Chapter 17
Mechanics of
Breathing
About this Chapter
• The respiratory system
• Gas laws
• Ventilation
Respiratory System
Functions
• External Respiration
• Exchange of gases between the atmosphere
and the blood
• Homeostatic regulation of body pH
• Protection from inhaled pathogens and
irritating substances
• Vocalization
Respiratory System
Principles of Bulk Flow
• Flow from regions of higher to lower pressure
• Muscular pump creates pressure gradients
• Resistance to flow
• Diameter of tubes
Respiratory System
CO2
• Overview of
external and
cellular
respiration
O2
Exchange I:
atmosphere
to lung
(ventilation)
Airways
Alveoli
of lungs
CO2 O2
Exchange II:
lung to blood
O2
CO2
Pulmonary
circulation
Transport of
gases in
the blood
Systemic
circulation
CO2
O2
CO2
Exchange III:
blood to cells
O2
Cellular
respiration
Cells
Nutrients
ATP
Figure 17-1
Respiratory System Components
• Conducting system
• Alveoli
• Bones and muscle of thorax
Respiratory System
ANATOMY SUMMARY
THE LUNGS AND THORACIC CAVITY
Pharynx
Nasal cavity
Vocal cords
Tongue
Esophagus
Upper
respiratory
system
Larynx
Trachea
Lower
respiratory
system
Right lung
Right
bronchus
Left lung
Diaphragm
Left bronchus
(a) The respiratory system
Figure 17-2a
Muscles Used for Ventilation
Sternocleidomastoids
Scalenes
Internal
intercostals
External
intercostals
Diaphragm
Abdominal
muscles
Muscles of
inspiration
Muscles of
expiration
(b) Muscles used for ventilation
Figure 17-2b
The Respiratory System
Air-filled
balloon
Fluid-filled balloon
Air space
of lung
Pleural
fluid
Pleural
membrane
Figure 17-3
Branching of Airways
ANATOMY SUMMARY
THE LUNGS AND THORACIC CAVITY
Larynx
Trachea
Cartilage
ring
Left primary
bronchus
Secondary
bronchus
Bronchiole
Alveoli
(e) Branching of airways
Figure 17-2e
Branching of the Airways
Figure 17-4
Conditioning Air
• Warming air to body temperature
• Adding water vapor
• Filtering out foreign material
Ciliated Respiratory Epithelium
Cilia move mucus to pharynx
Dust particle
Mucus layer traps
inhaled particles.
Watery saline layer
allows cilia to
push mucus
toward pharynx.
Cilia
Goblet cell
secretes mucus.
Nucleus of
columnar
epithelial cell
Basement
membrane
Ciliated epithelium of the trachea
Figure 17-5
Alveolar Structure – Note cell types of alveoli
Figure 17-2g
Pulmonary Circulation
• Right ventricle  pulmonary trunk  lungs 
pulmonary veins  left atrium
• Note oxygenation
Anatomy Review
PLAY
Interactive Physiology® Animation: Respiratory
System: Anatomy Review
Gas Laws
Table 17-1
Gas Laws
• Pgas = Patm  % of gas in atmosphere
Table 17-2
Boyle’s Law
• Gases move from areas of high pressure to
areas of low pressure
Figure 17-6
Spirometer
Bell
Inspiration Expiration
Inspiration Expiration
Air
0.5
Volume
(L)
Water
0
Time
Figure 17-7
Lung Volumes and Capacities
Figure 17-8
Air Flow
• Flow  P/R
• Alveolar pressure or intrapleural pressure can
be measured
• Single respiratory cycle consists of one
inspiration followed by one expiration
Movement of the Diaphragm
Figure 17-9a
Movement of the Diaphragm
Figure 17-9b
Movement of the Diaphragm
Figure 17-9c
Dimensions of the Thoracic Cavity During
Inspiration
Figure 17-10a
Dimensions of the Thoracic Cavity During
Inspiration
Figure 17-10b
Pressure Changes During Quiet Breathing
Inspiration
Expiration
Inspiration
Expiration
+2
Alveolar
pressure
(mm Hg)
Trachea
A1
A4
A3
+1
0
A5
Bronchi
–1
A2
–2
Lung
B1
Intrapleural
pressure
(mm Hg)
B3
–3
–4
–5
Diaphragm
Right pleural
cavity
–6
B2
Left pleural
cavity
750
Volume
of air
moved
(mL)
500
C2
250
C1
C3
0
1
2
3
4
5
Time (sec)
6
7
8
Figure 17-11
Subatmospheric Pressure in the Pleural Cavity
P = –3 mm Hg
Intrapleural pressure
is subatmospheric.
