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Anatomy and Physiology for EngineersSlide 11-1

The Respiratory System

Functions:Moves air to and from the gas-exchange sites wherediffusion occurs between air and circulating blood.Provides non-specific defenses against pathogenicinvasion.Permits vocal communication.Helps control pH of body fluids.

Anatomy and Physiology for EngineersSlide 11-2

Organization of the Respiratory System

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Anatomy and Physiology for EngineersSlide 11-3

Nose, Nasal Cavities and Pharynx

Air enters through nostrils, communicates to nasal cavity.Nasal septum divides nose into left and right sides.Nasal conchae: ridges within nasal cavity.

Produces disturbances in air flow, enhancing mixing and filtration.Respiratory epithelium: ciliated cell layer (goblet cells and mucousglands).

Cilia sweep debris and pathogens into pharynx (throat).Nasal cavity also flushed by mucus produced by nasal sinuses and bytears through nasolacrimal duct.

Anatomy and Physiology for EngineersSlide 11-4

Pharynx (throat)

Throat is shared by digestive and respiratory tracts.Dense concentration of ciliated cells.Cystic fibrosis:

Genetic disorder (chromosome 7).Bacterial infection and associated heart failure.Mucus becomes too viscous to be transported by cilia.

Leads to frequent bacterial infections.

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Anatomy and Physiology for EngineersSlide 11-5

The Larynx (Voice Box)

Incoming air leaves pharynx through glottis (narrowopening protected by larynx).3 large cartilages support larynx.

Epiglottis prevents entry of liquids or solid food into respiratorysystem.Thyroid cartilage protects anterior and lateral surfaces of larynx.

“Adam’s Apple”Cricoid cartilage provides posterior support to larynx.

Two pairs of ligaments extend across larynx betweenthyroid cartilage and 3 smaller cartilages.

False and true vocal cords.

Anatomy and Physiology for EngineersSlide 11-6

The Larynx (Voice Box)

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Anatomy and Physiology for EngineersSlide 11-7

The Trachea (Windpipe)

Anatomy and Physiology for EngineersSlide 11-8

The Bronchi and Bronchioles

Trachea branches into right and left bronchi.Bronchi are histologically similar to trachea.Rapid branching.

~ 1 mm -> bronchioles.Bronchioles parallel arterioles in function.

Varying diameter controls local flow.Sympathetic stimulation causes relaxation of smooth muscles aroundbronchioles.

Last part: terminal bronchioles (0.3 -0.5 mm diameter)Each terminal bronchiole supplies air to a lobule of the lung.

Lobule: segment of lung tissue bound by connective tissue partitions,supplied by a single terminal bronchiole, and accompanied bypulmonary arteries and veins.

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Anatomy and Physiology for EngineersSlide 11-9

Alveolar Ducts and AlveoliRespiratory bronchioles openinto alveolar ducts.Alveolar ducts end at alveolarsacs (alveoli).Gas exchange occurs at alveolisurfaces.Each lung: 150 x 106 alveoli.Alveolar surface ~ 140 m2.

Thin squamous epithelium.Alveolar macrophagesconsume dust particles.Surfactant cells releasesurfactant -> decrease surfacetension (prevents collapse ofalveolar walls.)

Anatomy and Physiology for EngineersSlide 11-10

The Respiratory MembraneGas exchange occurs across this membrane.3 components:

Squamous epithelial cells lining the alveoli.Endothelial cells lining adjacent capillary.Fused basement membranes between alveolar and endothelial cells.

Diffusion across membrane is rapid:Diffusion distances are small (thickness: ~ 0.1 µ).Both O2 and CO2 are lipid soluble.

PneumoniaDevelops due to pathogenic infection of lobule.Infection --> inflammation --> fluid leaks into alveoli --> respiratory functiondecreases.Bacterial infection usually involves bacteria normally found in lining of upperrespiratory tracts.Retardation of pathogenic defense system in these tracts (smoking, immunecompromise) allows bacteria to evade defense system and migrate intoalveoli.

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Anatomy and Physiology for EngineersSlide 11-11

The Lungs

Anatomy and Physiology for EngineersSlide 11-12

The Pleural Cavities

Thoracic cavity is the shape of a broad cone: base is thediaphragm; walls are rib cage; apex is entrance to respiratory& digestive tracts.

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Anatomy and Physiology for EngineersSlide 11-13

Respiratory Physiology

Process of respiration involves 4 key steps:Pulmonary ventilation (breathing - convection).Gas diffusion across respiratory membrane(diffusion).Storage and transport of oxygen and carbondioxide (convection).Exchange of oxygen and carbon dioxide betweenblood and interstitial fluids (diffusion).

Anatomy and Physiology for EngineersSlide 11-14

Pressure-Volume Relationship During Ventilation

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Anatomy and Physiology for EngineersSlide 11-15

Gas Exchange at the Respiratory MembraneProcess of gas exchangedepends on:

Partial pressures of O2 andCO2.

Portion of pressurecontributed by each gas.Ex: atmospheric pressure:PN2 + PO2 + PH2O + PCO2O2 ~ 21% of atmosphericgas -> PO2 ~ 20% 760 mmHg = 159 mm Hg.

Diffusion from gas into liquid& vice-versa.

Anatomy and Physiology for EngineersSlide 11-16

O2 & CO2 Pickup and Delivery

O2 and CO2 have very limited solubility in plasma~1.5% of O2 molecules found in solution. ~ 7% of CO2 in solution.

Remaining O2 transported by binding onto ironatoms of the hemoglobin (Hb) molecule.

Hb + O2 ¤ HbO2

Release of O2 from Hb molecule depends on PO2 insurrounding tissue, pH, temperature.CO2 binds to globin portion of Hb (~23%).

Remaining transported by conversion to carbonic acid(H2CO3 ¤ H+ + HCO-

3).

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Anatomy and Physiology for EngineersSlide 11-17

Control of RespirationRespiratory centers: 3 pairs of loosely organized nuclei inreticular formation of pons and medulla.

Control respiratory rate and intensity.

Inspiration

(2 seconds)

InspiratoryMusclescontract

Inspiration

Occurs

DoralRespiratory

GroupActive

PassiveExpiration

Occurs

InspiratoryMusclesRelax

DoralRespiratory

GroupInhibitedQUIET

RESPIRATION

InspiratoryMusclescontract

ExpiratoryMusclesRelax

Inspiration

Occurs

DoralRespiratory

GroupActive

VentralRespiratory

GroupInhibited

ActiveExpiration

Occurs

InspiratoryMusclesRelax

ExpiratoryMusclesContract

DoralRespiratory

GroupInhibited

VentralRespiratory

GroupActive

FORCEDRESPIRATION

Expiration

(3 seconds)

Anatomy and Physiology for EngineersSlide 11-18

Control of Respiration

Higher order centers alsocontrol pace and depthof respiration.

Indirectly via pons.Directly via stimulationof respiratory muscles.

Voluntary andinvoluntary control.

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Anatomy and Physiology for EngineersSlide 11-19

Review QuestionsDuring maximal exercise, hemoglobinreleases more O2 to active skeletal musclesthan at rest. Why ? Why would obstruction of the airways affectbody’s pH ? Explain physiology of “bends” ordecompression sickness. Describe a possible pulmonary treatment foran infant born prematurely (22-25 weeks).