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PowerPoint® Lecture Slides
prepared by
Betsy C. Brantley
Valencia College
CHAPTER
15
The Respiratory
System
© 2017 Pearson Education, Inc.
The Respiratory System (15-1)
• Consists of structures involved in:
• Physically moving air into and out of the lungs
• Gas exchange
• Takes place at air-filled pockets called alveoli
Five Functions of the Respiratory System (15-1)
1. Provides large area for gas exchange between air
and circulating blood
2. Moves air along respiratory passageways to and
from gas-exchange surfaces of the lungs
3. Protects respiratory surfaces from dehydration,
temperature changes, and pathogens
4. Produces sounds for speaking, singing, and other
forms of communication
5. Aids in sense of smell
Divisions of the Respiratory System (15-1)
• Can be divided based on anatomical structures
into:
• Upper respiratory system
• Includes nose, nasal cavity, paranasal sinuses, and
pharynx
• Structures filter, warm, and humidify incoming air
• Lower respiratory system
• Includes larynx, trachea, bronchi, and lungs
Figure 15-1 The Structures of the Respiratory System.
Upper Respiratory System
Nose
Nasal cavity
Tongue
Sinuses
Pharynx
Esophagus
Lower Respiratory System
Clavicle
Larynx
Trachea
Bronchus
Bronchioles
Smallest
bronchioles
Ribs
Right
lung
Left
lung
Alveoli
Diaphragm
Functional Zones of the Respiratory Tract (15-1)
• Respiratory tract refers to passageways carrying
air to and from exchange surfaces in lungs
• Divided into two portions
• Conducting portion
• From nasal cavity to larger bronchioles
• Filters, warms, and humidifies air
• Respiratory portion
• Small bronchioles and alveoli
• Where gas exchange occurs
Conducting Portion of the Respiratory
Tract (15-1)
• Epithelium lining passageway is respiratory
mucosa
• Ciliated columnar epithelium with many mucous cells
• Underlying lamina propria supports epithelium
• Mucus coats exposed surfaces of respiratory tract
• Cilia sweep mucus and trapped debris toward pharynx
• Process called the mucus, or mucocilary, escalator
• Debris and microorganisms swallowed and destroyed by
acids and enzymes in stomach
Figure 15-2 The Respiratory Mucosa.
Movement
of mucus
to pharynx
Ciliated columnar
epithelial cell
Mucous cell
Stem cell
Debris
Mucous
gland
Mucus layer
Lamina propria
a A diagrammatic view of the respiratory
epithelium of the trachea. The arrow
indicates the direction of mucus
transport inferior to the pharynx.
Superficial view
SEM × 1647
b A surface view of the epithelium. The cilia of
the epithelial cells form a dense layer that
resembles a shag carpet. The movement of
these cilia propels mucus across the
epithelial surface.
The Nose (15-2)
• Air enters through external nares, or nostrils
• Nostrils open into nasal cavity
• Nasal vestibule is space enclosed by flexible tissues
of nose
• Nasal septum divides cavity into right and left sides
• Hard palate forms floor of nasal cavity
• Soft palate extends behind hard palate and lies under
nasopharynx
• Nasal conchae project from lateral walls
• Help warm and humidify incoming air by increasing
turbulence of airflow
• Internal nares mark the border between nasal
cavity and nasopharynx
The Pharynx (15-2)
• Also called the throat
• Chamber shared by respiratory and digestive
systems
• Extends between internal nares and entrances to
larynx and esophagus
Three Subdivisions of the Pharynx (15-2)
1. Nasopharynx – from internal nares to posterior
edge of soft palate
• Lined by ciliated respiratory epithelium
• Contains pharyngeal tonsil and entrances to auditory
tubes
2. Oropharynx – from soft palate to base of tongue
• Lined by stratified squamous epithelium
• Contains the palatine tonsils
3. Laryngopharynx – from base of tongue at level
of hyoid bone to entrance of esophagus
• Lined by stratified squamous epithelium
Figure 15-3 The Nose, Nasal Cavity, and Pharynx.
