Chapter 13 – Part 3 The Respiratory System

1. Chapter 13 – Part 3The Respiratory System

2. Events of Respiration • The major function of the respiratory system is to supply the body with O2 and to dispose of CO2. • To do this, at least four events must occur (collectively called respiration): • Pulmonary ventilation • External respiration • Respiratory gas transport • Internal respiration

3. Events of Respiration • Pulmonary ventilation – moving air in and out of the lungs • Commonly called breathing • External respiration – gas exchange between pulmonary blood and alveoli • O2 loading and CO2 unloading

4. Events of Respiration Respiratory gas transport – transport of oxygen and carbon dioxide via the bloodstream to and from the lungs and body tissues Internal respiration – gas exchange between blood and tissue cells in systemic capillaries

5. Mechanics of Breathing (Pulmonary Ventilation) • Completely mechanical process • Depends on volume changes in the thoracic cavity

6. Mechanics of Breathing (Pulmonary Ventilation) • Volume changes lead to pressure changes, which lead to the flow of gases to equalize pressure • A gas always conforms to the shape of its container • In a large volume, the pressure will be low. • If the volume is reduced, the gas molecules will be closer together and the pressure will rise.

8. Mechanics of Breathing (Pulmonary Ventilation) • Two phases • Inspiration – flow of air into the lungs • Expiration – air leaving the lungs

9. Inspiration (Inhalation) • Diaphragm and intercostalmuscles contract resulting in the increased size of the thoracic cavity • As the diaphragm contracts, it moves inferiorly and flattens out • Contraction of the intercostals lifts the rib cage and thrusts the sternum forward

10. Inspiration (Inhalation) • The increased volume results in a decreased gas pressure within the lungs, which produces a partial vacuum • External air is pulled into the lungs due to an increase in intrapulmonary volume • Air continues to pull into the lungs until the intrapulmonary pressure equals the atmospheric pressure.

11. Inspiration (Inhalation)

12. Exhalation (Expiration) • Largely a passive process which depends on natural lung elasticity • As muscles relax, air is pushed out of the lungs • Forced expiration can occur mostly by contracting internal intercostal muscles to depress the rib cage

13. Exhalation (Expiration)

14. Pressure Differences in the Thoracic Cavity • Normal pressure within the pleural space (intrapleural pressure) is always negative • Differences in lung and pleural space pressures keep lungs from collapsing • If for any reason, the intrapleural pressure becomes equal to the atmospheric pressure, the lungs will collapse

15. Atelectasis • Atelectasis – lung collapse • The lung is useless for ventilation • Usually occurs when air enters the pleural space from: • A chest wound • A rupture of the visceral pleura • Is reversed by drawing air out of the intrapleural space with chest tubes, which allows the lungs to re-inflate and resume its normal function

16. Nonrespiratory Air Movements • Can be caused by reflexes or voluntary actions • Examples • Cough - Clears the lower respiratory passages of debris • Sneeze – Clears the upper respiratory passages of debris • Laughing • Crying • Yawn – Increases ventilation to the lungs; May be initiated by a need to increase oxygen levels in the blood • Hiccup – Sudden inspiration; Results from spasms of the diaphragm

17. Respiratory Volumes and Capacities • Tidal volume (TV)– Amount of air inhaled of exhaled with a normal breath • Normal breathing moves about 500 ml of air (about a pint) with each breath • Many factors that affect respiratory capacity • A person’s size • Sex • Age • Physical condition

18. Respiratory Volumes and Capacities • Inspiratory reserve volume (IRV) -Amount of air that can be taken in forcibly over the tidal volume • A person can inhale much more air than is taken in during a normal, or tidal, breath • Usually between 2100 and 3200 ml

19. Respiratory Capacities

20. Respiratory Volumes and Capacities • Expiratory reserve volume (ERV) - Amount of air that can be forcibly exhaled • After a normal expiration, more air can be exhaled • Approximately 1200 ml

21. Respiratory Volumes and Capacities • Residual volume - Air remaining in the lungs after expiration • Even after the most strenuous expiration, about 1200 ml of air still remains in the lungs • The residual volume cannot be voluntarily expelled • Is important because: • It allows gas exchange to go on continuously even between breaths • It helps to keep the alveoli open (inflated)

22. Respiratory Capacities

23. Respiratory Volumes and Capacities • Vital capacity - the total amount of exchangeable air • Vital capacity = TV + IRV + ERV • Typically around 4800 ml in healthy young males

24. Respiratory Volumes and Capacities • Dead space volume - Air that remains in conducting zone and never reaches alveoli • About 150 ml in a normal tidal breath • Functional volume - Air that actually reaches the respiratory zone and contributes to gas exchange • Usually about 350 ml

25. Respiratory Volumes and Capacities • Respiratory capacities are measured with a spirometer • As a person breathes, the volumes of air exhaled can be read on an indicator • Spirometer testing is useful for evaluating losses in respiratory functioning and in following the course of some respiratory diseases