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The Respiratory System

• Major function-respiration– Supply body with O2 for cellular respiration;

dispose of CO2, a waste product of cellular respiration

– Its four processes involve both respiratory and circulatory systems

• Also functions in olfaction and speech

• Pulmonary ventilation (breathing)-movement of air into and outof lungs

• External respiration-O2 and CO2

exchange between lungs and blood

• Transport-O2 and CO2 in blood

• Internal respiration-O2 and CO2

exchange between systemic bloodvessels and tissues

Respiratorysystem

Circulatorysystem

Processes of Respiration

Respiratory System: Functional Anatomy

• Major organs– Nose, nasal cavity, and paranasal sinuses– Pharynx– Larynx– Trachea– Bronchi and their branches– Lungs and alveoli

Figure 22.1 The major respiratory organs in relation to surrounding structures.

Nasal cavity

Nostril

Larynx

Trachea

Carina of trachea

Right main (primary) bronchusRightlung

Oral cavity

Pharynx

Left main (primary) bronchus

Left lung

Diaphragm

• Respiratory zone-site of gas exchange – Microscopic structures-respiratory

bronchioles, alveolar ducts, and alveoli

• Conducting zone-conduits to gas exchange sites– Includes all other respiratory structures;

cleanses, warms, humidifies air

• Diaphragm and other respiratory muscles promote ventilation

Animation: Rotating face

Functional Anatomy

PLAYPLAY

The Nose

• Functions– Provides an airway for respiration– Moistens and warms entering air– Filters and cleans inspired air – Serves as resonating chamber for speech– Houses olfactory receptors

The Nose

• Two regions-external nose and nasal cavity

• External nose-root, bridge, dorsum nasi, and apex – Philtrum-shallow vertical groove inferior to

apex– Nostrils (nares)-bounded laterally by alae

Figure 22.2a The external nose.

Epicranius,frontal belly

Root andbridge of nose

Dorsum nasi

Ala of nose

Apex of nose

Naris (nostril)

Surface anatomy

Figure 22.2b The external nose.

Frontal bone

Nasal bone

Septal cartilage

Maxillary bone(frontal process)

Lateral process ofseptal cartilageMinor alarcartilagesDense fibrousconnective tissueMajor alarcartilages

External skeletal framework

The Nose

• Nasal cavity-within and posterior to external nose– Divided by midline nasal septum– Posterior nasal apertures (choanae) open

into nasal pharynx – Roof-ethmoid and sphenoid bones – Floor–hard (bone) and soft palates (muscle)

Nasal Cavity

• Nasal vestibule-nasal cavity superior to nostrils – Vibrissae (hairs) filter coarse particles from

inspired air

• Rest of nasal cavity lined with mucous membranes– Olfactory mucosa– Respiratory mucosa

Nasal Cavity

• Olfactory mucosa contains olfactory epithelium

• Respiratory mucosa– Pseudostratified ciliated columnar epithelium– Mucous and serous secretions contain

lysozyme and defensins – Cilia move contaminated mucus posteriorly to

throat– Inspired air warmed by plexuses of capillaries

and veins– Sensory nerve endings trigger sneezing

Figure 22.3b The upper respiratory tract.

Pharyngeal tonsil

Oropharynx

Cribriform plateof ethmoid bone

Sphenoid sinus

Posterior nasalaperture

Nasopharynx

Opening ofpharyngotympanic tube

Palatine tonsilIsthmus of thefauces

Laryngopharynx

Esophagus

Trachea

Frontal sinus

Nasal cavityNasal conchae(superior, middle and inferior)

Nasal meatuses(superior, middle,and inferior)Nasal vestibule

Nostril

Hard palate

Soft palate

Tongue

Lingual tonsil

Hyoid boneLarynxEpiglottisVestibular foldThyroid cartilageVocal foldCricoid cartilage

Thyroid gland

Illustration

Figure 22.3a The upper respiratory tract.

