Gas Exchange

Axolotl; notice the external gills    All animals have evolved some type of system or structures to handle the exchange of gases. The solutions are many and depend on the species and its evolutionary history. The process may vary over the life cycle and may depend on environmental conditions. Sometimes it is a relatively simple solution (e.g. in a jelly fish) while in other animals (such as in vertebrates) complex systems have evolved to handle the task. The ultimate cause of all of these structures are linked to Cellular Respiration. This process needs oxygen to proceed (recall - oxygen is the final electron acceptor in the electron transport chain). In addition, the same process produces an excess of carbon dioxide in the tissues. The excess leads to a lowered pH which can have grave consequences. In this chapter you will explore the diversity of solutions to the problem of exchanging gases at the same time as you gain a deeper understanding of the process in humans.

The following questions will help you to review the material from the lecture, as well as the text. Make sure to take a look at the links to the images and the web sites at the end of the page. I have also included suggested reading material in case you would like to follow up on any of the aspects covered in this section.
Review Questions:
  1. Why is gas exchange a necessity (from a cellular perspective)?
  2. Briefly explain the process of cellular respiration (include the following processes: glycolysis, the Krebs cycle and the electron transport chain (ETC) in your answer)!
  3. Where does the carbon dioxide originate from? Why does it need to be removed from the organism? What will occur if the carbon dioxide accumulates within the organism?
  4. What is the importance of accessing oxygen? What exactly is it used for? What happens if there is no oxygen available?
  5. The term 'respiratory system' is typically used to refer to the system involved in providing gas exchange for the organism. What is the main physical process that is used for the actual movement of the two gases? Can the respiratory system handle this process alone in a larger organism?
  6. Why does the surface area of the exchange surface be large as well as moist?
  7. How does the amount of available oxygen vary between aquatic and terrestrial environments?
  8. What are the major types of gas exchange systems that have evolved in animals?
  9. Describe the use of external surfaces (skin/epithelium) in gas exchange. Describe the actual process of gas exchange. Give several examples of animals that use this method. What is the crucial factor in terms of being able to use this type of gas exchange?
  10. Are animals that use external surfaces for gas exchange restricted to that method? Give examples animals that combine several types of gas exchange.
  11. Explain the concept of gills in animals. Is there a connection between gills and the circulatory systems in animals?
  12. Give examples of several different types of animals with gills?
  13. Make a drawing of the tracheal system in an insect. Label important structures.
  14. Describe the process of gas exchange in the tracheal system in the insects. How does the animal control the level of gas exchange?
  15. Describe the structure of a book lung as found in a spider (use a drawing).
  16. What are the basic characteristics of a lung?
  17. Where does gas exchange occur in a mammalian lung?
  18. How does a bird lung differ from a mammalian lung? Briefly explain the process of gas exchange as it occurs in a bird lung.
  19. Make a drawing of a human lung and label important parts in the upper as well as the lower respiratory tract. What are the functions of the different parts?
  20. How is it possible that inhaled air will be clean, humid and warm as it reaches the alveoli of the lungs?
  21. What is the importance of the alveoli?
  22. Explain the process of gas exchange as it occurs between the alveoli and the capillaries in a human lung.
  23. Why are the epithelia of the capillaries and the alveoli so thin?
  24. Describe the structure of lung tissue as viewed in a light microscope.
  25. Explain the process of negative pressure breathing.
  26. What factors control breathing in a human? Where is the breathing control center located?
  27. How is oxygen transported with in the blood? Describe the variety of proteins used in animals for this purpose!
  28. What is a heme group? What is its function?
  29. There are different forms of hemoglobin (e.g. fetal versus adult hemoglobin). Explain!
  30. How is carbon dioxide transported in the circulatory system? In which chemical form is carbon dioxide transported?


Lecture Outline
Role for
 Intake of gases
 Transport of gases
 Tissue cells

Respiratory Surfaces

 Moist surface
 Link to circulation
 combined with other system
 Role of surface area

 Oxygen in water
 gill structure
 capillaries in lamella
 how would gills do on land?
 role of countercurrent flow

Tracheal System
 Air sacs
 Close connection to cells
 Compare with gills and lungs

Terrestrial vertebrates
 Breathing mechanism
Bronchi/ Bronchioles
Alveoli/ Connection to capillaries

Smoking and Lung Disease

Breathing Mechanism
Negative Pressure breathing
Role of diaphragm
Control of Breathing
 Control centers
 Link to CO2
 Increased CO2  leads to lowered pH

Gas Exchange in the body
Role of red blood cells
Fetal vs adult hemoglobin

Transport of oxygen
 (bound to hemoglobin)
Transport of carbon dioxide
 (as bicarbonate HCO3- in plasma)

Exchange of gases between the human fetus and the placenta

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Page created by: Peter Svensson
Updated: November 9,  2009