CARDIOVASCULAR SYSTEM CIRCULATION

Second Edition

Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings.

Human PhysiologyHuman PhysiologyPrinciples ofPrinciples of

PowerPoint® Lecture Slides Prepared by Cindy Stanfield, University of South Alabama

William J. Germann | Cindy L. Stanfield

17 The Respiratory System:The Respiratory System:Pulmonary VentilationPulmonary Ventilation


Chapter OutlineChapter Outline

I.I. Overview of Respiratory FunctionOverview of Respiratory Function

II.II. Anatomy of the Respiratory SystemAnatomy of the Respiratory System

III.III. Forces for Pulmonary VentilationForces for Pulmonary Ventilation

IV.IV. Factors Affecting Pulmonary VentilationFactors Affecting Pulmonary Ventilation

V.V. Clinical Significance of Respiratory Volumes Clinical Significance of Respiratory Volumes and Air Flowsand Air Flows


I. Overview of Respiratory FunctionI. Overview of Respiratory Function


Overview of RespirationOverview of Respiration

• Internal respiration

– Oxidative phosphorylation

• External respiration

– Exchange of oxygen and carbon dioxide between atmosphere and body tissues


External RespirationExternal Respiration

• Pulmonary ventilation

• Exchange between lungs and blood

• Transportation in blood

• Exchange between blood and body tissues


External Respiration: Ventilation and Exchange External Respiration: Ventilation and Exchange Between Lungs and BloodBetween Lungs and Blood

Figure 17.1


External Respiration:External Respiration:Transport in BloodTransport in Blood

Figure 17.1


External Respiration:External Respiration:Exchange Between Blood and TissueExchange Between Blood and Tissue

Figure 17.1


Internal RespirationInternal Respiration

Figure 17.1


II. Anatomy of the Respiratory SystemII. Anatomy of the Respiratory System

• Upper AirwaysUpper Airways

• Respiratory TractRespiratory Tract

• Structures of the Thoracic CavityStructures of the Thoracic Cavity


Upper AirwaysUpper Airways

Air passages of the head and neck

• Nasal cavity

• Oral cavity

• Pharynx


Upper AirwaysUpper Airways

Figure 17.2


Respiratory TractRespiratory Tract

Airways from pharynx to lungs

• Larynx

• Conducting zone

• Respiratory zone


Respiratory TractRespiratory Tract

Figure 17.2


Structures of the Conducting ZoneStructures of the Conducting Zone

• Trachea

• Bronchi

• Secondary bronchi

– Right side - 3 (to 3 lobes of right lung)

– Left side - 2 (to 2 lobes of left lung)


Structures of the Conducting ZoneStructures of the Conducting Zone

• Tertiary,...Bronchi

– 20-23 orders of branching

• Bronchioles

– Less than 1 mm diameter

• Terminal bronchioles


Functions of the Conducting ZoneFunctions of the Conducting Zone

• Air passageway

– 150 mL volume = dead space volume

• Increase air temperature to body temperature

• Humidify air


Epithelium of the Conducting ZoneEpithelium of the Conducting Zone

• Goblet cells – secret mucus

• Ciliated cells – cilia move particles toward mouth

• Mucus escalator


Anatomical Features of the Conducting ZoneAnatomical Features of the Conducting Zone

Figure 17.3


Photomicrograph of Tracheal EpitheliumPhotomicrograph of Tracheal Epithelium

Figure 17.4a


Structures of the Respiratory ZoneStructures of the Respiratory Zone

• Respiratory bronchioles

• Alveolar ducts

• Alveoli

• Alveolar sacs


Function of the Respiratory ZoneFunction of the Respiratory Zone

• Exchange of gases between air and blood by diffusion


Epithelium of the Respiratory ZoneEpithelium of the Respiratory Zone

• Respiratory membrane

– Epithelial cells of alveoli

– Endothelial cells of capillary


Anatomical Features of the Respiratory ZoneAnatomical Features of the Respiratory Zone

Figure 17.3


Photomicrograph of Respiratory Bronchioles Photomicrograph of Respiratory Bronchioles and Alveoliand Alveoli

