1. No category

Chapter 22A
Respiratory System:
Slides by Barbara Heard and W. Rose.
figures from Marieb & Hoehn 9th ed.
Portions copyright Pearson Education
Respiratory System Functions
• Respiration
• Supply O2, dispose of CO2
• Four processes (next slide)
• Involves circulatory system
• Olfaction
• Speech
Processes of Respiration
• Pulmonary ventilation (breathing):
moving air into and out of 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 blood
vessels and tissues
© 2013 Pearson Education, Inc.
Respiratory
system
Circulatory
system
Respiratory System: Functional Anatomy
• Major organs
– Nose, nasal cavity, and paranasal sinuses
– Pharynx
– Larynx
– Trachea
– Bronchi and their branches
– Lungs and alveoli
© 2013 Pearson Education, Inc.
Figure 22.1 Major
respiratory organs
and surrounding
structures
Nasal cavity
Oral cavity
Nostril
Pharynx
Larynx
Trachea
Carina of
trachea
Right main
(primary)
bronchus
Right
lung
Left main
(primary)
bronchus
Left lung
Diaphragm
© 2013 Pearson Education, Inc.
Functional Anatomy
• 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
PLAY
Animation: Rotating face
© 2013 Pearson Education, Inc.
Nose
– Provides an airway for respiration
– Moistens and warms entering air
– Filters and cleans inspired air
– Serves as resonating chamber for speech
– Houses olfactory receptors
© 2013 Pearson Education, Inc.
Figure 22.2b The external nose.
Frontal bone
Nasal bone
Septal cartilage
Maxillary bone
(frontal process)
Nasal cartilages
Dense fibrous
connective tissue
Nares (nostrils)
External skeletal framework
© 2013 Pearson Education, Inc.
Nasal cavity
•
•
•
•
Divided by midline nasal septum
Opens into nasopharynx posteriorly
Roof: ethmoid and sphenoid bones
Lateral walls: ethmoid, inferior conchae, palatine
bones
• Floor: hard palate (maxilla & palatine bones),
soft palate (muscle)
• Lined with mucous membranes
– Olfactory mucosa
– Respiratory mucosa: ciliated; cilia sweep
mucus toward pharynx
© 2013 Pearson Education, Inc.
Frontal sinus
Superior, middle, and
inferior meatus
Superior
nasal concha Ethmoid
Middle
bone
nasal concha
Sphenoid
sinus
Nasal bone
Inferior nasal
concha
Maxillary bone
Palatine bone
Nasal cavity: left lateral wall
Nasal septum removed.
Copyright © 2010 Pearson Education, Inc.
Frontal
sinus
Nasal bone
Sphenoid
sinus
Perpendicular
plate of
ethmoid bone
Septal cartilage
Hard Palatine bone
palate Maxilla
Vomer
Nasal cavity: midline structures
Septum in place. Note ethmoid bone, vomer, septal cartilage.
Copyright © 2010 Pearson Education, Inc.
Figure 22.3b The upper respiratory tract.
Cribriform plate
of ethmoid bone
Sphenoid sinus
Frontal sinus
Nasal cavity
Nasal conchae
(superior, middle
and inferior)
Nasal meatuses
(superior, middle,
and inferior)
Nasal vestibule
Posterior nasal
aperture
Nasopharynx
Pharyngeal tonsil
Opening of
pharyngotympanic tube
Uvula
Nostril
Oropharynx
Palatine tonsil
Isthmus of the
fauces
Hard palate
Soft palate
Tongue
Lingual tonsil
Laryngopharynx
Esophagus
Larynx
Epiglottis
Vestibular fold
Thyroid cartilage
Vocal fold
Cricoid cartilage
Trachea
Thyroid gland
Illustration
© 2013 Pearson Education, Inc.
Hyoid bone
Figure 22.3a The upper respiratory tract.
Olfactory nerves
Olfactory
epithelium
Superior nasal concha
and superior nasal meatus
Mucosa
of pharynx
Middle nasal concha
and middle nasal meatus
Tubal
tonsil
Inferior nasal concha
and inferior nasal meatus
Pharyngotympanic
(auditory) tube
Nasopharynx
Hard palate
Soft palate
Uvula
Photograph
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
Functions of the Nasal Mucosa and
Conchae
• During inhalation: filter, heat, moisten air
• During exhalation: reclaim heat, moisture
© 2013 Pearson Education, Inc.
