Functions of the Respiratory System

1. Functions of the Respiratory System • Gas Exchange • Regulation of blood pH • Voice production • Olfaction • Protection

2. Tracheobronchial Tree • Conducting Zone • Respiratory Zone • Alveoli • Type I pneumocytes • Type II pneumocytes

4. Thoracic Wall & Muscles of Respiration • Thoracic wall • Thoracic vertebrae • Ribs • Sternum • Muscles • Thoracic cavity • Thoracic wall & Diaphragm

5. Thoracic Wall & Muscles of Respiration • Muscles of Respiration • Muscles of Inspiration • Diaphragm • External intercostals • Pectoralis minor • Scalenes • Muscles of Expiration • Abdominal muscles • Internal intercostals

6. Pleura • Each lung is surrounded by a separate pleural cavity. • Parietal pleura • Covers the inner layer of the throacic wall. • Visceral pleura • Covers the surface of the lung. • Pleural Cavity • Filled with pleural fluid.

8. Pleural Fluid • Acts as lubricant allowing parietal and visceral • Helps hold the parietal and visceral pleural membranes together.

9. Blood Supply • Blood that has passed through the lungs and picked up oxygen is called oxygenated blood. • Blood that has passed through the tissues and released some of its oxygen is called deoxygenated blood.

10. Ventilation • Moving air in & out of the lungs. • Flow of air into the lungs requires a pressure gradient from the outside of the body to the alveoli. • If air needs the flow out of the lungs, a pressure gradient needs to exist in the other direction. • F = (P1 – P2) / R

11. Pressure & Volume • General gas law • P = nRT / V • n, R, and T are all constants, therefore pressure is inversly proportional to volume. • Called Boyle’s Law.

12. Airflow into & out of Alveoli • Inspiration • Initiated by contraction of diaphragm & external intercostal muscles. • Result: increase in the size of the thorax. • Leads to a drop in alveolar pressure (Boyle’s Law). • Palv < PB • Lung will expand.

14. Airflow into & out of Alveoli • Expiration • At the end of inspiration, the nerves to the diaphragm and external intercostals stop firing. • These muscles relax. • Lungs & chest wall passively return to their original dimensions.

15. Airflow into & out of Alveoli • Expiration • As lungs decrease in size, the pressure increases (Boyle’s Law). • Palv > PB • Air will flow from the alveoli to the atmosphere.

17. Forced Expiration • During exercise, the expiration of larger volumes is achieved by the contraction of the internal intercostals and the abdominal muscles.

19. Lung Compliance • Compliance = “stretchability”. • Two determinants: • Compliance (stretchability of lung tissue) • Surface tension at the air-water interface of the alveoli. • Surfactant

20. Respiratory Distress Syndrome • 2nd leading cause of death in premature infants. • Normal maturation of surfactant-synthesizing cells is facilitated by hormones (particularly cortisol). • Secretion of cortisol increases late in pregnancy (7th month).

21. Respiratory Distress Syndrome • Premature babies lack mature type II alveolar cells due to low levels of cortisol. • Treatment: • Administration of cortisol to mother. • Administer high pressure, oxygen-rich air to infant. • Exogenous source of surfactant to infant.

22. Pleural Pressure • Normally lower than the alveolar pressure. • This helps keep the alveoli expanded. • If this difference is lost the alveoli will collapse. • e.g. Pneumothorax

24. Airway Resistance • F = ΔP / R • Factors that affect R: • Viscosity • Length • Radius

25. Airway Resistance • Factors that affect radius: • Transpulmonary pressure: • Exerts a distending force. • Increases during inspiration. • Lateral traction: • Connective tissue fibers pulling outwards. • Mucus Accumulation

26. Airway Resistance • Factors that affect radius: • Parasympathetic nerves • Constriction (ACh) • Epinephrine • Dilates • Histamine • Constricts

27. Asthma • Attacks are characterized by smooth muscle contraction. • Increases resistance impairing ventilation. • More mucus may also be secreted. • Main defect is inflammation of the airways. • Cause of inflammation varies from person to person (virus, allergy, etc.).

28. Asthma • Smooth muscle can be hyperresponsive to: • Exercise • Emotional stress • Cold air • Cigarette smoke • Irritants • Certain drugs

29. Asthma • Therapy: • Anti-inflammatory drugs • Bronchodilators

30. Chronic ObstructivePulmonary Disease • Examples: • Emphysema & Chronic Bronchitis • Emphysema • Destruction of alveolar walls. • Impairs gas exchange. • Destruction of elastic tissue also contributes to airway collapse (obstruction).