Figure 17.4b


Respiratory ZoneRespiratory Zone

Figure 17.5a, b


Anatomy of AlveoliAnatomy of Alveoli

Figure 17.5c


AlveoliAlveoli

• Alveoli = site of gas exchange

• 300 million alveoli/lung (tennis court size)

• Rich blood supply- capillaries form sheet over alveoli

• Alveolar pores


AlveoliAlveoli

• Type I alveolar cells – make up wall of alveoli

– Single layer epithelial cells

• Type II alveolar cells – secrete surfactant

• Alveolar macrophages


The Respiratory MembraneThe Respiratory Membrane

Figure 17.5d


Respiratory MembraneRespiratory Membrane

• Barrier for diffusion

– Type 1 cells + basement membrane

– Capillary endothelial cells + basement membrane

• 0.2 microns thick


Scanning Electron Micrograph of Bronchiole Scanning Electron Micrograph of Bronchiole and Alveoliand Alveoli

Figure 17.5e


Resin Cast of Blood Vessels to the LungsResin Cast of Blood Vessels to the Lungs

Figure 17.6a


Scanning Electron Micrograph of Capillaries Scanning Electron Micrograph of Capillaries Around AlveoliAround Alveoli

Figure 17.6b


Structures of the Thoracic CavityStructures of the Thoracic Cavity

• Chest wall – air tight, protects lungs

– Rib cage

– Sternum

– Thoracic vertebrae

– Muscles - internal/external intercostals, diaphragm


Structures of the Thoracic CavityStructures of the Thoracic Cavity

• Pleura – membrane lining of lungs and chest wall

– Pleural sac around each lung

– Intrapleural space filled with intrapleural fluid

• Volume = 15 mL


Chest Wall and Pleural SacChest Wall and Pleural Sac

Figure 17.7


Role of Pressure in Pulmonary VentilationRole of Pressure in Pulmonary Ventilation

• Air moves in and out of lungs by bulk flow

• Pressure gradient drives flow

– Air moves from high to low pressure

– Inspiration: pressure in lungs less than atmosphere

– Expiration: pressure in lungs greater than atmosphere


III. Forces for Pulmonary VentilationIII. Forces for Pulmonary Ventilation

• Pulmonary PressuresPulmonary Pressures

• Mechanics of BreathingMechanics of Breathing


Pulmonary PressuresPulmonary Pressures

• Atmospheric pressure = Patm

• Intra-alveolar pressure = Palv

– Pressure of air in alveoli

• Intrapleural pressure = Pip

– Pressure inside pleural sac

• Transpulmonary pressure = Palv – Pip

– Distending pressure across the lung wall


Atmospheric PressureAtmospheric Pressure

• 760 mm Hg at sea level

• Decreases as altitude increases

• Increases under water

• Other lung pressures given relative to atmospheric (set Patm = 0 mm Hg)


Intra-alveolar PressureIntra-alveolar Pressure

• Pressure of air in alveoli

• Given relative to atmospheric pressure

• Varies with phase of respiration

– During inspiration = negative (less than atmospheric)

– During expiration = positive (more than atmospheric)

• Difference between Palv and Patmdrives ventilation


Intrapleural PressureIntrapleural Pressure

• Pressure inside pleural sac

– Always negative under normal conditions

– Always less than Palv

• Varies with phase of respiration

– At rest, -4 mm Hg


Intrapleural PressureIntrapleural Pressure

• Negative pressure due to elasticity in lungs and chest wall

– Lungs recoil inward

– Chest wall recoils outward

– Opposing pulls on intrapleural space

– Surface tension of intrapleural fluid hold wall and lungs together


Transpulmonary PressureTranspulmonary Pressure

• Transpulmonary pressure = Palv – Pip

• Distending pressure across the lung wall

• Increase in transpulmonary pressure:

– Increase distending pressure across lungs

– Lungs (alveoli) expand, increasing volume


Pulmonary Pressures at RestPulmonary Pressures at Rest

FRC = Functional Residual Capacity = volume of air in lungs between breaths (defined as rest); Palv = Patm