Olfactoryepithelium

Mucosa of pharynx

Tubaltonsil

Pharyngotympanic(auditory) tube

Nasopharynx

Olfactory nerves

Superior nasal concha and superior nasal meatus

Middle nasal concha and middle nasal meatus

Inferior nasal concha and inferior nasal meatus

Hard palate

Soft palate

Photograph

Nasal Cavity

• Nasal conchae-superior, middle, and inferior– Protrude medially from lateral walls– Increase mucosal area– Enhance air turbulence

• Nasal meatus– Groove inferior to each concha

Functions of the Nasal Mucosa and Conchae

• During inhalation, conchae and nasal mucosa– Filter, heat, and moisten air

• During exhalation these structures– Reclaim heat and moisture

Paranasal Sinuses

• In frontal, sphenoid, ethmoid, and maxillary bones

• Lighten skull; secrete mucus; help to warm and moisten air

Homeostatic Imbalance

• Rhinitis– Inflammation of nasal mucosa– Nasal mucosa continuous with mucosa of

respiratory tract spreads from nose throat chest

– Spreads to tear ducts and paranasal sinuses causing

• Blocked sinus passageways air absorbed vacuum sinus headache

Pharynx

• Muscular tube from base of skull to C6

– Connects nasal cavity and mouth to larynx and esophagus

– Composed of skeletal muscle

• Three regions– Nasopharynx– Oropharynx– Laryngopharynx

Figure 22.3c The upper respiratory tract.

Nasopharynx

Oropharynx

Laryngopharynx

Regions of the pharynx

Pharynx

Nasopharynx

• Air passageway posterior to nasal cavity• Lining - pseudostratified columnar

epithelium• Soft palate and uvula close nasopharynx

during swallowing• Pharyngeal tonsil (adenoids) on posterior

wall • Auditory tubes drain and equalize

pressure in middle ear; open into lateral walls

Oropharynx

• Passageway for food and air from level of soft palate to epiglottis

• Lining of stratified squamous epithelium

• Isthmus of fauces-opening to oral cavity

• Palatine tonsils-in lateral walls of fauces

• Lingual tonsil-on posterior surface of tongue

Laryngopharynx

• Passageway for food and air

• Posterior to upright epiglottis

• Extends to larynx, where continuous with esophagus

• Lined with stratified squamous epithelium

Figure 22.3b The upper respiratory tract.

Pharyngeal tonsil

Oropharynx

Cribriform plateof ethmoid bone

Sphenoid sinus

Posterior nasalaperture

Nasopharynx

Opening ofpharyngotympanic tube

Palatine tonsilIsthmus of thefauces

Laryngopharynx

Esophagus

Trachea

Frontal sinus

Nasal cavityNasal conchae(superior, middle and inferior)

Nasal meatuses(superior, middle,and inferior)Nasal vestibule

Nostril

Hard palate

Soft palate

Tongue

Lingual tonsil

Hyoid boneLarynxEpiglottisVestibular foldThyroid cartilageVocal foldCricoid cartilage

Thyroid gland

Illustration

Larynx

• Attaches to hyoid bone; opens into laryngopharynx; continuous with trachea

• Functions– Provides patent airway– Routes air and food into proper channels– Voice production

• Houses vocal folds

Larynx

• Nine cartilages of larynx– All hyaline cartilage except epiglottis– Thyroid cartilage with laryngeal

prominence (Adam's apple)– Ring-shaped cricoid cartilage– Paired arytenoid, cuneiform, and

corniculate cartilages– Epiglottis-elastic cartilage; covers laryngeal

inlet during swallowing; covered in taste bud-containing mucosa

Figure 22.4a The larynx.

Body of hyoid bone

Thyroid cartilage

Laryngeal prominence(Adam’s apple)

Cricothyroid ligament

Cricotracheal ligament

Epiglottis

Thyrohyoidmembrane

Cricoid cartilage

Tracheal cartilages

Anterior superficial view

Figure 22.4b The larynx.