Paranasal Sinuses
• In frontal, sphenoid, ethmoid, and
maxillary bones
• Lighten skull; secrete mucus; help to warm
and moisten air
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
Upper respiratory tract
Pharynx
Nasopharynx
Oropharynx
Laryngopharynx
Regions of the pharynx
© 2013 Pearson Education, Inc.
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
• Pharyngotympanic (auditory) tubes drain
and equalize pressure in middle ear; open
into lateral walls
© 2013 Pearson Education, Inc.
Oropharynx
• Passageway for food and air from level of
soft palate to epiglottis
• Lining of stratified squamous epithelium
• Palatine tonsils-in lateral walls of fauces
• Lingual tonsil-on posterior surface of
tongue
© 2013 Pearson Education, Inc.
Laryngopharynx
• Passageway for food and air
• Posterior to upright epiglottis
• Extends to larynx, where continuous with
esophagus
• Lined with stratified squamous epithelium
© 2013 Pearson Education, Inc.
Figure 22.3b The upper respiratory tract.
Cribriform plate
of ethmoid bone
Sphenoid sinus
Frontal sinus
Nasal cavity
Nasal conchae
(superior, middle
and inferior)
Nasal meatuses
(superior, middle,
and inferior)
Nasal vestibule
Posterior nasal
aperture
Nasopharynx
Pharyngeal tonsil
Opening of
pharyngotympanic tube
Uvula
Nostril
Oropharynx
Palatine tonsil
Isthmus of the
fauces
Hard palate
Soft palate
Tongue
Lingual tonsil
Laryngopharynx
Esophagus
Larynx
Epiglottis
Vestibular fold
Thyroid cartilage
Vocal fold
Cricoid cartilage
Trachea
Thyroid gland
Illustration
© 2013 Pearson Education, Inc.
Hyoid bone
Larynx
• Structures through which air passes,
between laryngopharynx and trachea
• Provides patent airway
• Routes air and food into proper channels
• Voice production
© 2013 Pearson Education, Inc.
Larynx
• Thyroid cartilage (laryngeal prominence =
Adam's apple)
• Cricoid cartilage ring-shaped
• Other cartilages
• Epiglottis (elastic cartilage); covers laryngeal
inlet during swallowing to prevent food/water
from entering larynx
© 2013 Pearson Education, Inc.
Larynx
Epiglottis
Hyoid bone
Thyroid cartilage
Laryngeal prominence
(Adam’s apple)
Cricoid cartilage
Tracheal cartilages
Anterior superficial view
Larynx
Hyoid bone
Epiglottis
Vestibular fold
(false vocal cord)
Thyroid cartilage
Vocal fold
(true vocal cord)
Cricoid cartilage
Tracheal cartilages
Sagittal view; anterior surface to the right
© 2013 Pearson Education, Inc.
Larynx
• Vocal ligaments
– 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
• Vestibular folds (false vocal cords)
– Superior to vocal folds
– No part in sound production
– Help to close glottis during swallowing
© 2013 Pearson Education, Inc.
Figure 22.5. Vocal fold movements.
Base of tongue
Epiglottis
Vestibular fold
(false vocal cord)
Vocal fold (true
vocal cord)
Glottis
Lumen of
trachea
Vocal folds in
closed position;
closed glottis
© 2013 Pearson Education, Inc.
Vocal folds in
open position;
open glottis
Voice Production
• 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, lips
© 2013 Pearson Education, Inc.
Larynx
• Vocal folds can 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 stabilizes trunk during heavy lifting;
helps to empty bladder or bowel
© 2013 Pearson Education, Inc.
Trachea
• Air passageway from larynx into
mediastinum; “windpipe”
• Wall composed of three layers
– Mucosa-ciliated pseudostratified epithelium
with goblet cells
– Submucosa
– Adventitia-outermost layer made of connective
tissue; encases C-shaped rings of hyaline
cartilage
• Carina
– where trachea branches into two main bronchi
© 2013 Pearson Education, Inc.
Trachea
Posterior
Mucosa
Esophagus
Trachealis
muscle
Submucosa
Lumen of
trachea
Seromucous gland
in submucosa
Hyaline cartilage
Adventitia
Anterior
Cross section of trachea and esophagus
© 2013 Pearson Education, Inc.
Bronchi and Subdivisions
• Bronchial (respiratory) tree: Air
passages undergo ~23 orders of
branching
• Conducting zone
• Respiratory zone
© 2013 Pearson Education, Inc.