Ribs
Intrapleural
space
Pleural
membranes
Diaphragm
Elastic recoil of the Elastic recoil of lung
chest wall tries to pull creates an inward pull.
the chest wall outward.
(a) Normal lung at rest
Figure 17-12a
Subatmospheric Pressure in the Pleural Cavity
• Pneumothorax results in collapsed lung that
cannot function normally
P = Patm
Knife
Lung collapses to
unstretched size
Intrapleural
space
Pleural
membranes
The rib cage
expands slightly.
If the sealed pleural cavity is opened
to the atmosphere, air flows in.
(b) Pneumothorax
Figure 17-12b
Compliance and Elastance
• Compliance: ability to stretch
• High compliance
• Stretches easily
• Low compliance
• Requires more force
• Restrictive lung diseases
• Fibrotic lung diseases
• Inadequate surfactant production
• Elastance: returning to its resting volume
when stretching force is released
Law of LaPlace
• Surface tension is created by the thin fluid
layer between alveolar cells and the air
Figure 17-13
Surfactant
• More concentrated in smaller alveoli
• Mixture containing proteins and
phospholipids
• Newborn respiratory distress syndrome
• Premature babies
• Inadequate surfactant concentrations
Air Flow
Table 17-3
Pulmonary Ventilation
PLAY
Interactive Physiology® Animation: Respiratory
System: Pulmonary Ventilation
Ventilation
• Total pulmonary ventilation is greater than
alveolar ventilation because of dead space
• Total pulmonary ventilation = ventilation rate
 tidal volume
Ventilation
Dead space filled
with fresh air
150
mL
1
2700 mL
The first exhaled
air comes out of
the dead space.
Only 350 mL
leaves the alveoli.
2 Exhale 500 mL
(tidal volume)
Atmospheric
air
Dead space is
filled with
fresh air.
Only 350 mL
of fresh air
reaches alveoli
The first 150 mL
of air into the
alveoli is stale
air from the
dead space.
1 End of inspiration
3
At the end of expiration, the
dead space is filled with
“stale” air from alveoli.
4
Inhale 500 mL
of fresh air (tidal volume).
2
150
mL
150
350
RESPIRATORY
CYCLE IN
ADULT
2200 mL
150
2200 mL
4
Dead space filled
with stale air
KEY
PO2 = 150 mm Hg (fresh air)
PO2 ~
~ 100 mm Hg (stale air)
150
mL
2200 mL
3
Figure 17-14
Ventilation
• Alveolar ventilation = ventilation rate  (tidal
volume – dead space volume)
Table 17-4
Ventilation
Table 17-5
Ventilation
Table 17-6
Ventilation
• As alveolar ventilation increases, alveolar
PO2 increases and PCO2 decreases
Figure 17-15
Ventilation
Table 17-7
Ventilation
• Local control mechanisms attempt to match
ventilation and perfusion
Figure 17-16a
Ventilation
Figure 17-16b
Ventilation
Figure 17-16c
Ventilation
• Auscultation = diagnostic technique
• Obstructive lung diseases
• Asthma
• Emphysema
• Chronic bronchitis
Summary
• Respiratory system
• Cellular respiration, external respiration,
respiratory system, upper respiratory tract,
pharynx, and larynx
• Lower respiratory tract, trachea, bronchi,
bronchioles, alveoli, Type I and Type II alveolar
cells
• Diaphragm, intercostal muscles, lung, pleural
sac, and pleural fluid
• Gas Laws: Dalton’s law and Boyle’s law
Summary
• Ventilation
• Tidal volume, vital capacity, residual volume,
and respiratory cycle
• Alveolar pressure, active expiration, intrapleural
pressures, compliance, elastance, surfactant,
bronchoconstriction, and bronchodilation
• Total pulmonary ventilation, alveolar ventilation,
hyperventilation, and hypoventilation