Epiglottis

Thyrohyoidmembrane

Cuneiform cartilage

Corniculate cartilage

Arytenoid cartilage

Arytenoid muscles

Cricoid cartilage

Tracheal cartilages

Body of hyoid bone

Thyrohyoid membrane

Fatty pad

Vestibular fold(false vocal cord)

Thyroid cartilage

Vocal fold(true vocal cord)

Cricothyroid ligament

Cricotracheal ligament

Sagittal view; anterior surface to the right

Figure 22.4c The larynx.

Epiglottis

Hyoid bone

Thyroidcartilage

Lateralthyrohyoidmembrane

Corniculatecartilage

Arytenoidcartilage

Glottis

Cricoidcartilage

Trachealcartilages

Photograph of cartilaginous frameworkof the larynx, posterior view

Figure 22.4d The larynx.

Posterior cricoarytenoid muscle on cricoidcartilage

Trachea

Corniculatecartilage

Laryngealinlet

Epiglottis

Photograph of posterior aspect(d)

Larynx

• Vocal ligaments-deep to laryngeal mucosa– Attach arytenoid cartilages to thyroid cartilage– Contain elastic fibers – Form core of vocal folds (true vocal cords)

• Glottis-opening between vocal folds• Folds vibrate to produce sound as air rushes up

from lungs

Larynx

• Vestibular folds (false vocal cords)– Superior to vocal folds– No part in sound production– Help to close glottis during swallowing

Figure 22.5 Movements of the vocal folds.

Vestibular fold (false vocal cord)

Base of tongue

Epiglottis

Vocal fold (true vocal cord)

Glottis

Inner lining of trachea

Cuneiform cartilage

Corniculate cartilage

Vocal folds in closed position; closed glottis Vocal folds in open position; open glottis

Epithelium of Larynx

• Superior portion–stratified squamous epithelium

• Inferior to vocal folds–pseudostratified ciliated columnar epithelium

Voice Production

• Speech-intermittent release of expired air while opening and closing glottis

• Pitch determined by length and tension of vocal cords

• Loudness depends upon force of air• Chambers of pharynx, oral, nasal, and sinus

cavities amplify and enhance sound quality • Sound is "shaped" into language by muscles of

pharynx, tongue, soft palate, and lips

Larynx

• Vocal folds may act as sphincter to prevent air passage

• Example-Valsalva's maneuver– Glottis closes to prevent exhalation– Abdominal muscles contract– Intra-abdominal pressure rises – Helps to empty rectum or stabilizes trunk

during heavy lifting

Trachea

• Windpipe–from larynx into mediastinum

• Wall composed of three layers– Mucosa-ciliated pseudostratified epithelium

with goblet cells – Submucosa-connective tissue with

seromucous glands– Adventitia-outermost layer made of

connective tissue; encases C-shaped rings of hyaline cartilage

Trachea

• Trachealis muscle– Connects posterior parts of cartilage rings– Contracts during coughing to expel mucus

• Carina– Spar of cartilage on last, expanded tracheal

cartilage– Point where trachea branches into two main

bronchi

Figure 22.6a Tissue composition of the tracheal wall.

Esophagus

Trachealismuscle

Lumen oftrachea

Posterior

Mucosa

Submucosa

Hyaline cartilage

Adventitia

Seromucous glandin submucosa

Figure 22.6b Tissue composition of the tracheal wall.

Goblet cell

• Pseudostratified ciliated columnar epithelium

• Lamina propria (connective tissue)

Mucosa

Submucosa

Hyaline cartilage

Seromucous glandIn submucosa

Photomicrograph of the trachealwall (320x)

Figure 22.6c Tissue composition of the tracheal wall.