Conducting Zone Structures
• Trachea
• Right and left main bronchi
– Each main bronchus enters hilum of one lung
– Right main bronchus wider, shorter, more
vertical than left
• Lobar bronchi
– One to each lobe of each lung: 3 right, 2 left
• Segmental bronchi
• Smaller and smaller branches
– Bronchioles < 1 mm in diameter
– Terminal bronchioles < 0.5 mm diameter
© 2013 Pearson Education, Inc.
Figure 22.7 Conducting zone passages.
Trachea
Superior lobe
of left lung
Left main
(primary)
bronchus
Superior lobe
of right lung
Lobar (secondary)
bronchus
Segmental (tertiary)
bronchus
Middle lobe
of right lung
Inferior lobe
of right lung
© 2013 Pearson Education, Inc.
Inferior lobe
of left lung
Conducting Zone Structures
• From bronchi through bronchioles,
structural changes occur
– Cartilage rings gradually disappear
– Elastic fibers replace cartilage in bronchioles
– Epithelium changes from pseudostratified
columnar to cuboidal
– Cilia, goblet cells become sparse
– Relative amount of smooth muscle increases
• Allows constriction
© 2013 Pearson Education, Inc.
Respiratory Zone
•
•
•
•
•
Where gas exchange takes place
Begins at ends of 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
© 2013 Pearson Education, Inc.
Figure 22.8a Respiratory zone structures.
Alveoli
Alveolar duct
Respiratory bronchioles
Terminal
bronchiole
© 2013 Pearson Education, Inc.
Alveolar duct
Alveolar
sac
Figure 22.8b Respiratory zone structures.
Respiratory
bronchiole
Alveolar
duct
Alveoli
Alveolar
sac
© 2013 Pearson Education, Inc.
Alveolar
pores
Respiratory Membrane
• Alveolar and capillary walls and their fused
basement membranes
– ~0.5-µm-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
© 2013 Pearson Education, Inc.
Figure 22.9a Alveoli and the respiratory membrane.
Terminal bronchiole
Respiratory bronchiole
Smooth
muscle
Elastic
fibers
Alveolus
Capillaries
Diagrammatic view of capillary-alveoli relationships
© 2013 Pearson Education, Inc.
Alveoli
• Surrounded by fine elastic fibers and
pulmonary capillaries
• Alveolar pores connect adjacent alveoli
• Equalize air pressure throughout lung
• Alveolar macrophages keep alveolar
surfaces “clean”
– 2 million dead macrophages/hour carried by
cilia  throat  swallowed
© 2013 Pearson Education, Inc.
Figure 22.9c Alveoli and the respiratory membrane.
Red blood
cell
Nucleus of type I
alveolar cell
Alveolar pores
Capillary
Capillary
Macrophage
Endothelial cell
nucleus
Alveolus
Respiratory
membrane
Alveoli
(gas-filled
air spaces)
Red blood
cell in
capillary
Type II
alveolar
cell
Type I
alveolar
cell
Detailed anatomy of the respiratory membrane
© 2013 Pearson Education, Inc.
Alveolus
Alveolar
epithelium
Fused basement
membranes of
alveolar
epithelium and
capillary
endothelium
Capillary
endothelium
Lungs
• Composed primarily of alveoli
• Elastic connective tissue
• Apex (superior), base (rests on
diaphragm)
• Root (hilum): site of entry/exit of blood
vessels, bronchi, lymphatics, nerves
• Left lung smaller than right
– Cardiac notch-concavity for heart
– Superior, inferior lobes
• Right lung
– Superior, middle, inferior lobes
© 2013 Pearson Education, Inc.
Figure 22.10c Anatomical relationships of organs in the
thoracic cavity.
Vertebra
Right lung
Parietal pleura
Visceral pleura
Pleural cavity
Posterior
Esophagus
(in mediastinum)
Root of lung
at hilum
• Left main
bronchus
• Left pulmonary
artery
• Left pulmonary
vein
Left lung
Thoracic wall
Pulmonary trunk
Pericardial
membranes
Sternum
Heart (in mediastinum)
Anterior mediastinum
Anterior
Transverse section through the thorax, viewed from above. Lungs, pleural
membranes, and major organs in the mediastinum are shown.
© 2013 Pearson Education, Inc.
Figure 22.10a. Organs
in the thoracic cavity.