Frontal sinus
Nasal Conchae
Nasal cavity
Superior
Middle
Internal nares
Inferior
Entrance to auditory tube
Nasal vestibule
Pharyngeal tonsil
Pharynx
External nares
Hard palate
Nasopharynx
Oral cavity
Oropharynx
Tongue
Laryngopharynx
Soft palate
Palatine tonsil
Mandible
Epiglottis
Lingual tonsil
Hyoid bone
Glottis
Thyroid cartilage
Cricoid cartilage
Trachea
Esophagus
Thyroid gland
The Larynx (15-2)
• Tube that surrounds and protects the glottis, or
“voice box”
• Air enters the larynx through narrow opening of the
glottis
• Larynx made of nine cartilages stabilized by
ligaments and skeletal muscles
• Three largest cartilages are: epiglottis, thyroid cartilage,
cricoid cartilage
• Three pairs of smaller cartilages include: arytenoid,
corniculate, cuneiform cartilages
Large Cartilages of the Larynx (15-2)
• Epiglottis
• Projects superior to glottis
• Covers glottis during swallowing
• Prevents entry of liquids and food into respiratory tract
• Thyroid cartilage
• Forms anterior and lateral surfaces of larynx
• Ridge on anterior surface is “Adam’s apple”
• Cricoid cartilage
• Ring of cartilage just inferior to thyroid cartilage
Figure 15-4a-b The Anatomy of the Larynx and Vocal Cords.
Epiglottis
Hyoid bone
Ligament of
false vocal cord
Extrinsic
(thyrohyoid)
ligament
Corniculate cartilage
Elastic ligament
of true vocal cord
Thyroid
cartilage
Larynx
Arytenoid cartilages
Ligament
Cricoid cartilage
Ligament
Tracheal cartilages
Trachea
a Anterior view.
b Posterior view.
Vocal Cord Structure (15-2)
• Two pairs of ligaments extending across the larynx
• False vocal cords are the upper pair of ligaments
• Inelastic
• Help prevent foreign objects from entering glottis
• Protect lower pair of ligaments
• True vocal cords are the lower pair of ligaments
• Elastic
• Connect thyroid and arytenoid cartilages
• Involved in sound production
• Glottis is made up of true vocal cords and space
between them
Figure 15-4c-e The Anatomy of the Larynx and Vocal Cords.
POSTERIOR
Corniculate cartilage
Glottis
(open)
Cuneiform cartilage
False vocal cord
Glottis
(closed)
Corniculate cartilage
Cuneiform cartilage
Glottis (open)
True vocal cord
False vocal cord
Epiglottis
True vocal cord
Root of tongue
Epiglottis
Root of tongue
ANTERIOR
c Glottis in the open position.
d Glottis in the closed position.
e This photograph is a representative
laryngoscopic view. For this view the
camera is positioned within the oropharynx, just superior to the larynx.
The Trachea (15-2)
• Tough, flexible tube
• Runs from cricoid cartilage to branches of primary
bronchi
• Walls supported by 15–20 C-shaped tracheal
cartilages
• Open parts of cartilages
• Face posteriorly, toward esophagus
• Allow passage of food along esophagus
• Are connected by elastic ligament and trachealis muscle
• Muscle under ANS control
• Sympathetic stimulation dilates trachea
Figure 15-5 The Anatomy of the Trachea.
Hyoid bone
Larynx
Esophagus
Tracheal ligament
Trachealis muscle
(smooth muscle)
Respiratory
epithelium
Trachea
Tracheal cartilage
Tracheal
cartilage
Mucous gland
Primary bronchi
Secondary bronchi
b A cross-sectional view of the trachea and esophagus
RIGHT LUNG
LEFT LUNG
a A diagrammatic anterior view showing the plane of section for part (b)
The Bronchi (15-2)
• Trachea branches into two bronchi:
• Right primary bronchus
• Supplies right lung
• Larger and at steeper angle
• Creates more likely pathway for foreign objects
• Left primary bronchus
• Supplies left lung
The Bronchial Tree (15-2)
• Formed by primary bronchi and their branches
• Secondary bronchi
• First branches off primary bronchi
• Enter lung lobes
• Two in left lung, three in right lung
• Tertiary bronchi
• Branch off secondary bronchi
• 9–10 in each lung
• Supply bronchopulmonary segment
Bronchioles (15-2)
• As proceed farther along bronchial tree:
• Diameter decreases
• Percentage of cartilage decreases
• Bronchiole
• Lung passageway when cartilage has disappeared
• Walls dominated by smooth muscle
• Sympathetic activation relaxes muscle, causing
bronchodilation
• Parasympathetic activation contracts muscle, causing
bronchoconstriction
Figure 15-6a The Bronchial Tree and a Lobule of the Lung.