Scanning electron micrograph of cilia in thetrachea (2500x)

Bronchi and Subdivisions

• Air passages undergo 23 orders of branching bronchial (respiratory) tree

• From tips of bronchial tree conducting zone structures respiratory zone structures

Conducting Zone Structures

• Trachea right and left main (primary) bronchi

• Each main bronchus enters hilum of one lung– Right main bronchus wider, shorter, more

vertical than left

• Each main bronchus branches into lobar (secondary) bronchi (three on right, two on left)– Each lobar bronchus supplies one lobe

• Each lobar bronchus branches into segmental (tertiary) bronchi– Segmental bronchi divide repeatedly

• Branches become smaller and smaller – Bronchioles-less than 1 mm in diameter– Terminal bronchioles-smallest-less than

0.5 mm diameter

Figure 22.7 Conducting zone passages.

Superior lobe of right lung

Middle lobeof right lung

Inferior lobeof right lung

Trachea

Superior lobeof left lung

Left main(primary)bronchus

Lobar (secondary)bronchus

Segmental (tertiary)bronchus

Inferior lobeof left lung

• From bronchi through bronchioles, structural changes occur– Cartilage rings become irregular plates; in

bronchioles elastic fibers replace cartilage– Epithelium changes from pseudostratified

columnar to cuboidal; cilia and goblet cells become sparse

– Relative amount of smooth muscle increases• Allows constriction

Respiratory Zone

• Begins as terminal bronchioles respiratory bronchioles alveolar ducts alveolar sacs – Alveolar sacs contain clusters of alveoli

• ~300 million alveoli make up most of lung volume• Sites of gas exchange

Figure 22.8a Respiratory zone structures.

Alveolar duct

Respiratory bronchioles

Terminalbronchiole

Alveoli

Alveolar duct

Alveolar sac

Figure 22.8b Respiratory zone structures.

Respiratorybronchiole

Alveolarduct

Alveoli

Alveolarsac

Alveolarpores

Respiratory Membrane

• Alveolar and capillary walls and their fused basement membranes– ~0.5- m-thick; gas exchange across

membrane by simple diffusion

• Alveolar walls– Single layer of squamous epithelium (type I

alveolar cells)

• Scattered cuboidal type II alveolar cells secrete surfactant and antimicrobial proteins

Figure 22.9a Alveoli and the respiratory membrane.

Terminal bronchiole

Respiratory bronchiole

Smoothmuscle

Elasticfibers

Alveolus

Capillaries

Diagrammatic view of capillary-alveoli relationships

Figure 22.9b Alveoli and the respiratory membrane.

Scanning electron micrograph of pulmonary capillary casts (70x)

Alveoli

• Surrounded by fine elastic fibers and pulmonary capillaries

• Alveolar pores connect adjacent alveoli• Equalize air pressure throughout lung

• Alveolar macrophages keep alveolar surfaces sterile– 2 million dead macrophages/hour carried by

cilia throat swallowed

Figure 22.9c Alveoli and the respiratory membrane.

Red bloodcell incapillary

Alveoli(gas-filledair spaces)

Type IIalveolarcell

Type Ialveolarcell

Capillary

MacrophageEndothelial cellnucleus

Respiratorymembrane

AlveolarepitheliumFused basementmembranes ofalveolarepithelium andcapillaryendotheliumCapillaryendothelium

Capillary

Alveolus

Nucleus of type Ialveolar cell

Alveolar pores

Red bloodcell

Alveolus

Detailed anatomy of the respiratory membrane

• Occupy all thoracic cavity except mediastinum

• Root-site of vascular and bronchial attachment to mediastinum

• Costal surface-anterior, lateral, and posterior surfaces

• Composed primarily of alveoli

• Balance–stroma-elastic connective tissue elasticity

Figure 22.10c Anatomical relationships of organs in the thoracic cavity.

Transverse section through the thorax, viewed from above. Lungs, pleuralmembranes, and major organs in the mediastinum are shown.