Intercostal
muscle
Rib
Lung
Parietal pleura
Pleural cavity
Visceral pleura
Trachea
Thymus
Apex of lung
Left
superior lobe
Right superior lobe
Horizontal fissure
Right middle lobe
Oblique fissure
Oblique
fissure
Left inferior
lobe
Right inferior lobe
Heart
(in mediastinum)
Diaphragm
Cardiac notch
Base of lung
Anterior view. The lungs flank mediastinal structures laterally.
© 2013 Pearson Education, Inc.
Figure 22.10b Anatomical relationships of organs in the thoracic cavity.
Apex of lung
Pulmonary
artery
Left
superior lobe
Oblique
fissure
Pulmonary
vein
Left inferior
lobe
Cardiac
impression
Hilum of lung
Oblique
fissure
Aortic
impression
© 2013 Pearson Education, Inc.
Left main
bronchus
Lobules
Photograph of medial view of the
left lung.
Figure 22.11 A cast of the bronchial tree.
Right lung
Right
superior
lobe (3
segments)
Left lung
Left superior
lobe
(4 segments)
Right
middle
lobe (2
segments)
Right
inferior lobe
(5 segments)
© 2013 Pearson Education, Inc.
Left inferior
lobe
(5 segments)
Pulmonary circulation
• Low pressure, low resistance
• Pulmonary arteries deliver systemic
venous blood to lungs for oxygenation
• Pulmonary veins carry oxygenated blood
from respiratory zones to heart
• Pulmonary capillary endothelium contains
angiotensin-converting enzyme
– Converts angiotensin I to angiotensin II.
(Renin converts angiotensinogen to Ang I.)
© 2013 Pearson Education, Inc.
Bronchial circulation
• Oxygenated blood for lung tissue
• Only circulatory pathway that goes from
systemic arteries to pulmonary veins
© 2013 Pearson Education, Inc.
Pleurae
• Thin, double-layered serosa
• Parietal pleura on thoracic wall, superior
face of diaphragm, around heart, between
lungs
• Visceral pleura on external lung surface
• Pleural fluid fills thin pleural cavity
– Provides lubrication and surface tension 
assists in expansion and recoil
© 2013 Pearson Education, Inc.
Figure 22.10c
Organs in the thoracic cavity
Vertebra
Right lung
Parietal pleura
Visceral pleura
Pleural cavity
Posterior
Esophagus
(in mediastinum)
Root of lung
at hilum
• Left main
bronchus
• Left pulmonary
artery
• Left pulmonary
vein
Left lung
Thoracic wall
Pulmonary trunk
Pericardial
membranes
Sternum
Heart (in mediastinum)
Anterior mediastinum
Anterior
Transverse section through the thorax, viewed from above. Lungs, pleural
membranes, and major organs in the mediastinum are shown.
© 2013 Pearson Education, Inc.
Mechanics of Breathing
• Pulmonary ventilation consists of two
phases
– Inspiration-gases flow into lungs
– Expiration-gases exit lungs
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
Intrapulmonary Pressure
• Intrapulmonary (intra-alveolar) pressure
(Ppul)
– Pressure in alveoli
– Fluctuates with breathing
– Always eventually equalizes with Patm
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
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
size
– One outward force tends to enlarge lungs
• Elasticity of chest wall pulls thorax outward
© 2013 Pearson Education, Inc.
Pressure Relationships
• If Pip = Ppul or Patm  lungs collapse
• (Ppul – Pip) = transpulmonary pressure
– Keeps airways open
– Greater transpulmonary pressure  larger
lungs
© 2013 Pearson Education, Inc.
Figure 22.12 Intrapulmonary and intrapleural pressure relationships.
Atmospheric pressure (Patm)
0 mm Hg (760 mm Hg)
Parietal pleura
Thoracic wall
Visceral pleura
Pleural cavity
Transpulmonary
pressure
4 mm Hg
(the difference
between 0 mm Hg
and −4 mm Hg)
–4
0
Lung
Diaphragm
© 2013 Pearson Education, Inc.
Intrapulmonary
pressure (Ppul)
0 mm Hg
(760 mm Hg)
Intrapleural
pressure (Pip)
−4 mm Hg
(756 mm Hg)
Homeostatic Imbalance
• 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
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
Forced Inspiration
• Vigorous exercise, COPD  accessory
muscles (scalenes, sternocleidomastoid,
pectoralis minor)  further increase in
thoracic cage size
© 2013 Pearson Education, Inc.
