Figure 23.14 The three major steps in the ventilatory cycle of an adult bullfrog (Lithobates catesbeianus)
    1. frog takes air into mouth
    2. closes mouth and nostrils
    3. forces air into lungs by elevating floor of mouth (positive pressure)
  26. Cutaneous Respiration
  27. Figure 23.15 The development of external respiration in the bullfrog
  28. Gills/skin as tadpoles
  29. Lungs/skin as adults
  30. Carbon dioxide excretion versus oxygen absorption
  31. Figure 23.16 Reptile lungs
    1. Most have two lungs; in snakes one lung is reduced or absent
    2. Can be simple sacs with honeycombed walls or highly divided chambers in more active species
  32. Reptile Ventilation
    1. Tidal
    2. Rely on suction pumps (negative pressure)
  33. Mammal Respiratory Tracts
    1. Upper respiratory tract: mouth, nasal cavity, pharynx, trachea
    2. Lower respiratory tract: bronchi and lungs
    3. The airways of the lungs are the bronchioles and alveoli
    4. The alveoli are the sites of gas exchange
  34. Figure 23.17 The airways in human lungs
    1. tidal ventilation
    2. highly vascularized
    3. high surface area
    4. low diffusion distances
  35. Figure 23.18 Respiratory airways of the mammalian lung
    1. frog 1 cm3 = 20 cm2 surface area
    2. mouse 1 cm3 = 800 cm2 surface area
    3. alveolar membrane 0.2 microns
    1.   The total lung capacity (TLC) of an adult male is about 6000 ml and is divided into two categories; vital capacity (VC) and residual volume (RV).  
    2. Fig. 23.19 Dynamic lung volumes in healthy young adult men
      1. Tidal volume (VT): total volume of air inspired or expired at rest during a normal inspiration or expiration and is about 500 ml.
      2. Inspiratory reserve volume (IRV): amount forcibly breathed in above tidal volume and is about 3000-3100 ml.
      3. Expiratory reserve volume (ERV):  the maximal amount of air that can be forcibly exhaled after a normal tidal exhalation and is about 1000-1200 ml.
      4. Residual volume: refers to the volume of air that remains in the lungs after a maximal exhalation, and is about 1200 ml. 
    3. Dead Space
      1. Volume of air held in parts of lung with no exchange surfaces
      2. Anatomical dead space
      3. Alveolar dead space
    4. Lung Volumes and Capacities
    5. Figure 23.20 Mechanisms of gas transport in the final branches of mammalian lungs during inhalation
      1. Bulk flow down to the bronchioles
      2. Gases in the alveoli are motionless


    Lung volumes from Wikipedia.  Illustration by Vihsadas.

      1. Path of Air:
        1. nasal cavity:
        2. pharynx with epiglottis
        3. larynx
        4. trachea
        5. bronchi
        6. Lungs
          1. bronchioles
          2. alveoli
        1. Ventilation  
          1. diaphragm
          2. inhalation (inspiration)
          3. exhalation (expiration)


    Image from Wikipedia.  This image has been released into the public domain by its author, LadyofHats.

      1. Bird lungs are smaller and less compliant than lungs of a similar sized mammal.
      2. When birds inhale, their lungs contract, and when birds exhale, their lungs expand.
      3. Bird airways, lungs, and air sacs are interconnected.
    3. Birds
      1. Lungs (parabronchi) are stiff and change little in volume
      2. Rely on a series of flexible air sacs
      3. Gas exchange occurs at parabronchi
    4. Figure 23.23 Parabronchi and air capillaries: The gas-exchange sites in avian lungs
    5. Respiration in birds
      1. Requires two cycles of inhalation and exhalation
      2. Air flow across the respiratory surfaces is unidirectional
    6. Figure 23.22 Airflow in the lungs and air sacs of birds
      1. Figure by L. Shyamal from bird respiratory system in Wikipedia


    1. Figure 23.29 Insects breathe using a tracheal system of gas-filled tubes that reaches all tissues from the body surface
    2. Insects and arachnids
      1. Combine "circulation" and gas exchange into a single structure
      2. Have an extensive tracheal system - series of air-filled tubes
      3. Tracheoles: terminating ends of tubes that are filled with hemolymph
        1. Open to outside via spiracle
        2. Gases diffuse in and out
        3. Tracheal systems from Kimball's Biology Pages





Aquatic Animals
  1. diffusion
    1. protists  
    2. cutaneous respiration: small invertebrates - e.g. sponges, cnidarians, and planarians.
  2. gills
    1. invertebrates
      1. mollusks gills  
      2. crustaceans
      3. polychaete annelids  


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