Posterior

Parietal pleura

Visceral pleura

Pleural cavity

Pericardial membranes

Sternum

Vertebra

Esophagus(in mediastinum)

Root of lungat hilum• Left mainbronchus• Left pulmonaryartery• Left pulmonaryvein

Thoracic wall

Heart (in mediastinum)Anterior mediastinum

Pulmonary trunk

Right lung

• Apex-superior tip; deep to clavicle• Base-inferior surface; rests on diaphragm• Hilum-on mediastinal surface; site for

entry/exit of blood vessels, bronchi, lymphatic vessels, and nerves

• Left lung smaller than right– Cardiac notch-concavity for heart– Separated into superior and inferior lobes by

oblique fissure

• Right lung– Superior, middle, inferior lobes separated by

oblique and horizontal fissures

• Bronchopulmonary segments (10 right, 8–10 left) separated by connective tissue septa– If diseased can be individually removed

• Lobules-smallest subdivisions visible to naked eye; served by bronchioles and their branches

Figure 22.10a Anatomical relationships of organs in the thoracic cavity.

TracheaThymus

Apex of lung

Right inferior lobe

Horizontal fissure

Right superior lobe

Oblique fissure

Right middle lobe

Heart(in mediastinum)

Diaphragm

Base of lung

Intercostal muscleRib

Parietal pleuraPleural cavityVisceral pleura

Leftsuperior lobe

Obliquefissure

Left inferiorlobe

Cardiac notch

Anterior view. The lungs flank mediastinal structures laterally.

Figure 22.10b Anatomical relationships of organs in the thoracic cavity.

Apex of lung

Pulmonary artery

Left mainbronchus

Pulmonaryvein

Cardiacimpression

Obliquefissure

Lobules

Photograph of medial view of theleft lung.

Leftsuperior lobe

Obliquefissure

Left inferiorlobe

Hilum of lung

Aorticimpression

Figure 22.11 A cast of the bronchial tree.

Right lung Left lung

Left superiorlobe(4 segments)

Left inferiorlobe(5 segments)

Rightinferior lobe(5 segments)

Rightmiddlelobe (2segments)

Rightsuperiorlobe (3segments)

Blood Supply

• Pulmonary circulation (low pressure, high volume)– Pulmonary arteries deliver systemic venous

blood to lungs for oxygenation• Branch profusely; feed into pulmonary capillary

networks

– Pulmonary veins carry oxygenated blood from respiratory zones to heart

Blood Supply

– Lung capillary endothelium contains enzymes that act on substances in blood

• E.g., angiotensin-converting enzyme–activates blood pressure hormone

Blood Supply

• Bronchial arteries provide oxygenated blood to lung tissue– Arise from aorta and enter lungs at hilum– Part of systemic circulation (high pressure,

low volume) – Supply all lung tissue except alveoli– Bronchial veins anastomose with pulmonary

veins• Pulmonary veins carry most venous blood back to

Pleurae

• Thin, double-layered serosa; divides thoracic cavity into two pleural compartments and mediastinum

• Parietal pleura on thoracic wall, superior face of diaphragm, around heart, between lungs

• Visceral pleura on external lung surface• Pleural fluid fills slitlike pleural cavity

– Provides lubrication and surface tension assists in expansion and recoil

Figure 22.10c Anatomical relationships of organs in the thoracic cavity.

Transverse section through the thorax, viewed from above. Lungs, pleuralmembranes, and major organs in the mediastinum are shown.

Posterior

Parietal pleura

Visceral pleura

Pleural cavity

Pericardial membranes

Sternum

Vertebra

Esophagus(in mediastinum)

Root of lungat hilum• Left mainbronchus• Left pulmonaryartery• Left pulmonaryvein

Thoracic wall

Heart (in mediastinum)Anterior mediastinum

Pulmonary trunk

Right lung

Mechanics of Breathing

• Pulmonary ventilation consists of two phases– Inspiration-gases flow into lungs– Expiration-gases exit lungs

Pressure Relationships in the Thoracic Cavity

• Atmospheric pressure (Patm)

– Pressure exerted by air surrounding body – 760 mm Hg at sea level = 1 atmosphere

• Respiratory pressures described relative to Patm

– Negative respiratory pressure-less than Patm

– Positive respiratory pressure-greater than Patm

– Zero respiratory pressure = Patm

Intrapulmonary Pressure

• Intrapulmonary (intra-alveolar) pressure (Ppul)