Figure 22.13 Changes in thoracic volume and sequence of events during inspiration and expiration. (1 of 2) Slide 1
Sequence of events
Changes in anterior-posterior and
superior-inferior dimensions
Changes in lateral dimensions
(superior view)
1 Inspiratory muscles
contract (diaphragm
descends; rib cage rises).
Inspiration
2 Thoracic cavity volume
increases.
3 Lungs are stretched;
intrapulmonary volume
increases.
Ribs are
elevated and
sternum
flares as
external
intercostals
contract.
External
intercostals
contract.
4 Intrapulmonary pressure
drops (to –1 mm Hg).
5 Air (gases) flows into
lungs down its pressure
gradient until intrapulmonary
pressure is 0 (equal to
atmospheric pressure).
© 2013 Pearson Education, Inc.
Diaphragm
moves inferiorly
during
contraction.
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
© 2013 Pearson Education, Inc.
Figure 22.13 Changes in thoracic volume and sequence of events during inspiration and expiration. (2 of 2) Slide 1
Sequence of events
Changes in anterior-posterior and
superior-inferior dimensions
Changes in lateral dimensions
(superior view)
1 Inspiratory muscles relax
(diaphragm rises; rib cage
descends due to recoil of
costal cartilages).
Expiration
2 Thoracic cavity volume
decreases.
3 Elastic lungs recoil
passively; intrapulmonary
Volume decreases.
Ribs and
sternum are
depressed
as external
intercostals
relax.
External
intercostals
relax.
4 Intrapulmonary pressure
rises (to +1 mm Hg).
5 Air (gases) flows out of
lungs down its pressure
gradient until intrapulmonary
pressure is 0.
© 2013 Pearson Education, Inc.
Diaphragm
moves
superiorly
as it relaxes.
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 of
air into and out of the lungs.
Volume (L)
Intrapulmonary pressure.
Pressure inside lung
decreases as lung volume
increases during
inspiration; pressure
increases during expiration.
Pressure relative to
atmospheric pressure (mm Hg)
Figure 22.14 Changes in intrapulmonary and intrapleural pressures during inspiration and expiration.
Inspiration
Expiration
Intrapulmonary
pressure
+2
0
–2
–4
Transpulmonary
pressure
–6
Intrapleural
pressure
–8
Volume of breath
0.5
0
5 seconds elapsed
© 2013 Pearson Education, Inc.
Physical Factors Influencing Pulmonary
Ventilation
• Three physical factors influence the ease
of air passage and the amount of energy
required for ventilation.
– Airway resistance
– Alveolar surface tension
– Lung compliance
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
Figure 22.15 Resistance in respiratory passageways.
Conducting
zone
Respiratory
zone
Resistance
Medium-sized
bronchi
Terminal
bronchioles
1
© 2013 Pearson Education, Inc.
5
10
15
Airway generation
(stage of branching)
20
23
Homeostatic Imbalance
• 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
© 2013 Pearson Education, Inc.
Alveolar Surface Tension
• Surface tension
– Attraction of liquid molecules for one another
at gas-liquid interface
– Resists any force that tends to increase
surface area of liquid
– Water has high surface tension
– Water layer on alveolar walls generates a
“shrinking” (closing) force
© 2013 Pearson Education, Inc.
Alveolar Surface Tension
• Surfactant
– Anything that reduces surface tension
– Type II alveolar cells make surfactant
(lipd/protein mix)
– Reduces surface tension of alveolar fluid and
discourages alveolar collapse
– Insufficient quantity in premature infants
causes infant respiratory distress
syndrome
© 2013 Pearson Education, Inc.
Lung Compliance
• Compliance = ΔV / ΔP
• ΔV = change in lung volume
• ΔP = change in transpulmonary pressure
Volume (mL)
2500
2000
1500
1000
500
0
© 2013 Pearson Education, Inc.
2
4
6
Pressure (mmHg)
8
Lung Compliance
• High lung compliance  easy to expand
lungs
• Normally high, due to
– Lung tissue that is easy to distend (stretch)
– Surfactant, which decreases alveolar surface
tension
• Diminished by
– Scar tissue (which is inelastic) replacing lung
tissue (fibrosis)
– Reduced production of surfactant
– Decreased flexibility of thoracic cage
© 2013 Pearson Education, Inc.
Lung Compliance
• Lung compliance is also influenced by
compliance of the thoracic wall, which
is decreased by:
– Deformities of thorax
– Ossification of costal cartilage
– Paralysis of intercostal muscles
© 2013 Pearson Education, Inc.