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Chapter 17 Mechanics of Breathing

Chapter 17 Mechanics of Breathing - Ch 17 Mechanics of...

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Unformatted text preview: Ch 17: Mechanics of Breathing Ch Functional division of respiratory system: • respiratory zone • conducting zone Key Topics: s Structure and function of respiratory pumps respiratory s Gas exchange with blood Gas s Role of surfactant and pressure surfactant differences on rate of exchange differences s Regulation of respiration Regulation Functions of the Respiratory System s Oxygen exchange x x s Carbon dioxide exchange Carbon x x s Air to blood Blood to cells (?) Cells to blood Blood to air Regulation of body pH x CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3- s Protection from pathogens, Protection irritants irritants s Vocalization Terminology s Inspiration = Inhalation s Expiration = Exhalation s Ventilation s Exchange External Respiration Fig 17-1 Cellular Respiration Review Anatomy s Lungs: – thin walled, moist Lungs: exchange surface (75 m2 ) exchange x Alveoli s Ribs & skin protect s Respiratory muscles create Respiratory the pressure gradient that moves air moves x Diaphragm x Intercostals Pulmonary Circulation s High-flow, low-pressure High-flow, s 5 x 106 Americans suffer from CHF (read clinical focus p. 565) clinical Gas Laws p 565 Partial Pressure = the pressure (in mm Hg) of a single gas in a mixture. An expression of concentration of a gas. (Chapt 18) Atmospheric Pressure = 760 mm Hg at sea level; often reported as 0 mm Hg s Air is a mix of gases: Dalton’s law Dalton’s Total P = Σ Ps of individual gases Calculate partial pressure of O2 in dry air at sea level pressure s Gases move down their pressure gradients s Pressure-volume relationship: s Boyle’s law: P1V1 = P2V2 x Describes the collisions of the gas molecules with both other gas Describes molecule and the walls of the chamber molecule Ventilation s = Breathing s Pulmonary Function Tests use Spirometer s Measure volume of air moved during Measure ventilation ventilation More Terminology s Tidal Volume: Volume moved during normal Tidal respiration respiration x s Inspiratory Reserve Volume: The additional Inspiratory volume after a tidal inspiration volume x s Approx 3000 ml Expiratory Reserve Volume: The additional Expiratory volume after a tidal expiration volume x s Approx 500 ml Approx 1100 ml Residual volume: What’s left after Residual Expiratory Reserve Volume is exhaled Expiratory x Harder to measure, approx 1200 ml Harder The Airways: Conduction of Air from Outside to Alveoli s 3 upper airway functions: upper x x Moisturizing x s Warming Warming Filtration Filtration Mucociliary escalator depends on secretion of Mucociliary watery saline – note: Cystic Fibrosis (genetic note: disease) interferes with mucus clearance disease) s Effectiveness of nose vs. mouth breathing Effectiveness (Respirators!) (Respirators!) Compare to Fig. 17.8 Breathing and Ventilation s s Air flows due to pressure gradients (analogous Air to blood) to Inspiration: x x s Contraction of diaphragm (60-75%) of volume Contraction change change External intercostals and scalenes (25-40%) External Expiration x x Relaxation of inspiratory muscles Elastic recoil of pleura and lung tissue reinforce Elastic muscle recoil muscle Flow Rate ∝ ∆ P/ R Flow Alveolar and Intrapleural Pressures Lungs unable to expand and contract on Lungs their own their During inspiration, intrapleural pressure During becomes subatmospheric Lungs “stuck” to thoracic cage by pleural fluid bond and vacuum fluid Pneumothorax? Fig 17-12 More Terminology s Compliance: ability of lungs to stretch x s Elasticity (= Elastance): ability to return to original shape to x s Low compliance in fibrotic lungs (and Low other restrictive lung diseases) and when not enough surfactant not Low Elasticity in case of emphysema due to Low destruction of elastic fibers. destruction Normal lung is both compliant AND Normal elastic elastic Surfactant Unequal attraction produces tension at liquid surface s Surface tension at all air-fluid boundaries Surface due to? due s Surface tension opposes alveolar Surface expansion expansion s Surfactant = detergent like complex of proteins & PL: Disrupts cohesive forces between water molecules ⇒ ↓ surface tension ⇒ Easier inflation of alveoli ⇒ ↓ tension work of breathing s RDS, p 576 RDS, 576 Airways Resistance s Also influences work of breathing. s Primary determinant: airway diameter x x s Tracheal diameter is not “adjustable” Bronchiole diameter is adjustable Bronchiole Under nervous, hormonal and Under paracrine control paracrine x Parasympathetic: x Sympathetic: 3 Epinephrine (β 2 receptors): x Histamine: x CO2 Matching Ventilation with Alveolar Blood Flow (Perfusion) s Mostly local regulation Mostly s Lung has collapsible capillaries ⇒ Reduced blood Lung flow at rest in lung apex (reserve capacity of body) (reserve s ↑ [CO2] iin exhaled air ⇒ bronchodilation [CO n s ↓ [O2] iin ECF around pulmonary arterioles ⇒ [O n vasoconstriction of arteriole (blood diverted) – opposite of systemic circulation! opposite ...
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