– Pressure in alveoli– Fluctuates with breathing

– Always eventually equalizes with Patm

Intrapleural Pressure

• Intrapleural pressure (Pip)

– Pressure in pleural cavity– Fluctuates with breathing

– Always a negative pressure (<Patm and <Ppul)

– Fluid level must be minimal• Pumped out by lymphatics

• If accumulates positive Pip pressure lung collapse

Intrapleural Pressure

• Negative Pip caused by opposing forces

– Two inward forces promote lung collapse• Elastic recoil of lungs decreases lung size• Surface tension of alveolar fluid reduces alveolar

– One outward force tends to enlarge lungs• Elasticity of chest wall pulls thorax outward

Pressure Relationships

• If Pip = Ppul or Patm lungs collapse

• (Ppul – Pip) = transpulmonary pressure

– Keeps airways open– Greater transpulmonary pressure larger

Figure 22.12 Intrapulmonary and intrapleural pressure relationships.

Atmospheric pressure (Patm)0 mm Hg (760 mm Hg)

Thoracic wall

Parietal pleura

Visceral pleura

Pleural cavity

Transpulmonarypressure4 mm Hg(the differencebetween 0 mm Hgand −4 mm Hg)

Intrapleuralpressure (Pip)−4 mm Hg(756 mm Hg)

Intrapulmonarypressure (Ppul)0 mm Hg(760 mm Hg)

Diaphragm

• Atelectasis (lung collapse) due to– Plugged bronchioles collapse of alveoli– Pneumothorax-air in pleural cavity

• From either wound in parietal or rupture of visceral pleura

• Treated by removing air with chest tubes; pleurae heal lung reinflates

Pulmonary Ventilation

• Inspiration and expiration

• Mechanical processes that depend on volume changes in thoracic cavity– Volume changes pressure changes– Pressure changes gases flow to equalize

pressure

Boyle's Law

• Relationship between pressure and volume of a gas– Gases fill container; if container size reduced

increased pressure

• Pressure (P) varies inversely with volume (V): – P1V1 = P2V2

Inspiration

• Active process– Inspiratory muscles (diaphragm and external

intercostals) contract – Thoracic volume increases intrapulmonary

pressure drops (to 1 mm Hg)– Lungs stretched and intrapulmonary volume

increases– Air flows into lungs, down its pressure

gradient, until Ppul = Patm

Forced Inspiration

• Vigorous exercise, COPD accessory muscles (scalenes, sternocleidomastoid, pectoralis minor) further increase in thoracic cage size

Figure 22.13 Changes in thoracic volume and sequence of events during inspiration and expiration. (1 of 2) Slide 1

Inspiratory musclescontract (diaphragmdescends; rib cage rises).

Thoracic cavity volumeincreases.

Lungs are stretched;intrapulmonary volumeincreases.

Intrapulmonary pressuredrops (to –1 mm Hg).

Air (gases) flows intolungs down its pressuregradient until intrapulmonarypressure is 0 (equal toatmospheric pressure).

Sequence of events Changes in anterior-posterior andsuperior-inferior dimensions

Changes in lateral dimensions(superior view)

5Diaphragmmoves inferiorlyduringcontraction.

Ribs areelevated and sternumflares asexternalintercostalscontract.

Externalintercostalscontract.

Diaphragmmoves inferiorlyduringcontraction.

Externalintercostalscontract.Intrapulmonary pressure

drops (to –1 mm Hg).

Intrapulmonary pressuredrops (to –1 mm Hg).

Air (gases) flows intolungs down its pressuregradient until intrapulmonarypressure is 0 (equal toatmospheric pressure).

5Diaphragmmoves inferiorlyduringcontraction.

