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Chapter 16

Chapter 16. Dr. D. Washington. Respiratory Physiology. The term respiration includes three separate but related function: A. Ventilation (breathing): mechanical movement of air between nose and alveoli of the lungs

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Chapter 16

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  1. Chapter 16 Dr. D. Washington

  2. Respiratory Physiology The term respiration includes three separate but related function: A. Ventilation (breathing): mechanical movement of air between nose and alveoli of the lungs B. Gas exchange: between the air and the blood; and between the blood and tissues C. Oxygen utilization: cellular metabolism

  3. E.R. Weibel’s Model of the Human Airways (Morphometry of the Human Lung) Zone T 0 1 Trachea Bronchus Terminal bronchioles Terminal bronchioles Alveolar ducts Alveolar sacs 2 Br Conductive Zone 3 Bronchioles BL 4 TBL 17 RBL 18 Transinonal or Respiratory Zone 21 AD AS 23

  4. T P Functional Unit of the Lungs Secretory cells (type II) (Surfactant) Squamous cells (type I) Alvelus Surfactant decreases the surface tension of fluids linings the alveoli. Law of LaPlace: the distending pressure (P) in a distensible, hollow object is equal at equilibrium to the tension (T) in wall divided by the 2 principal radii of curvature of the objects (R1 and R2). Interstitium basement membranes of capillary & alveolus v Surface tension caused by the cohesive forces of water molecules Air pressure inside the alveolus

  5. Without Surfactant The clamps represent the forces of surface tension. The greater pressure on the small alveolus would cause it to collapse. With Surfactant The pressure on the small alveolus is reduced. Surfactant Effects

  6. Pressure - Volume Curve(Compliance) .50 _ .25_ Lung Vol. Change (liters) expiration inspiration -4 -5 -6 -7 +3 0 -3 -4 • Intrapleural pressure (cm H20) (pressure around the lungs) • Intrapulmonary pressure Negative pressure = subatmospheric pressure

  7. Changes in Compliance A. Decrease (increased resistance) 1. Aleolar edema: decrease caused by increase in pulmonary venous pressure 2. Atelectasis: partial or complete collapse of lungs 3. Pulmonary fibrosis: infiltration or connective tissue B. Increase (decrease resistance) 1. Age: loss of elastic tissue 2. Emphysema: destruction of alveolar tissue

  8. (vol. measured on spirometer) pump Elastic Properties of the Lungs Excised dog lung When the pressure inside the jar is reduced below atm. Pressure, the lung expands.

  9. Lung Volumes Dead space Residual volume Expiration Reserve volume Tidal volume Inspiration Reserve volume 150 ml 1,000 ml 1,000 ml 500 ml 3,000 ml

  10. Lung Capacities(combination of volumes) IRV TLC - total lung capacity VC - vital capacity IC - inspiration capacity FRC - function residual capacity IC TV TLC VC ERV FRC RV RV

  11. Inspiration Reserve volume Tidal volume Expiration Reserve volume Residual volume Lung Compartments Note: If the anatomical dead space is 150ml, and the tidal volume is 500 ml;the percentage of fresh air reaching the alveoli is 350/500 X 100% = 70%

  12. Composition of Gases at Sea Level Nitrogen & rare gases PP % Oxygen PP % CO2 PP % Water PP % Inspirated air 158 21. 0.3 0.04 8 1. 594 78 (20oC; 50%Sat.) Moist tracheal 149 19.6 0.3 0.04 47 6.2 564 74 air (saturated) Alveolar air 104 13.7 40 5.3 47 6.6 569 75 Arterial blood 100 13. 40 5.3 47 6.2 573 75 Venous blood 40 5.6 46 6.5 47 6.7 573 81 Expired air 116 15.2 29 4 47 6.2 568 75 PP = Partial Pressure

  13. Inspired Air O2 = 158 CO2 = 0.3 H20 = 8 N2 = 594 Partial Pressure in the Body Expired Air O2 = 116 CO2 = 29 H20 = 47 N2 = 568 Dead space Alveoli O2 = 104 CO2 = 40 H20 = 47 N2 = 569 Left Heart O2 = 100 CO2 = 40 H20 = 47 N2 = 573 Right Heart O2 = 40 CO2 = 46 H20 = 47 N2 = 573 Veins Arteries Capillaries O2 = 40, CO2 = 46, H20 = 47, N2 = 573

  14. Coordination of Ventilation & Perfusion The efficiency of gas exchange in the lungs is dependent on the adequacy and uniformness of ventilation and perfusion. Inspired gas and pulmonary blood flow are unevenly distributed. Ventilation-perfusion ratio inequality is the most common clinical cause of arterial hypoxemia.