Figure 17.8


PneumothoraxPneumothorax

Figure 17.9


Mechanics of BreathingMechanics of Breathing

• Movement of air in and out of lungs due to pressure gradients

• Mechanics of breathing describes mechanisms for creating pressure gradients


Forces for Air FlowForces for Air Flow

• Force for flow = pressure gradient

• Atmospheric pressure constant (during breathing cycle)

• Therefore, changes in alveolar pressure creates/changes gradients

Patm – Palv

Flow = R


Forces for Air FlowForces for Air Flow

• Boyle’s Law: pressure is inversely related to volume

• Thus – can change alveolar pressure by changing its volume

• R = resistance to air flow

• Resistance related to radius of airways and mucus


Determinants of Intra-Alveolar PressureDeterminants of Intra-Alveolar Pressure

• Factors determining intra-alveolar pressure

– Quantity of air in alveoli

– Volume of alveoli

• Lungs expand – alveolar volume increases

– Palv decreases

– Pressure gradient drives air into lungs

• Lungs recoil – alveolar volume decreases

– Palv increases

– Pressure gradient drives air out of lungs


Changes in Intra-Alveolar Pressure Changes in Intra-Alveolar Pressure During RespirationDuring Respiration

Figure 17.10


Muscles of RespirationMuscles of Respiration

• Inspiratory muscles increase volume of thoracic cavity

– Diaphragm

– External intercostals

• Expiratory muscles decrease volume of thoracic cavity

– Internal intercostals

– Abdominal muscles


Muscles of RespirationMuscles of Respiration

• Expiration is generally passive (no muscles required)


Respiratory MusclesRespiratory Muscles

Figure 17.11a


Inspiration and ExpirationInspiration and Expiration

Figure 17.11b


Neural Control of InspirationNeural Control of Inspiration

Figure 17.12


Volume and Pressure Changes: Volume and Pressure Changes: Inspiration and ExpirationInspiration and Expiration

Figure 17.13a, b


ExpirationExpiration

• Expiration normally a passive process

– When inspiratory muscles stop contracting, recoil of lungs and chest wall to original positions decreases volume of thoracic cavity

• Active expiration requires expiratory muscles

– Contraction of expiratory muscles creates greater and faster decrease in volume of thoracic cavity


IV. Factors Affecting Pulmonary VentilationIV. Factors Affecting Pulmonary Ventilation

• Lung ComplianceLung Compliance

• Airway ResistanceAirway Resistance


Lung ComplianceLung Compliance

• Larger lung compliance

– Easier to inspire

– Smaller change in transpulmonary pressure needed to bring in a given volume of air

Ease with which lungs can be stretched

VLung Compliance =

(Palv – Pip)


Factors Affecting Lung ComplianceFactors Affecting Lung Compliance

• Elasticity

– More elastic less compliant

• Surface tension of lungs

– Greater tension less compliant


Surface Tension in LungsSurface Tension in Lungs

• Thin layer fluid lines alveoli

• Surface tension due to attractions between water molecules

• Surface tension = force for alveoli to collapse or resist expansion


To Overcome Surface TensionTo Overcome Surface Tension

• Surfactant secreted from type II cells

– Surfactant = detergent that decreases surface tension

• Surfactant increases lung compliance

– Makes inspiration easier


Factors Affecting Lung VolumeFactors Affecting Lung Volume

Figure 17.14


Airway ResistanceAirway Resistance

• As airways get smaller in diameter they increase in number, keeping overall resistance low

• Pressure gradient needed for air flow thus low

– ~1 mm Hg

• An increase in resistance makes it harder to breathe

– Pressure gradient needed for air flow > 1 mm Hg


Effects of Resistance on Required Effects of Resistance on Required Pressure GradientPressure Gradient

Figure 17.15


Factors Affecting Airway ResistanceFactors Affecting Airway Resistance

• Passive Forces

– Changes in transpulmonary pressure during respiratory cycle

• Inspiration: transpulmonary pressure increases causing airways to expand

– Tractive forces

• Inspiration: as tissue moves away from airways, they pull the airways open

• Contractile Activity of Smooth Muscle

• Mucus Secretion


Role of Bronchiolar Smooth Muscle Role of Bronchiolar Smooth Muscle in Airway Resistancein Airway Resistance

