Ch 17: Mechanics of Breathing
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Transcript of Ch 17: Mechanics of Breathing
Ch 17: Mechanics of BreathingCh 17: Mechanics of Breathing
Functional division of respiratory system:• respiratory zone• conducting zone
Key Topics:Key Topics:
Structure and function of Structure and function of respiratory pumpsrespiratory pumps
Gas exchangeGas exchange with blood with blood
Role of Role of surfactantsurfactant and and pressure differences on rate pressure differences on rate of exchangeof exchange
RegulationRegulation of respiration of respiration
Functions of the Respiratory System
Oxygen exchangeOxygen exchange Air to bloodAir to blood Blood to cells Blood to cells
Carbon dioxide exchange Carbon dioxide exchange Cells to bloodCells to blood Blood to airBlood to air
Regulation of body pHRegulation of body pH
Protection of alveoliProtection of alveoli
VocalizationVocalization
Lungs: – thin walled, Lungs: – thin walled, moist exchange moist exchange surface (75 msurface (75 m2 2 ) )
Ribs & skin protectRibs & skin protect
Respiratory muscles Respiratory muscles pump airpump air
Review AnatomyExternal R
espirationCellular RespirationFig 17-1
CDAnimation
Respiratory System: Anatomy Review
Pulmonary Circulation High-flow, low-pressure High-flow, low-pressure 5 Mio Americans suffer from CHF 5 Mio Americans suffer from CHF (read (read
clinical focus p. 565)clinical focus p. 565)
Gas Laws
Air is a mix of gases:Air is a mix of gases: Dalton’s lawDalton’s law Total P = Total P = Ps of individual gases Ps of individual gases Calculate Calculate partial pressure of Opartial pressure of O22 in dry air at sea level in dry air at sea level
Gases move down their pressure gradientsGases move down their pressure gradients
Pressure-volume relationship:Pressure-volume relationship: Boyle’s law:Boyle’s law: PP11VV11 = P = P22VV22
Ventilation= Breathing= Breathing
Pulmonary function tests use spirometerPulmonary function tests use spirometer
Measure lung volumes during ventilationMeasure lung volumes during ventilation
Covered in detail in lab
The Airways: Conduction of Air from Outside to Alveoli
3 upper airway functions: _______________3 upper airway functions: _______________ Mucociliary escalator depends on secretion of watery saline Mucociliary escalator depends on secretion of watery saline
– – note:note: ______________ ______________ (genetic disease)(genetic disease)
Effectiveness of nose vs. mouth breathing Effectiveness of nose vs. mouth breathing (Respirators!)(Respirators!)
Compare to Fig. 17.8
Breathing = VentilationAir flows due to pressure gradients Air flows due to pressure gradients (analogous to blood)(analogous to blood)
InspirationInspiration:: Contraction of diaphragm (60-75%) of volume changeContraction of diaphragm (60-75%) of volume change _______ intercostals and scalenes (25-40%) _______ intercostals and scalenes (25-40%)
ExpirationExpiration Relaxation of inspiratory musclesRelaxation of inspiratory muscles Elastic recoil of pleura and lung tissue reinforce muscle Elastic recoil of pleura and lung tissue reinforce muscle
recoilrecoil
Fig17-9/11
Po = Pi Po vs Pi ? Po vs Pi ?
Fig17-9
Pressure Changes During Ventilation
Fig17-11
Alveolar and Intrapleural Pressures
Lungs unable to expand and contract on their ownLungs unable to expand and contract on their own
During development, intrapleural pressure During development, intrapleural pressure becomes subatmosphericbecomes subatmospheric
Lungs “stuck” to thoracic cage by pleural fluid Lungs “stuck” to thoracic cage by pleural fluid bondbond
Pneumothorax ?Pneumothorax ?
Fig 17-12
Pneumothorax Therapy?
Fig 17-12
Tube thoracostomy
Lung Compliance and Elastance
Compliance:Compliance: ability of lungs to stretch ability of lungs to stretch Low compliance in fibrotic lungs (and other restrictive Low compliance in fibrotic lungs (and other restrictive
lung diseases) and when not enough surfactantlung diseases) and when not enough surfactant
ElasticityElasticity (= Elastance): ability to return to (= Elastance): ability to return to original shapeoriginal shape Low Elasticity in case of emphysema due to destruction Low Elasticity in case of emphysema due to destruction
of elastic fibers.of elastic fibers.
Normal lung is both compliant AND elasticNormal lung is both compliant AND elastic
Surfactant
Surface tension at all air-fluid boundaries due to?Surface tension at all air-fluid boundaries due to? Surface tension opposes alveolar expansionSurface tension opposes alveolar expansion SurfactantSurfactant = detergent like complex of proteins & = detergent like complex of proteins &
PL: Disrupts cohesive forces between water PL: Disrupts cohesive forces between water molecules molecules surface tension surface tension work of breathing
IRDSIRDS
Unequal attraction produces tension at liquid surface
Airways Resistance Also influences work of breathing.Also influences work of breathing. Primary determinant: airway diameterPrimary determinant: airway diameter Bronchiole diameter is adjustable Bronchiole diameter is adjustable Under nervous, hormonal and paracrine Under nervous, hormonal and paracrine
controlcontrol Parasympathetic:Parasympathetic: Sympathetic:Sympathetic: Epinephrine (Epinephrine (22 receptors): receptors): Histamine:Histamine: CO CO 22
Matching Ventilation with Alveolar Blood Flow (Perfusion)
Mostly local regulation Mostly local regulation Lung has collapsible capillaries Lung has collapsible capillaries Reduced Reduced
blood flow at rest in lung apex blood flow at rest in lung apex (reserve capacity (reserve capacity of body)of body)
[CO[CO22] in exhaled air ] in exhaled air bronchodilation bronchodilation
[O[O22] in ECF around pulmonary arterioles ] in ECF around pulmonary arterioles vasoconstriction of arteriole (blood vasoconstriction of arteriole (blood diverted) – diverted) – opposite of systemic circulation!opposite of systemic circulation!
Emphysema