Lecture 15_Respiration mechanics.pptx

1 2 The key functions of the respiratory system: • Exchange of gases between the atmosphere and the blood • Homeostatic regulation of body pH (7.35 – 7.45)– see equation below • Protection of the respiratory membrane from inhaled pathogens and irritating substances • Speech also smell metabolism...

1 2 The key functions of the respiratory system: • Exchange of gases between the atmosphere and the blood • Homeostatic regulation of body pH (7.35 – 7.45)– see equation below • Protection of the respiratory membrane from inhaled pathogens and irritating substances • Speech also smell metabolism of circulating substances (e.g. ACE) assisting venous return to heart (remember "respiratory pump") water and heat loss Carbonic acid “Bicarb” equation: CO2 + H2O  H2CO3  H+ + HCO33 1 2 3 4 4 Silverthorn Figure 17-1 5 Figure 17.2b (what some call “respiratory zone”) Silverthorn Figure 17.4 6 Silverthorn Figure 17-5 • Goblet cells • Ciliated epithelial cells 7 Germann 17.3 8 Alveolar Structure Germann 17.5 Like Silverthorn 17.2g An alveolus is ~300 um in diameter A Typical type I cell is ~0.2 um thick Widmaier 13-3; Like Silverthorn 17.2f The typical distance between the air 9 and inside a capillary is <1 um An alveolus is ~300 um in diameter A Typical type I cell is ~0.2 um thick The typical distance between the air and inside a capillary is <1 um Silverthorn 17.2g,h Widmaier 13-4 10 Pulmonary circulation - Because the right ventricle does not contract as powerfully as the left ventricle and resistance in the pulmonary circulation is low, pressure in the pulmonary circulation tends to be low (25/8 mm Hg; systolic/diastolic). As a result, the hydrostatic pressure in lung capillaries is low, and little fluid tends to leave the circulation in the lungs. This is a useful adaptation, as a minimization of fluid in the interstitial space acts to facilitate gas exchange. Widmaier 13-6 14 Respiratory Muscles (these are voluntary, skeletal muscles) Accessory muscles of inspiration Internal intercostal muscles Sternocleidomastoid Scalenus (Scalenes) Muscles of active expiration Sternum Ribs External intercostal muscles Diaphragm Major muscles of inspiration Abdominal muscles Sherwood Figure 13.11 11 The Pleural Sac: Widmaier Fig. 13-5 12 Lungs have elastic properties! Importance of pleural fluid! 13 Germann 17.7 & 17.8 Mechanics of gas exchange Four gas principles: 1) Dalton's law: the total pressure of a mixture of gases is the sum of the pressures of the individual gases. [Atmospheric pressure at sea level is 760 mm Hg, so if nitrogen is 78% of air, then the partial pressure exerted by nitrogen is 760 * 0.78 =593 mm Hg. Oxygen comprises 21% of air, so the partial pressure exerted by oxygen is 0.21*760=160 mm Hg.] 2) Gases move from regions of high pressure to regions of low pressure. This applies to a mixed gas, and to a single gas (that moves from a region of higher partial pressure to a region of lower partial pressure). 3) Boyle's law: If the volume of a container of gas changes, the pressure of gas will change in an inverse manner (e.g., if volume expands, pressure falls; if the volume contracts, the pressure increases) . 4) The amount of gas that will dissolve in a liquid is determined by the partial pressure of the gas (you can view this as its concentration), the solubility of the gas, and the temperature. 15 At the end of expiration (i.e., you just finished exhaling): No air flow = no pressure gradient Atmosphere 760 mm Hg Airways Atmospheric pressure Thoracic wall Intra-alveolar pressure Plural wall Lungs Intrapleural pressure 756 mm Hg (Note: understand why this pressure is less than atmospheric ) 16 Sherwood figure 13.6 F = Patm - Palv / R Germann 17.10 18 F = (Patm-Palv) / R Important slide! Silverthorn Figure 17.9 20 Here is another version of the previous slide Widmaier 13-13 21 Expiration: • Passive: elastic recoil, intercostal and diaphragm relaxation of external • Active: contraction of internal intercostal and abdominal muscles 22 Compliance • Intrinsic elastic properties • Surface tension (surfactant) Widmaier 13-16 23 24 25 Siverthorn Figure 17.11 Impact of increased airway resistance What might influence resistance? Germann 17.15 26 Normal breathing represents ~3% of the total energy usage of the body. However, increasing resistance or decreasing compliance would increase the amount of energy required for breathing. In severe cases of obstructive lung disease, breathing might can account for >30% of energy usage by the body. 27 This is a different version of the next slide. The bottom half of this slide has nice definitions of the different respiratory volumes. But I like the figure on the next slide better so we will walk through these values there. Note some values are not identical but are close. 29 28 Silverthorn Figure 17.7b Importance of dead space Germann 17.18 30 Minute ventilation = Tidal volume * Respiration rate Minute alveolar ventilation = (Tidal volume – dead space) * Respiration rate 31 Germann 17.19 32