Trachea
Cartilage plates
Left primary
bronchus
Visceral pleura
a The branching pattern of bronchi
and bronchioles in the left lung,
simplified
Secondary
bronchus
Tertiary bronchi
Smaller
bronchi
Bronchioles
Terminal
bronchiole
Alveoli in a
pulmonary
lobule
Respiratory
bronchiole
Bronchopulmonary
segment
Terminal to Respiratory Bronchioles (15-3)
• Terminal bronchioles are the finest conducting
passageways
• Average 0.3–0.5 mm in diameter
• Each supplies one pulmonary lobule
• Segment of lung tissue bound by connective tissue
partitions
• Supplied by a bronchiole, pulmonary arteriole, and venule
• Terminal bronchioles branch into respiratory
bronchioles
• May have some gas exchange ability
• Lead into alveolar ducts
Alveolar Ducts and Alveoli (15-3)
• Alveolar ducts end at alveolar sacs
• Chambers that connect to multiple individual alveoli
• Each lung contains about 150 million alveoli
• Give lung spongy, airy appearance
• Vastly increase surface area
• Total surface area of both lungs together is ~140 m2
• Allow for extensive, rapid gas diffusion to meet metabolic
needs
Figure 15-7a-b Alveolar Organization.
Alveoli
Respiratory bronchiole
Smooth muscle
Capillaries
Alveolar duct
Respiratory
bronchiole
Bands of
elastic fibers
Alveolar
sac
Alveolar
sac
Arteriole
Alveolus
a The basic structure of the distal end of a
single lobule. Note that multiple alveoli open
off a single alveolar duct, and that a network
of capillaries, supported by elastic fibers,
surrounds each alveolus.
Histology of the lung
b Low-power micrograph of lung tissue.
LM × 14
Structure of Alveoli (15-3)
• Primary cells are type I pneumocytes
• Unusually thin simple squamous epithelium
• Roaming alveolar macrophages
• Patrol epithelium, engulfing any particles
• Type II pneumocytes
• Produce surfactant
• Helps keep alveoli open by reducing surface tension
• Lack of surfactant triggers respiratory distress
syndrome
The Respiratory Membrane (15-3)
• Where diffusion of gases takes place
• Can be as thin as 0.1 µm
• Averages 0.5 µm
• Three layers
1. Alveolar epithelium – squamous epithelial cells lining
the alveoli
2. Capillary endothelium – of adjacent capillary
3. Fused basement membranes between alveolar and
endothelial cells
Figure 15-7c-d Alveolar Organization.
Type II
pneumocyte
Type I pneumocyte
Alveolar
macrophage
Red blood cell
Capillary lumen
Elastic fibers
Nucleus of
Capillary
endothelium endothelial cell
0.5 µm
Fused
Alveolar
basement epithelium
membrane
Alveolar macrophage
Surfactant
Alveolar air space
Capillary
d The respiratory membrane, which
Endothelial
cell of capillary
c A diagrammatic view of alveolar structure. A single capillary may be
involved in gas exchange with several alveoli simultaneously.
consists of an alveolar epithelial cell,
a capillary endothelial cell, and their
fused basement membranes.
The Lungs (15-3)
• Divided into lobes, separated by deep fissures
• Left lung has two lobes: superior and inferior
• Right lung has three lobes: superior, middle, and inferior
• Costal surface follows inner contours of rib cage
• Mediastinal surface of left lung has cardiac notch
• Provides space for pericardial cavity
Figure 15-8 The Gross Anatomy of the Lungs.
Apex
Superior lobe
Superior lobe
(costal surface)
Right lung
Left lung
Middle lobe
Cardiac notch (in
mediastinal surface)
Inferior lobe
Inferior lobe
Base
Anterior view
The Pleural Cavities (15-3)
• Surround each lung within thoracic cavity
• Pleura is serous membrane of pleural cavity
• Visceral pleura covers outer surface of lungs
• Parietal pleura lines inside of chest wall and diaphragm
• Pleural layers secrete pleural fluid, reducing friction
• Pleural cavity is potential space between the two layers
• Parietal and visceral layers usually in close contact
Figure 15-9 Anatomical Relationships in the Thoracic Cavity.
