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Chapter 17

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Chapter 17

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  1. Chapter 17 Mechanics of Breathing

  2. About this Chapter • Structure and function of the respiratory pumps • How gases are exchanged with blood • The role of pressures and surfactants in rate of exchange • How respiration is regulated

  3. Respiratory System: Overview • Lungs: exchange surface • 75 m2 • Thin walled • Moist • Ribs & skin protect • Diaphragm & ribs pump air

  4. Interesting Facts about the Lungs • Each lung contains approximately 150 million alveoli • We lose half a liter of fluid a day from breathing • Normal breathing rate is between 12-16 breaths per minute, but women and children breathe faster than men • Breathing rate may to increase to 60 after exercise • The capillaries in the lung would extend approximately 1000 miles if laid end to end • Approximately 1500 miles of airways are found in the lungs • A typical sneeze travels at a velocity of 100 miles per hour • The right lung is larger than the left lung and has three lobes as compared to 2 for the left • Every minute we breathe 13 pints of air or 6.15 Liters/min • We inhale and exhale approximately 22,000 times/day

  5. Respiratory System: Overview Figure 17-2 b: Anatomy Summary

  6. Respiratory System Structure • Conduction zone: pathway for pulmonary ventilation • Respiratory zone: membrane for gas exchange  external respiration • Clinically, two parts: • Upper respiratory tract • Lower respiratory tract

  7. Cross Section Through Lung

  8. Smoker’s Lungs Non-smoker 

  9. Lung Tissue slide Respiratory Bronchiole Alveolar Duct Alveoli Alveolar Sac

  10. Functions of the Respiratory System: Overview • Exchange O2 • Air to blood • Blood to cells • Exchange CO2 • Cells to blood • Blood to air • Regulate blood pH • Vocalizations • Protect alveoli Figure 17-1: Overview of external and cellular respiration

  11. The Airways: Conduction of Air from Outside to Alveoli • Filter, warm & moisten air • Nose, (mouth), trachea, bronchi & bronchioles • Huge increase in cross sectional area Figure 17-4: Branching of the airways

  12. Key Gas Laws Reviewed • Gas is compressible & flow  with  resistance • Air is a mix of gases, each diffuses independently

  13. Key Gas Laws Reviewed • Solubility of a gas depends on: • Partial pressure of that gas (example: O2 =156 mmHg) • Temperature • Solubility in a particular solvent • Water: solvent for life • O2 into water: 0.1 m moles/L (poor) • CO2 into water: 3.0 m mole/L (good)

  14. Ventilation: The Pumps • Inspiration • Expiration • Diaphragm • Low energy pump • Concavity – flattens • Thorax: ribs & muscles • Pleura: double membrane • Vacuum seal • Fluid-lubrication

  15. Ventilation: The Pumps Figure 17-11 a: Surfactant reduces surface tension

  16. Respiratory Damage & Diseases • Pneumothorax ("collapsed lung") • Fibrotic Lung Disease • Emphysema • Chronic Bronchitis • Asthma • NRDS

  17. Pink Puffer-Emphysema is Primary Problem • A "pink puffer" is a person where emphysema is the primary underlying pathology. As you recall, emphysema results from destruction of the airways distal to the terminal bronchiole--which also includes the gradual destruction of the pulmonary capillary bed and thus decreased inability to oxygenate the blood.  So, not only is there less surface area for gas exchange, there is also less vascular bed for gas exchange--but less ventilation-perfusion mismatch than blue bloaters.  The body then has to compensate by hyperventilation (the "puffer" part).  Their arterial blood gases (ABGs) actually are relatively normal because of this compensatory hyperventilation.  Eventually, because of the low cardiac output, people afflicted with this disease develop muscle wasting and weight loss.  They actually have less hypoxemia (compared to blue bloaters) and appear to have a "pink" complexion and hence "pink puffer".  Some of the pink appearance may also be due to the work (use of neck and chest muscles) these folks put into just drawing a breath.

