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Unit Seven: Respiration

Unit Seven: Respiration. Chapter 37: Pulmonary Ventilation. Guyton and Hall, Textbook of Medical Physiology, 12 edition. Respiration. Four Major Functions of Respiration Pulmonary ventilation Diffusion of oxygen and carbon dioxide between the alveoli and the blood

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Unit Seven: Respiration

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  1. Unit Seven: Respiration Chapter 37: Pulmonary Ventilation Guyton and Hall, Textbook of Medical Physiology, 12 edition

  2. Respiration • Four Major Functions of Respiration • Pulmonary ventilation • Diffusion of oxygen and carbon dioxide between the alveoli and the blood • Transport of oxygen and carbon dioxide in the blood and body fluids • Regulation of ventilation

  3. Mechanics of Pulmonary Ventilation • Muscles That Cause Lung Expansion and Contraction • Lungs can be expanded and contracted in two ways: • By downward and upward movement of the diaphragm • to lengthen and shorten the chest cavity • By elevation and depression of the ribs to increase and • decrease the anteroposterior diameter of the chest • cavity

  4. Mechanics of Pulmonary Ventilation Fig. 37.1 Contraction and expansion of the thoracic cage during expiration and inspiration

  5. Mechanics of Pulmonary Ventilation (cont.) • Normal quiet breathing is accomplished almost • entirely by movement of the diaphragm • During inspiration, contraction of the diaphragm • pulls the lungs downward • During expiration, the diaphragm simply relaxes, • and the elastic recoil compresses the lungs and • expels the air

  6. Mechanics of Pulmonary Ventilation (cont.) • During heavy breathing the elastic forces are not • powerful enough, so extra force is generated by • the abdominal muscles • Muscles that raise the rib cage are the external • intercostals (most important), sternocleidomastoid, • anterior serratus, and scalenes • Muscles that pull the rib cage downward during • expiration are the abominal rectus, and the internal • intercostals

  7. Mechanics of Pulmonary Ventilation (cont.) • Pressures That Cause the Movement of Air In and • Out of the Lungs • Pleural pressure- pressure of the fluid in the thin • space between the lung pleura and the chest pleura; • there is a slight suction so the pressure is negative • Alveolar pressure- pressure of the air inside the lung • alveoli • Transpulmonary pressure- difference between the • pleural and alveolar pressures (recoil pressure)

  8. Fig. 37.2 Changes in lung volume, alveolar pressure, pleural pressure, and transpulmonary pressure during normal breathing

  9. Mechanics (cont.) • Compliance of the Lungs- the extent to which the • lungs will expand for each unit increase in • transpulmonary pressure • Compliance Diagram of the Lungs • Inspiratory compliance curve • Expiratory compliance curve • Characteristics of the diagrams are dependent on • Elastic forces of the lung tissue • Elastic forces caused by surface tension of the • fluid that lines the inside walls of the alveoli

  10. Mechanics (cont.) Fig. 37.3 Compliance diagram in a healthy person Fig. 37.4 Comparison of the compliance of saline and air-filled lungs when the alveolar pressure is maintained at atmospheric pressure and pleural pressure is changed

  11. Mechanics (cont.) • Surfactant, Surface Tension, and Collapse of the Alveoli • Principle of Surface Tension-when water forms a surface • with air, the water molecules on the surface of the water • have an especially strong attraction for one another. As a • result, the water surface is always trying to contract. • Surfactant-surface active agent that reduces the surface • tension of water; secreted by Type II alveolar cells

  12. Mechanics (cont.) • Effect of the Thoracic Cage on Lung Expansibility • Compliance of the thorax and the lungs • Work of breathing (3 fractions) • Compliance or elastic work • Tissue resistance work • Airway resistance work

  13. Pulmonary Volumes and Capacities • Recording Changes in Pulmonary Volume-Spirometry Fig. 37.5 Spirometer

  14. Pulmonary Volumes and Capacities • Pulmonary Volumes • Tidal Volume (TV)-amount of air inspired or expired • with each normal breath; usually about 500 ml • Inspiratory Reserve Volume (IRV)-extra volume that can be inspired over and above the TV; usually about 3000 ml • Expiratory Reserve Volume (ERV)-max extra volume that can be expired at the end of a normal TV; usually about 1100 ml

  15. Pulmonary Volumes and Capacities • Pulmonary Volumes (cont.) • Residual Volume (RV)-amount of air remaining in the lungs after the most forceful expiration; usually about 1200 ml • Pulmonary Capacities • Inspiratory Capacity- (TV + IRV); about 3500 ml • Functional Residual Capacity- (ERV + RV); about • 2300 ml

  16. Pulmonary Volumes and Capacities • Pulmonary Capacities (cont.) • Vital Capacity (VC)- (IRV + TV + ERV); usually about • 4600 ml • d. Total Lung Capacityi (VC + RV); usually about 5800 ml

  17. Pulmonary Volumes and Capacities Fig. 37.6 Diagram showing pulmonary volumes and pulmonary capacities

  18. Minute Respiratory Volume • Minute Respiratory Volume- total amount of new air moved into the respiratory passages each minute • Equal to the TV x Respiratory Rate • Usually 500ml x 12 bpm = 6 L/min

  19. Alveolar Ventilation • Effect of “Dead Space” – air that does not reach the gas exchange areas but simply fill respiratory passages where gas exchange does not occur (dead air space) • Rate of Alveolar Ventilation- alveolar ventilation per minute is the total volume of new air entering the alveoli each minute

  20. Functions of the Respiratory Passages Fig. 37.8 Respiratory passages

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