Mechanics of Breathing and
Gas Exchange-Transport

LECTURE OUTLINE (CHAPTERS 17 and 18)

LECTURE OBJECTIVES

1. Explain how the functional anatomy of the respiratory system relates to gas exchange.
2. Cover the physical laws associated with respiratory mechanics of the lung.
3. Describe the factors that prevent lung collapse.
4. Establish that the mechanisms for breathing at rest and forced breathing during exercise are different.
5. List measures of lung capacity and how they are used in diagnosis.
6. Describe the physical laws governing gas exchange in the lung.
7. Explain that breathing is largely involuntary and originates in multiple neural centers in the brain stem.
8. Describe how oxygen and carbon dioxide are transported in the blood.
9. Explain the significance of the oxygen dissociation curve and the factors that influence it.
10. Cover which factors in the blood and ECF influence rate and depth of breathing.

LECTURE OUTLINE

I. INTRODUCTION TO THE RESPIRATORY SYSTEM 

  A. Internal verses external respiration
  B. Functions of the respiratory system
     
II. ORGANIZATION AND FUNCTION OF THE RESPIRATORY SYSTEM

  A. Functional anatomy:  A brief review
     1. Lung and pleural cavity
          a. Muscles association with ventilation
     2. Ventilation (Animation)
          a. Quiet breathing 
          b. Forced breathing
     3. Gas Exchange occurs in the alveoli of the lung 
     4. A spirometer measures capacity for air exchange in lung 
     5. Lung disease
          a. Emphysema and smoking (Image of smoker's lung)
          b. Tuberulosis (Image of tuberular lung)
          c. Cystic fibrosis (CF) 

III. PHYSICAL BASIS FOR GAS EXCHANGE

  A. Physical characteristics of gases
     1. Air is a mixture of gases
     2. Partial pressure of a gas
          a. A gas diffuses down its partial pressure gradient
     3. Boyle's Law and lung function. 
          a. Relationship between intrapleural and alveolar pressures
          b. Transmural pressure gradient determines inspiration/expiration.
  B. Gas solubility for oxygen and carbon dioxide 

IV. GENERAL FUNCTIONS FOR RESPIRATORY PIGMENTS

  A. Gas exchange in lungs and tissues--review 
  B. Biophysical basis for gas transport in the blood
     1. General functions for Hemoglobin (Hb)
     2. Role of the heme 
     3. Role of protein (globin)
         a. Hb and myoglobin
         b. Sickle-cell anemia (if time permits) 

V. PHYSIOLOGICAL CHARACTERISTICS OF BLOOD  

  A. Oxygen capacity
  B. Oxygen affinity
     1. Oxygen dissociation curves
          a. Oxygen levels in the blood returning to and leaving the heart
          b. Comparison of Hb and myoglobin oxygen dissociation curves
     2. Environmental effects shifting the dissociation curve
         a. Decreased pH (Bohr Effect)
         b. Increased temperature and CO2
         c. 2,3 Diphosphoglycerate (2,3 DPG)
         d. Increased solute concentration 
     3. Fetal Hb

VI. CARBON DIOXIDE TRANSPORT IN BLOOD

  A. There are a number of possibilities for transport of carbon dioxide
     1. Dissolved gaseous carbon dioxide & carbonic acid in plasma 
     2. Carbonic acid inside the RBC
          a. Carbonic anhydrase
          b. "Choride shift"
     3. Carbamino compounds      
  B. Buffering effect of Hb
  C. Regulation of blood pH 
     1. Role of the carbon dioxide reservoir in lung 

VII. NEURAL AND HUMORAL CONTROL OF BREATHING

  A. Respiratory center in medulla
     1. Breathing at rest
          a. Neural activity at rest
          b. Functional organization of the "respiratory center"
               1) Dorsal Respiratory Group (DRG)
               2) Pre-Boetzinger complex
          c. Other neural inputs influencing the respiratory center
              1) Pneumotaxic center
              2) Apneustic center
              3) Hering-Breuer reflex
     2. Chemical (=Humoral) effects on ventilation rate 
          a. Peripheral effects act via the blood
               1) Low oxygen is sensed by the carotid body and aortic arch
               2) Carbon dioxide
               3) pH (e.g. lactic acid)
          b. Central effects act in the brain
               1) Importance of pH 
     3. Forced breathing
          a. Ventral Respiratory Group (VRG)
   B. Summary on control of breathing
Reading Assignment. For Thursday, March 20th, please read Chapter 19 and the first part of Chapter 20 (pages 644-652--starting with "The kidneys conserve water."). For the Tuesday following Spring Break read the rest of Chapter 20.

STUDY QUESTIONS ON RESPIRATORY SYSTEM (CHAPTERS 17 & 18)


    BASIC FACTS AND TERMS

  1. Compare and contrast hemoglobin and myoglobin. How is hemoglobin's protein structure related to its function? Besides oxygen transport, what are some other functions of hemoglobin?

  2. Distinguish between total lung volume, vital capacity, and tidal volume. What is inspiratory reserve volume and expiratory reserve volume?

  3. Distinguish between oxygen affinity and oxygen capacity of Hb. In what units is each measured? What is a normal value for oxygen capacity of blood? Oxygen affinity of Hb?