Parietal pleura
Mediastinum
Right pleural cavity
Visceral pleura
Right Lung
Left Lung
Pericardial cavity
Heart
Superior view
External and Internal Respiration (15-4)
• Respiration includes two integrated processes
1. External respiration
• Exchange of oxygen and carbon dioxide between body
fluids and external environment
2. Internal respiration
• Absorption of oxygen and release of carbon dioxide by
cells of the body
External Respiration (15-4)
• Includes three steps
1. Pulmonary ventilation, or breathing
• Physical movement of air into and out of lungs
2. Gas diffusion across respiratory membrane and
across capillary walls between blood and body tissues
3. Transport of O2 and CO2 in blood
Inadequate Oxygen Concentrations (15-4)
• Hypoxia
• Low tissue oxygen
• Metabolic activities become limited
• Anoxia
• Supply of oxygen cut off completely
• Cells die off quickly
• Damage from strokes or heart attacks are a result of
anoxia
Pulmonary Ventilation (15-5)
• The physical movement of air into and out of the
respiratory tract
• Primary function to maintain alveolar ventilation
• Movement of air into and out of alveoli
• Prevents buildup of carbon dioxide
• Ensures continuous supply of oxygen
Pressure and Airflow into Lungs (15-5)
• Air moves down pressure gradient
• In closed, flexible container (lung), air pressure is
altered by changing the volume of container
• Increase in volume decreases air pressure
• Decrease in volume increases air pressure
• Volume of lung depends on volume of thoracic
cavity
Changes in Thoracic Volumes (15-5)
• Diaphragm forms floor of thoracic cavity
• Relaxed diaphragm is dome-shaped
• Pushes up into thorax, compressing lungs
• Contraction pulls it downward, increasing volume of
thoracic cavity, expanding lungs
• Rib cage
• Elevation increases volume of thoracic cavity
• External intercostal muscles and accessory muscles
• Relaxation decreases volume of thoracic cavity
• Internal intercostals and other accessory muscles
Figure 15-10a Pulmonary Ventilation
Ribs and
sternum
elevate
Diaphragm
contracts
As the diaphragm is
depressed or the ribs
are elevated, the
volume of the thoracic
cavity increases and
air moves into the
lungs. The outward
movement of the ribs
as they are elevated
resembles the
outward swing of a
raised bucket handle.
Volume Change Causes Pressure
Gradient (15-5)
• Inhaling
• Increase in volume, pressure inside (Pi) decreases
• Pi lower than pressure outside (Po), air moves in
• Exhaling
• Decrease in volume, Pi increases
• Pi higher than Po, air moves out
• At end-inhalation and end-exhalation, Pi = Po
Figure 15-10b Pulmonary Ventilation
AT REST
Mediastinum
Pleural cavity
Right
lung
Left
lung
Diaphragm
Poutside = Pinside
When the rib cage and
diaphragm are at rest, the
pressures inside and outside
the lungs are equal, and no
air movement occurs.
Figure 15-10c Pulmonary Ventilation
INHALATION
Accessory Respiratory
Muscles
Sternocleidomastoid
muscle
Scalene muscles
Pectoralis minor muscle
Serratus anterior muscle
Primary Respiratory
Muscles
External intercostal
muscles
Diaphragm
Elevation of the rib cage
and contraction of the
diaphragm increase the
volume of the thoracic
cavity. Pressure within
the lungs decreases,
and air flows in.
Thoracic cavity volume increases
Poutside > Pinside
Figure 15-10d Pulmonary Ventilation
EXHALATION
Accessory Respiratory
Muscles
Transversus thoracis muscle
Internal intercostal muscles
Rectus abdominis
When the rib cage returns
to its original position and
the diaphragm relaxes, the
volume of the thoracic
cavity decreases. Pressure
Thoracic cavity volume decreases
within the lungs increases,
and air moves out.