Expiration

• Quiet expiration normally passive process– Inspiratory muscles relax – Thoracic cavity volume decreases– Elastic lungs recoil and intrapulmonary

volume decreases pressure increases (Ppul rises to +1 mm Hg)

– Air flows out of lungs down its pressure gradient until Ppul = 0

• Note: forced expiration-active process; uses abdominal (oblique and transverse) and internal intercostal muscles

5 Diaphragmmovessuperiorlyas it relaxes.

Ribs andsternum aredepressedas externalintercostalsrelax.

Externalintercostalsrelax.

Inspiratory muscles relax(diaphragm rises; rib cagedescends due to recoil ofcostal cartilages).

Thoracic cavity volumedecreases.

Elastic lungs recoilpassively; intrapulmonaryVolume decreases.

Intrapulmonary pressurerises (to +1 mm Hg).

Air (gases) flows out oflungs down its pressuregradient until intrapulmonarypressure is 0.

Diaphragmmovessuperiorlyas it relaxes.

5 Diaphragmmovessuperiorlyas it relaxes.

Air (gases) flows out oflungs down its pressuregradient until intrapulmonarypressure is 0.

Figure 22.14 Changes in intrapulmonary and intrapleural pressures during inspiration and expiration.

Intrapulmonary pressure. Pressure inside lungdecreases as lung volume increases duringinspiration; pressureincreases during expiration.

Intrapleural pressure.Pleural cavity pressure becomes more negative as chest wall expands during inspiration. Returns to initial value as chest wall recoils.

Volume of breath. During each breath, the pressure gradients move 0.5 liter ofair into and out of the lungs.

tive t

Inspiration Expiration

Intrapulmonarypressure

Trans-pulmonarypressure

Intrapleuralpressure

Volume of breath

5 seconds elapsed

Physical Factors Influencing Pulmonary Ventilation

• Three factors hinder air passage and pulmonary ventilation; require energy to overcome– Airway resistance– Alveolar surface tension– Lung compliance

Airway Resistance

• Friction-major nonelastic source of resistance to gas flow; occurs in airways

• Relationship between flow (F), pressure (P), and resistance (R) is:

– ∆P - pressure gradient between atmosphere and alveoli (2 mm Hg or less during normal quiet breathing)

– Gas flow changes inversely with resistance

Airway Resistance

• Resistance usually insignificant– Large airway diameters in first part of

conducting zone– Progressive branching of airways as get

smaller, increasing total cross-sectional area– Resistance greatest in medium-sized bronchi

• Resistance disappears at terminal bronchioles where diffusion drives gas movement

Conductingzone

Respiratoryzone

Medium-sizedbronchi

Terminalbronchioles

1 5 10 15 20 23Airway generation

(stage of branching)

Figure 22.15 Resistance in respiratory passageways.

• As airway resistance rises, breathing movements become more strenuous

• Severe constriction or obstruction of bronchioles– Can prevent life-sustaining ventilation– Can occur during acute asthma attacks; stops

ventilation

• Epinephrine dilates bronchioles, reduces air resistance

Alveolar Surface Tension

• Surface tension– Attracts liquid molecules to one another at

gas-liquid interface – Resists any force that tends to increase

surface area of liquid– Water–high surface tension; coats alveolar

walls reduces them to smallest size

Alveolar Surface Tension

• Surfactant– Detergent-like lipid and protein complex

produced by type II alveolar cells– Reduces surface tension of alveolar fluid and

discourages alveolar collapse– Insufficient quantity in premature infants

causes infant respiratory distress syndrome alveoli collapse after each breath

Lung Compliance

• Measure of change in lung volume that occurs with given change in transpulmonary pressure

• Higher lung compliance easier to expand lungs

• Normally high due to– Distensibility of lung tissue – Alveolar surface tension

Lung Compliance

• Diminished by– Nonelastic scar tissue replacing lung tissue

(fibrosis) – Reduced production of surfactant– Decreased flexibility of thoracic cage

Lung Compliance

• Homeostatic imbalances that reduce compliance – Deformities of thorax– Ossification of costal cartilage– Paralysis of intercostal muscles

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