  15. Ventilation-Perfusion Ratio VA/Q = 0.8 in a normal person at rest Volume of blood perfusing the lungs is 1.2 times greater than the Volume of air ventilating the lungs Coordination of Ventilation & Perfusion

  16. Pathological causes for Non- Uniform Distribution of Ventilation 1. Regional Elasticity of Changes (pulmonary fibrosis) 2. Regional Obstruction of Airways 3. Intrathoracic fluid Accumulation Coordination of Ventilation & Perfusion

  17. Coordination of Ventilation & Perfusion Pathological causes for Non- Uniform Distribution of Perfusion 1. Compression of Blood Vessels Caused by Intrathoracic P. 2. Embolism 3. Regional Vasoconstriction (ANS)

  18. Regulation of Respiration I. Intrinsic Medulla of Respiratory Center found in the brain stem

  19. Regulation of Respiration II. Extrinsic A. Chemoreceptors 1. Peripheral carotid and aortic bodies 2. Central Nervous System (Medulla) 70 - 80% main cause for change

  20. Regulation of Respiration II. Extrinsic B. The Hering-Breuer reflexes Maintains normal tidal volume. (more important in infants) 1. H-B inflation reflex 2. H-B compression reflex

  21. Respiratory Center Cortical & midbrain stimuli Pneumotaxic inhibits respiration Apneustic stimulates respiration Medullary rythmicity center Impulses torespiratory muscles glassopharyngeal & vagus Cord facillatory impulses

  22. Rhytmic Oscillation in the Respiratory Center inspiratory expiratory I E neurons neurons muscles of muscles of inspiratory expiratory

  23. D A B C Respiration neurons in Brain StemDorsal View; Cerebelium removed Parabrachials N. (pneumotaric center) Middle cerebellar peduncle Apneustic center in 4th ventrical IX All transected in A & B X Dorsal group respiratory neurons XI Ventral group respiratory neurons XII Vagi intact Vagi cut

  24. A. Above pons - regular breathing continues B. Below pneumotaxic area - inspiratory neutrons fire continuously (sustained inspriation -apneusis. However, if the vagus is intact respiration continues (effects from lungs). C. Below apneustic area - gasping type irregular respiration continues with or with our vagus D. Below medulla - respiration stops (phrenic nerve cut) Respiration neurons in Brain StemDorsal View; Cerebelium removedEffects of Transection

  25. Decreased ventilation Increased arterial Pco2 Blood pH Plasma CO2 Blood Chemoreceptors in aortic & carotid bodies CSF Chemoreceptors in medulla oblongata Respiratory center in medualla oblongata Sensory neurons Respiratory muscles Spinal cord motor neurons Negative feedback Increased ventilation

  26. Co2 ph O2 Pco235 40 45 50 55 Po2 120 100 80 60 40 ph 7.5 7.4 7.3 7.2 7.1 Effects of Po2, Pco2 + ph on Alveolar Ventilation Fluctuation of one variable at a time Alveolar Ventilation (basal rates) 7 6 5 4 3 2 1 0

  27. Co2 ph O2 Pco240 Po2 100 ph 7.4 Effects of Po2, Pco2 + ph on Alveolar Ventilation Free Fluctuation

  28. Oxygen Solubility Henry’s Law The concentration of a gas dissolved in a fluid is directly proportional to the partial pressure of that gas. Solubility Coefficients of O2 in blood = 24cc/L/atmos. Arterial Po2= 100mmHg therefore, dissolved O2 = = 3/15cc/l 100mmHg x 24cc/L 760 mmHg

  29. CH3 CH CH2 Heme C C HC C C CH N CH3 C C C CH3 C N Fe N CH2 C C C C CH2 C N C CH2 C HC CH COOH C C CH2 CH3 CH2 COOH

  30. Effect of Changes inPo2 on Blood Oxyhemoglobin Saturation and Oxygen Content (figure 15.34) Amount of O2 unloaded to Tissues 20 15 10 5 0 100 80 60 40 20 0 Percent oxyhemoglobin saturation Veins (at rest) Ozygen content (ml O2/100 ml blood) Arteries 0 20 40 60 80 100 Po2 (mm Hg)

  31. half saturations myglobin = 6mm Hg hemoglobin = 24 mm Hg O2 pressure mmHG Oxygen Dissociation hemoglobin 7% 100 80 60 40 20 0 myglobin 38% dissociated 50 % Saturation 0 20 40 60 80 100

  32. K = Oxygen Dissociation Th O2 dissociation curve for myoglobin follows the law of mass action with a dissociation constant of 3.3, the Po2 has to fall almost to 0 before the O2 is releases to the cells Mb +Po2 Mbo2

  33. pCO2 = 40 100 80 60 40 20 0 pCO2 = 80 pCO2 = 20 0 20 40 60 80 100 A drop in pH at any pO2, causes an In O2 Dissociation. Bohr Effect(effect of pH on O2 Dissociation) pCO2 = 20 high pH, shift left pCO2 = 80 low pH, shift right % O2 saturation Po2

  34. Bohr Effect(effect of pH on O2 Dissociation) Factors affecting O2 Dissociation 1. pH (or Co2 ) - deoxyhemogloblim binds H+ more actively then oxyhemogloblim 2. Temperature - effects metabolic rate [CO2] CO2+ H20 H2O H2CO3 H+ + HCO3 3. 2,3 - DPG (diphosphoglycerate) of RBC.

  35. Carbonic anhydrase CO2+ H2O H2CO3 H2CO3 H++HCO3 - H+ combines with hemoglobin CO2combined with hemogloblin to form carbaminohemoglobin (20%) Carbon Dioxide Transport the Chloride Shift in Tissue Capillaries Tissue Cells CO2 dissolved in plasma (10%) CO2 Red blood cells HCO 3 - (70%) Plasma Cl- Chloride shift

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