Poutside < Pinside
Compliance (15-5)
• Compliance is ease with which lungs expand
• Greater compliance means easier to fill and empty lungs
• Lower compliance requires greater force to fill and
empty lungs
• Dramatically increases energy needed for breathing
• Compliance can be affected by these factors
• Loss of supporting tissues due to alveolar damage
increases compliance (as in emphysema)
• Decrease in surfactant decreases compliance (as in
respiratory distress syndrome)
• Limits on movements of thoracic cage (as with arthritis)
decreases compliance
Modes of Breathing (15-5)
• Quiet breathing
• Inhalation involves only primary muscles of inspiration:
diaphragm and external intercostals
• Diaphragm accounts for 75 percent of air movement
• Exhalation is passive
• Forced breathing
• Inhalation involves both primary and accessory muscles
• Exhalation uses internal intercostals and abdominals
Respiratory Cycle and Rate (15-5)
• Respiratory cycle
• A single breath of inhalation (inspiration) and exhalation
(expiration)
• Respiratory rate
• Number of breaths per minute
• Normal adult rate 12–18 breaths per minute
Lung Volumes and Capacities (15-5)
• Tidal volume (VT)
• Amount of air moved into or out of lungs in single
respiratory cycle during quiet breathing
• Expiratory reserve volume (ERV)
• Amount of air you can voluntarily expel at end of a
normal “exhale”, or quiet respiratory cycle
• Inspiratory reserve volume (IRV)
• Amount of air that can be taken in above tidal volume
• Vital capacity = VT + IRV + ERV
• Maximum amount of air that can be moved into and out
of lung in one respiratory cycle
Lung Volumes and Capacities cont. (15-5)
• Residual volume
• Amount of air remaining in lungs after maximal
exhalation
• Minimal volume
• Amount of air remaining in lungs after lung collapse
• Anatomic dead space
• Amount of air in conducting passageways
• Does not take part in gas exchange
• Averages about 150 mL (when tidal volume is 500 mL)
Figure 15-11 Pulmonary Volumes and Capacities.
Pulmonary Volumes and Capacities (adult male)
6000
Gender Differences
Inspiratory
reserve
volume (IRV)
Inspiratory
capacity
Volume (mL)
Tidal volume
(VT = 500 mL)
Males
2700
Total lung
capacity
Expiratory
reserve volume
(ERV)
Functional
residual
capacity
1200
0
Residual
volume
Time
1900
500
500
ERV 1000
700
Residual volume 1200
1100
VT
Total lung capacity 6000 mL
2200
Minimal volume
(30–120 mL)
IRV 3300
Vital
capacity
Vital
capacity
Females
4200 mL
Inspiratory
capacity
Functional
residual
capacity
Gas Exchange (15-6)
• Gas exchange depends on two factors
• Partial pressure gradient of gases involved
• Diffusion of molecules between gas and liquid
Partial Pressure of a Gas in a Mixture (15-6)
• 100 percent of atmospheric air is made up of:
• 78.6 percent nitrogen, 20.9 percent oxygen, 0.04 percent
carbon dioxide
• Remaining 0.5 percent is water vapor
• At sea level atmospheric pressure is 760 mm Hg
• Each gas in a mixture contributes a proportional
pressure, a partial pressure (Pgas)
• PO2 = 760 mm Hg × 20.9% = 159 mm Hg
Atmospheric vs. Alveolar Partial
Pressures (15-6)
• Air entering respiratory structures changes in
character
• Increase in water vapor and temperature
• Alveolar air is mixture of atmospheric air and residual
volume
• Exhaled air is changed also
• Mixes with air in conducting zone or dead space that
never reached alveoli
Partial Pressures in Pulmonary Circuit (15-6)
• Deoxygenated blood entering pulmonary arteries
• PO2 = 40 mm Hg; PCO2 = 45 mm Hg
• Alveolar air
• PO2 = 100 mm Hg; PCO2 = 40 mm Hg
• Gases move down partial pressure gradients
• Oxygen moves from alveolar air to capillaries
• Carbon dioxide moves from capillaries into alveolar air
• Blood entering pulmonary veins mixes with low
oxygen blood from capillaries around conducting
zone
• Blood entering left atrium has PO2 = 95 mm Hg
Figure 15-12a An Overview of Respiratory Processes and Partial Pressures in Respiration.
a External Respiration
PO2 = 40
PCO2 = 45
Alveolus
Respiratory
membrane
Pulmonary
circuit
Systemic
circuit
PO2 = 100
PCO2 = 40
Diffusion
Pulmonary
capillary
PO2 = 100
PCO2 = 40
Systemic
circuit
Partial Pressures in Systemic Circuit (15-6)
• Oxygenated blood entering systemic arteries
• PO2 = 95 mm Hg; PCO2 = 40 mm Hg
• Interstitial fluid
• PO2 = 40 mm Hg; PCO2 = 45 mm Hg
• Gases move down partial pressure gradients
• Oxygen moves from plasma to tissues
• Carbon dioxide moves from tissues to plasma
• Deoxygenated blood returning to right atrium
• PO2 = 40 mm Hg; PCO2 = 45 mm Hg
Figure 15-12b An Overview of Respiratory Processes and Partial Pressures in Respiration.
