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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 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 Compliance diagram in a healthy person Fig 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 Spirometer

14 Pulmonary Volumes and Capacities
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 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 Respiratory passages

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