• Bronchoconstriction – smooth muscle contracts causing radius to decrease

• Bronchodilation – smooth muscle relaxes causing radius to increase

• Contractile state of bronchiolar smooth muscle under extrinsic and intrinsic controls


Extrinsic Control of Bronchiole RadiusExtrinsic Control of Bronchiole Radius

• Autonomic nervous system

– Sympathetic

• Relaxation of smooth muscle

• Bronchodilation

– Parasympathetic

• Contraction of smooth muscle

• Bronchoconstriction


Extrinsic Control of Bronchiole RadiusExtrinsic Control of Bronchiole Radius

• Hormonal Control

– Epinephrine

• Relaxation of smooth muscle

• Bronchodilation


Intrinsic Control of Bronchiole RadiusIntrinsic Control of Bronchiole Radius

• Histamine – bronchoconstriction

– Released during asthma and allergies

– Also increases mucus secretion

• Carbon dioxide – bronchodilation


Pathological States that Increase Pathological States that Increase Airway ResistanceAirway Resistance

• Asthma – caused by spastic contractions of bronchiolar smooth muscle

• Chronic obstructive pulmonary diseases – COPD


V. Clinical Significance of Respiratory V. Clinical Significance of Respiratory Volumes and Air FlowsVolumes and Air Flows

• Lung Volumes and CapacitiesLung Volumes and Capacities

• Pulmonary Function TestsPulmonary Function Tests

• Alveolar VentilationAlveolar Ventilation


SpirometrySpirometry

Method of measuring lung volumes


SpirometrySpirometry

Figure 17.16


Lung Volumes and CapacitiesLung Volumes and Capacities

Figure 17.17


Obstructive Pulmonary DiseasesObstructive Pulmonary Diseases

• Associated with increased airway resistance

• Residual volume increases (harder to expire)

• Functional residual capacity increases

• Total lung capacity increases


Restrictive Pulmonary DiseasesRestrictive Pulmonary Diseases

• More difficult for lungs to expand

• Total lung capacity decreases

• Vital capacity decreases


Pulmonary Function Tests:Pulmonary Function Tests:Forced Vital Capacity (FVC)Forced Vital Capacity (FVC)

Maximum volume inhale followed by exhale as fast as possible

• Low FVC indicates restrictive pulmonary disease


Pulmonary Function Tests:Pulmonary Function Tests:Forced Expiratory Volume (FEV)Forced Expiratory Volume (FEV)

Percentage of FVC that can be exhaled within certain time frame

• FEV1 = percent of FVC that can be exhaled within 1 second

• Normal FEV1 = 80%

– (If FVC = 4000 ml, should expire 3200 ml in 1 sec)

– FEV1 < 80% indicates obstructive pulmonary disease


Minute VentilationMinute Ventilation

Total volume of air entering and leaving respiratory system each minute

• Minute ventilation = VT x RR

• Normal respiration rate = 12 breaths/min

• Normal VT = 500 mL

• Normal minute ventilation =

– 500 mL x 12 breaths/min = 6000 mL/min


Anatomical Dead SpaceAnatomical Dead Space

• Air in conducting zone does not participate in gas exchange

• Thus, conducting zone = anatomical dead space

• Dead space approximately 150 mL


Anatomical Dead SpaceAnatomical Dead Space

Figure 17.18


Alveolar VentilationAlveolar Ventilation

Volume of air reaching gas exchange areas per minute

Alveolar Ventilation = (VT x RR) – (DSV x RR)

Normal Alveolar Ventilation =(500 mL/br x 12 br/min) – (150 mL/br X 12 br/min) =

4200 mL/min


Increasing Alveolar VentilationIncreasing Alveolar Ventilation

Can increase alveolar ventilation by increase VT or RR.Increasing VT is more effective.

Table 17.1


Summary of Minute VentilationSummary of Minute Ventilation

Figure 17.19

CARDIOVASCULAR SYSTEM CIRCULATION

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