Systemic
circuit
Pulmonary
circuit
b Internal Respiration
Interstitial fluid
Systemic
circuit
PO2 = 95
PCO2 = 40
PO2 = 40
PCO2 = 45
Diffusion
PO2 = 40
PCO2 = 45
Systemic
capillary
Gas Transport in Blood (15-7)
• O2 and CO2 have limited ability to dissolve in plasma
• Tissues need more O2, and generate more CO2,
than can be dissolved
• Red blood cells (RBCs) can carry both gases on
hemoglobin
• CO2 can chemically convert to soluble compound
• As gases are removed from plasma, more diffuse in
• All reactions are temporary and completely
reversible
Oxygen Transport (15-7)
• 1.5 percent of O2 transported in solution in plasma
• Remainder binds to central iron in heme unit of
hemoglobin (Hb) molecule
• Reversible reaction
• Rate of release of O2 determined by:
• PO2 of tissues, pH, and temperature
• Low PO2, low pH, and high temp increases O2 release
Carbon Dioxide Transport (15-7)
• CO2 generated as product of aerobic cell
metabolism
• Transported in three ways
1. 7 percent of CO2 is dissolved in plasma
2. 23 percent is in RBC bound to Hb
• Bound to globin portion of Hb
• Forms carbaminohemoglobin
3. 70 percent is transported as bicarbonate ions
Carbon Dioxide Transport as Bicarbonate (15-7)
• Overall reaction is:
• This reaction occurs in RBCs
• Bicarbonate (HCO3–) diffuses out of RBC in
exchange for chloride ion (Cl–)
• Known as the chloride shift
• Reactions are rapid and reversed in pulmonary
capillaries
Figure 15-13 Carbon Dioxide Transport in Blood.
CO2 diffuses
into the
bloodstream
7% remains
dissolved in
plasma (as CO2)
93% diffuses
into RBCs
23% binds to Hb,
forming
carbaminohemoglobin,
Hb•CO2
RBC
H+ removed
by buffers,
especially Hb
PLASMA
70% converted to
H2CO3 (carbonic
acid) by the enzyme
carbonic anhydrase
H2CO3 dissociates
into H+ and HCO3–
H+
Cl–
HCO3– moves
out of RBC in
exchange for
CI– (chloride
shift)
Slide 4
Figure 15-14 A Summary of Gas Transport and Exchange.
O2 pickup
(PO2 = 100, PCO2 = 40)
O2 delivery
(PO2 = 95, PCO2 = 40)
Pulmonary
capillary
Plasma
Systemic
capillary
Red blood cell
Red blood cell
Cells in
peripheral
tissues
Alveolar
air space
Chloride
shift
Alveolar
air space
Pulmonary
capillary
CO2 delivery
(PO2 = 40, PCO2 = 45)
Cells in
peripheral
tissues
Systemic
capillary
CO2 pickup
(PO2 = 40, PCO2 = 45)
Maintaining O2 and CO2 Levels (15-8)
• Cells are continually absorbing oxygen and
generating carbon dioxide
• Rates of absorption and generation need to be
balanced with delivery and removal
• Two homeostatic processes maintain equilibrium
• Changes in blood flow and oxygen delivery under local
control
• Changes in depth and rate of respiration under control of
brain’s respiratory centers
Local Control of Respiration (15-8)
• In the tissues:
• Increased activity results in:
• Decrease in tissue PO2 and increase in PCO2
• Result is more rapid diffusion of O2 into cells, CO2 out of
cells
• In the lungs:
• When alveolar capillary PO2 is low:
• Precapillary sphincters constrict, shunting blood to high
PO2 pulmonary lobules
• When air in bronchioles has high PCO2 bronchioles dilate;
when low they constrict
• Causes airflow to be directed to lobules with high PCO2