1. chapter 6
The Respiratory System and Its Regulation

2. Learning Objectives
Find out how the respiratory system brings oxygen to muscles and tissues and rids the body of carbon dioxide
Learn the steps involved in respiration and gas exchange
Discover how your respiratory system regulates your breathing and gas exchange

3. Anatomy of the Respiratory System

4. Transportation of Oxygen and Carbon Dioxide
Pulmonary ventilation (breathing): movement of air into and out of the lungs
Pulmonary diffusion: the exchange of O2 and CO2 between the lungs and the blood
Transport of O2 and CO2 via the blood
Capillary diffusion: the exchange of O2 and CO2 between the capillary blood and the metabolically active tissue

5. Pressure1 x Volume1 = Pressure2 x Volume2
Boyle’s Law
If temperature is constant:
Pressure1 x Volume1 = Pressure2 x Volume2

6. Pulmonary Ventilation
Inspiration: active process involving the diaphragm and the external intercostal muscles
Pressure in the lung is less than the air pressure outside the body, air following the pressure gradient coming into the lung
Expiration: usually a passive process involving relaxation of the inspiratory muscles; pressure increases in the lungs and air is forced out
Active process during forced breathing

7. Process of Inspiration and Expiration

8. Lung Volumes Measured by Spirometry
Reprinted, by permission, from J. West, 2000, Respiratory physiology: The essentials (Baltimore, MD: Lippincott, Williams, and Wilkins), 14.

9. Pulmonary Ventilation
Key Points
Pulmonary ventilation is the process by which air is moved into and out of the lung (inspiration, expiration)
Inspiration is an active process in which the diaphragm and intercostal muscles contract, increasing dimensions and volume of the thoracic cage
Expiration at rest is normally passive; the inspiratory muscles relax, decreasing the thoracic cage
Forced inspiration and expiration are active processes involving accessory muscles
Lung volumes and capacities are measured by spirometry

10. Pulmonary Diffusion
Replenishes blood's oxygen supply that has been depleted for oxidative energy production
Removes carbon dioxide from returning venous blood

11. Blood Flow to the Lungs at Rest: Pulmonary Hemodynamics
Low pressure and resistance circulation compared to the systemic circulation
Lungs receive 4-6 L/min of blood flow
Pulmonary artery mean pressure = 15 mmHg (aortic pressure = 95 mmHg)
Left atrial pressure = 5 mmHg
Pulmonary vessels are thin walled

12. Pressures in the Pulmonary and Systemic Circulations
Reprinted, by permission, from J. West, 2000, Respiratory physiology: The essentials (Baltimore, MD: Lippincott, Williams, and Wilkins), 36.

13. Respiratory Membrane: Gas Exchange
Alveolar wall
Capillary wall
Basement membranes ( mm)
Gases will move along a concentration gradient based on partial pressures

14. Anatomy of the Respiratory Membrane

15. Partial Pressures of Air
Standard atmospheric pressure (at sea level) = 760 mmHg
Gas
Percent of Air
Partial Pressure N2
79.04%
600.7 mmHg O2
20.93%
159.1 mmHg
CO2
0.03%
0.2 mmHg

16. Partial Pressures and Gas Exchange in the Lung and Tissues

17. Fick’s Law of Diffusion
Reprinted, by permission, from J. West, 2000, Respiratory physiology: The essentials (Baltimore, MD: Lippincott, Williams, and Wilkins), 26.

19. Uneven Distribution of Blood Flow in the Lung
Reprinted, by permission, from J. West, 2000, Respiratory physiology: The essentials (Baltimore, MD: Lippincott, Williams, and Wilkins), 44.

20. Pulmonary Diffusion Key Points
Pulmonary diffusion is the process by which gases are exchanged across the respiratory membrane in the alveoli
The amount and rate of gas exchange depends on the partial pressure of each gas
Gases diffuse along a pressure gradient, moving from an area of higher pressure to lower pressure
Vgas A / T x D x (P1 - P2)
(continued) .

21. Pulmonary Diffusion (continued)
Key Points
Oxygen diffusion rate increases as you move from rest to exercise
Exercising muscle requires more oxygen for metabolism; when venous oxygen is depleted, oxygen exchange at the alveoli is facilitated due to an increased pressure gradient
The pressure gradient for carbon dioxide exchange is less than for oxygen exchange, but carbon dioxide’s membrane solubility is 20 times greater than oxygen, so CO2 crosses the membrane readily

22. Oxygen Transport
Oxygen is transported bound to hemoglobin (>98%) or dissolved in plasma (<2%)
Hemoglobin concentration largely determines the oxygen-carrying capacity of blood
Increased H+ (acidity) and temperature of a muscle favors oxygen unloading in the muscle
Oxygen carrying capacity seldom limits performance in healthy individuals

23. Oxyhemoglobin Dissociation Curve
Reprinted, by permission, from S.K. Powers and E.T. Howley, 2004, Exercise physiology: Theory and application to fitness and performance, 5th ed. (New York: McGraw-Hill Companies), 205. With permission from The McGraw-Hill Companies.

24. Effects of pH and Temperature on the Oxyhemoglobin Dissociation Curve
Reprinted, by permission, from S.K. Powers and E.T. Howley, 2004, Exercise physiology: Theory and application to fitness and performance, 5th ed. (New York: McGraw-Hill Companies), 206. With permission from The McGraw-Hill Companies.

25. Carbon Dioxide Transport
Bicarbonate ions
Muscle: CO2 + H2O → H2CO3 → H+ + HCO3-
Lung: H+ + HCO3- → H2CO3 → CO2 + H2O
Dissolved in blood plasma
Bound to hemoglobin (carbaminohemoglobin)

26. Gas Exchange Key Points
O2 is transported in the blood primarily bound to hemoglobin
Hemoglobin unloading of O2 in tissues is enhanced by:
Decreased PO2
Decreased pH
Increased temperature
Hemoglobin is ~98% saturated with oxygen, and O2 carrying capacity typically does not limit performance
CO2 is primarily transported as bicarbonate ion in the blood

27. Gas Exchange at the Muscles: Arterial–Venous Oxygen Difference

28. Oxygen Transport in the Muscle: Myoglobin
Reprinted, by permission, from S.K. Powers and E.T. Howley, 2004, Exercise physiology: Theory and application to fitness and performance, 5th ed. (New York: McGraw-Hill Companies), 207. With permission from The McGraw-Hill Companies.

29. Factors Affecting Oxygen Uptake and Delivery
1. Oxygen content of blood
2. Amount of blood flow
3. Local conditions within the muscle

30. Gas Exchange at the Muscle
Key Points
(a-v)O2 difference is the difference in the oxygen content of the arterial and mixed venous blood throughout the body
O2 delivery to the tissues depends on the O2 content in the blood, blood flow to the tissues, and local conditions
CO2 exchange at the tissues is similar to O2 exchange except CO2 leaves the muscle to be transported to the lungs -

31. Regulation of Pulmonary Ventilation
Higher brain centers
Expiratory centers
Inspiratory centers
Chemoreceptors
Mechanoreceptors in the active muscles and the lung muscles
Hypothalamic input
Conscious control

32. Central and Peripheral Regulators of Respiration