31. Chronic ObstructivePulmonary Disease • Examples: • Emphysema & Chronic Bronchitis • Chronic Bronchitis • Characterized by excessive mucus production in bronchi. • Results in obstruction.

32. Pulmonary Volumes & Capacities • Spirometry is the process of measuring volumes of air moving in & out of the lungs. • Important volumes • Tidal volume • Inspiratory reserve volume • Expiratory reserve volume • Residual volume

33. Pulmonary Volumes & Capacities • Spirometry is the process of measuring volumes of air moving in & out of the lungs. • Important capacities (= sum of two or more lung volumes) • Inspiratory capacity • Functional residual capacity • Vital capacity • Total lung capacity

36. Pulmonary Volumes & Capacities • Forced expiratory vital capacity is a simple clinical pulmonary test. • Forced expiratory volume in one second(FEV1) is also an important diagnostic value. • Airway obstructions (asthma, emphysema, chronic bronchitis, etc) cause a decreasedFEV1.

37. Alveolar Ventilation • Pulmonary Ventilation • VP = f (VT) • During inspiration, a portion of the inspired air fills the anatomic dead space before reaching the alveoli. • This air is not available for gas exchange. • VA = f (VT – VD)

38. Principles of Gas Exchange • Dalton’s Law • Partial Pressure • Nitrogen (78.62%) • Oxygen (20.84%) • Sea level • Total atmospheric pressure = 760 mmHg • Partial pressure of nitrogen = 597.5 mmHg • Partial pressure of oxygen = 158.4 mmHg

39. Inspired air vs. Alveolar air • Inspired air and alveolar air are different. • Air entering repiratory system is humidified. • Oxygen diffuses from alveoli into the blood. • Carbon dioxide diffuses from pulmonary capillaries into the alveoli. • Air in the alveoli is only partially replaced with atmospheric air during each inspiration.

40. Diffusion of GasesThrough Respiratory Membrane • Influenced by: • Thickness of the membrane. • Diffusion coefficient of the gas. • Surface area of the membrane (70 m2). • Difference of the partial pressures of the gas on either side of the membrane.

41. Oxygen & Carbon DioxideTransport in the Blood • Oxygen • Po2 in alveoli is approx. 104 mmHg. • Po2 in blood in pulmonary capillaries is approx.40 mmHg. • Therefore, O2 diffuses from the alveoli to the pulmonary capillaries.

42. Oxygen & Carbon DioxideTransport in the Blood • Oxygen • Equilibrium is achieved during the first third of the pulmonary capillary beds. • Blood leaving the lungs in the pulmonary veins has a Po2 of approx. 95 mmHg due to mixing with bronchial veins. • At the tissues, the Po2 is close to 40 mmHg in the interstitial space and approx. 20 mmHg in the individual cells.

43. Oxygen & Carbon DioxideTransport in the Blood • Carbon Dioxide • CO2 is continually produced during cellular respiration. • The intracellular Pco2 is approx. 46 mmHg • Interstitial Pco2 is approx. 45 mmHg • Arterial Pco2 is close to 40 mmHg • Venous Pco2 is approx. 45 mmHg • Because the Pco2 is approx. 40 mmHg in the alveoli, CO2 will diffuse into the alveoli.

45. Hemoglobin & Oxygen Transport • Approx. 98.5% of oxygen transported in the blood is combined with hemoglobin. • The other 1.5% is dissolved in the plasma. • Effect of Po2 on oxygen transport. • Oxygen-hemoglobin dissociation curve

48. Hemoglobin & Oxygen Transport • Effect of pH, Pco2, & temperature on oxygen transport. • pH • Bohr Effect: Decreases in blood pH results in an decreased ability of Hb to bind to oxygen (decreased affinity) and vice versa. • Pco2 • Increases in Pco2 decreases the ability of Hb to bind to oxygen (decreased affinity) because of the effect of CO2 on pH and vice versa.

49. Hemoglobin & Oxygen Transport • Effect of pH, Pco2, & temperature on oxygen transport. • Temperature • Increases in temperature decreases the tendency for oxygen to remain bound to Hb (decreased affinity).