  18. Blue Bloater-Chronic Bronchitis is Primary Problem • A "blue bloater" is a person where the primary underlying lung pathology is chronic bronchitis. Just a reminder, chronic bronchitis is caused by excessive mucus production with airway obstruction resulting from hyperplasia of mucus-producing glands, goblet cell metaplasia, and chronic inflammation around bronchi.  Unlike emphysema, the pulmonary capillary bed is undamaged. Instead, the body responds to the increased obstruction by decreasing ventilation and increasing cardiac output. There is a dreadful ventilation to perfusion mismatch leading to hypoxemia and polycythemia.  In addition, they also have increased carbon dioxide retention (hypercapnia).  Because of increasing obstruction, their residual lung volume gradually increases (the "bloating" part).  They are hypoxemic/cyanotic because they actually have worse hypoxemia than pink puffers and this manifests as bluish lips and faces--the "blue" part. • Link to website detailing pathophysiology of emphysema and chronic bronchitis is listed below: http://www.pathophys.org/copd/#Pathogenesis_pathophysiology_and_clinical_features

  19. Respiratory Damage & Diseases Figure 17-11b: Surfactant reduces surface tension

  20. Factors Affecting Ventilation • Airway Resistance • Diameter • Mucous blockage • Bronchoconstriction • Bronchodilation • Alveolar compliance • Surfactants • Surface tension • Alveolar elasticity Figure 17-2e: Anatomy Summary

  21. Lung Volumes: Spirometer Measurements Figure 17-12: The recording spirometer

  22. Spirometry

  23. Efficiency of Breathing: Normal & High Demand • Total Pulmonary Ventilation (rate X tidal vol about 6 L/min) • Alveolar ventilation (– dead air space – 4.5 L/min) • Little variation [O2] & [CO2] • Exercise- High Demand •  Depth of breathing • Use inspiratory reserve

  24. Efficiency of Breathing: Normal & High Demand Figure 17-14: Total pulmonary and alveolar ventilation

  25. Mucociliary Escalator Figure 17-6: Ciliated respiratory epithelium

  26. Gas Exchange in the Alveoli • Thin cells: exchange • Surfactant cells • Elastic fibers • Recoil • Push air out • Thin basement membrane • Capillaries cover 90% of surface

  27. Gas Exchange in the Alveoli Figure 17-2 h : Anatomy Summary

  28. Gas ExchangeExternal Respiration • The exchange membrane components and organization

  29. Capillaries in Alveolar Wall

  30. PCO2 = 46 mm Hg PO2 = 40 mm Hg PO2 = 100 mm Hg inspired air PCO2 = 40 mm Hg PO2 = 40 mm Hg expired air PCO2 = 46 mm Hg PO2 = 100 mm Hg PCO2 = 40 mm Hg Gas ExchangeExternal Respiration arteriole end O2 pulmonary capillary alveolus CO2 venule end

  31. PCO2 = 40 mm Hg PO2 = 100 mm Hg PO2 = 40 mm Hg PCO2 = 46 mm Hg PO2 = 100 mm Hg PCO2 = 40 mm Hg PO2 = 40 mm Hg PCO2 = 46 mm Hg Gas ExchangeInternal Respiration arteriole end O2 systemic capillary systemic cell CO2 venule end

  32. Gas Exchange • What happens when alveolar PO2 drops? • Solubility rules indicate that • If PO2 drops, then the amount dissolved in blood also drops! • Creating a hypoxic condition • Factors that may cause low arterial PO2 • Not enough O2 reaching alveoli • Exchange between alveoli and pulmonary capillaries has a problem • Not enough O2 transported in blood

  33. Matching Ventilation with Alveolar Blood Flow (Perfusion)---How does the lung match ventilation with perfusion? • Mostly local regulation using CO2 to control bronchiolar dilation and O2 to control arteriolar dilation • Low [O2] in alveoli  vasoconstriction of arteriole • Reduced blood flow at rest • (lung apex ) • saves energy • High blood [CO2]  bronchodilation