  4. Identify the brain areas that regulate breathing. How does each of these areas affect breathing? Which areas are involved in normal breathing and which in forced breathing?

  5. How do the Dorsal Respiratory Group (DRG) and Ventral Respiratory Group (VRG) in the medulla differ in function?

  6. Read about the various types of hypoxias. See Table 18-2 in Silverthron.


    CONCEPTS

  7. What is an oxygen dissociation curve? How does increased temperature, increased carbon dioxide, increased 2,3 Bisphosphoglycerate or a more acidic pH affect hemoglobin's oxygen dissociation curve? What is the physiological significance (how or why are they important) of these effects?

  8. Describe the basic steps of inspiration and expiration. Distinguish between breathing "at rest" and "forced breathing" during exercise. Which ventilatory muscles are involved in each process? See the animation on your textbook CD for a clear explanation.

  9. Why is measuring vital capacity by using a spirometer a useful diagnostic tool? What can it tell you about respiratory disease?

  10. Define the partial presssure of a gas. Calculate the partial pressure of oxygen (pO2) at sea level. The pO2 in the lungs is about 100 mm Hg at sea level. Why is the pO2 lower in the lungs than in ambient air? Explain. How would ambient pO2 change in Boulder relative to sea level? Explain this difference. Does the % of oxygen in the atmosphere different in Boulder relative to sea level?

  11. Explain how carbon dioxide is picked up in the tissues and transported in the blood? What happens to carbon dioxide when the blood arrives at the lung?

  12. People with chronic bronchitis have excessive mucous production in their respiratory pathways, and these pathways also become inflammed. Edema results. These conditions reduce the diameter of the pathways making breathing difficult. How does narrowing of the the respiratory pathways affect air flow? Explain the physical basis for your answer.

  13. Draw an oxygen dissociation curve for hemoglobin (Hb). For myoglobin. Label your axes. Which of the two has the greater oxygen affinity? Explain. What is the biophysical basis for the Hb oxygen dissociation curve being S-shaped? Why isn't the myoglobin curve S-shaped?

  14. What is the functional importance of pulmonary surfactant? How does it work? What is the law of LaPlace? What factors affect airway resistance (Review Table 17-3)?

  15. How is the lung involved in regulating blood pH? What happens to blood pH if you breathe in and out deeply several times? Explain.

  16. What is a collapsed lung? What normally keeps the lung from collapsing? See Text.

  17. A respiratory pigment that has a low oxygen affinity has difficulty picking up oxygen, but it easily unloads oxygen. Explain.

  18. What is the Bohr effect? How is the Bohr effect important for delivery of oxygen at the tissues?

  19. Breathing is modulated by a number of peripheral and central inputs. What are these? Rank them according to their importance? See Text.

  20. Flow of a gas occurs down its partial pressure gradient. What factors influence the rate of gas transfer down the partial pressure gradient?

  21. What is Boyle's Law and how is it important for understanding lung function?

  22. How does low blood oxygen trigger the carotid body into action?

  23. There are a number of respiratory diseases that affect ventilation and gas exchange in the lung. How do emphysema, fibrotic lung disease, pulmonary edema, cystic fibrosis, and asthma alter lung function? See Figure 18-4.


    REASONING AND PROBLEM SOLVING

  24. At the summit of Long's Peak, the atmospheric pressure is 440 mm Hg. Is the blood leaving the lungs saturated with oxygen at the summit? Calculate the % saturation. (Note: Remember that it is the partial pressure of oxygen within the lung, not in the ambient air, that is most important in determining blood saturation.)

  25. What is emphysema? What are its causes? A person suffering from severe emphysema often breathes from an oxygen tank to alleviate the effects of the illness. What is the physical and biological basis for this treatment? People suffering from severe emphysema also often have a high blood hematocrit. What physiological consequences of emphysema would explain their higher hematocrit? Briefly explain.

  26. Read about respiratory adaptations to high altitude in the running problem in Chapter 18. Think about what respiratory changes would occur during deep sea scuba diving?

  27. Fetal hemoglobin is different from the mother's hemoglobin in that it is fully saturated with oxygen even when the mother's is not. What blood parameter must differ for fetal hemoglobin? Defend your answer.

  28. Exercise increases forced breathing; yet, it is less clear how exercise has its effect. List at least four possibilities. Briefly explain your rationale for each.

  29. So why does this happen? If you take a fish out of water, the fish suffocates (=lack of sufficient oxygen). Likewise, if you fill the alveoli of the mammalian lung with water, the animal suffocates. What is the physical basis for suffocation in each instance?

  30. You collect the following data on your roommate: 
    			Total pulmonary ventilation (=minute volume) = 5004 ml/min
			Vital capacity = 4800 ml
			Expiratory reserve volume = 1000 ml
			Respiratory rate = 12 breathes/min
    What is your roommate's tidal volume and inspiratory reserve volume?

  31. Calculate the total pulmonary ventilation and the alveolar ventilation from the following data: 
    			Breathes/minute = 13
			Tidal volume = 450 ml
			Dead space = 150 ml



Last revised: March 13, 2008