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Part 1 Structure and
Function of the Respiratory
System
When you can not breath, nothing
else matters
Slogan of the American Lung
Association
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Respiration is the process by which
the body takes in and utilizes
oxygen (O2) and gets rid of carbon
dioxide (CO2).
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An Overview of Key Steps in Respiration
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Respiration can be divided into
four major functional events
• Ventilation: Movement of air into and out of
lungs
• Gas exchange between air in lungs and blood
• Transport of oxygen and carbon dioxide in the
blood
• Internal respiration: Gas exchange between
the blood and tissues
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Respiratory System Functions
• Gas exchange: Oxygen enters blood and carbon dioxide
leaves
• Regulation of blood pH: Altered by changing blood carbon
dioxide levels
• Voice production: Movement of air past vocal folds makes
sound and speech
• Olfaction: Smell occurs when airborne molecules drawn
into nasal cavity
• Protection: Against microorganisms by preventing entry
and removing them
• Metabolism: Synthesize and metabolize different
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compounds (Nonrespiratory Function of the Lung)
Section I ANATOMY OF THE
RESPIRATORY TRACT
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Respiratory System Divisions
• Upper Airway
– Nose, pharynx,
larynx and
associated
structures
• Lower Airway
– trachea, bronchi,
lungs
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Conducting Zone
• All the structures air
passes through before
reaching the
respiratory zone.
• Cartilage holds tube
system open and
smooth muscle
controls tube
diameter
• Warms and
humidifies inspired
air.
• Filters and cleans:
Insert fig. 16.5
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Respiratory Zone
• Region of
gas exchange
between air
and blood.
• Includes
respiratory
bronchioles
and alveolar
sacs.
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Airway branching
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Section II BLOOD SUPPLY
TO THE LUNG
• Two separate blood supplies: pulmonary circulation
and bronchial circulation
• Pulmonary circulation
• Bronchial circulation
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Pulmonary circulation
• Brings deoxygenated blood from the right
ventricle to the gas-exchange units
• At the gas-exchanging units, oxygen is
picked up and carbon dioxide is removed
from the blood
• The oxygenated blood returned to the left
atrium for distribution to the rest of the
body
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Bronchial circulation
• Arise from the aorta
• Provides nourishments to the lung
parenchyma（肺实质）
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Section III MUSCLES OF RESPIRATION
• Inspiratory muscle:
• Diaphragm and Abdominal breathing （腹式呼吸）
• external intercostal muscle and thoracic breathing
（胸式呼吸）
• accessory muscle of inspiration
• Expiratory muscle
• relax during normal breathing
• Internal intercostal muscle
• Muscles of the abdominal wall
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Thoracic Walls and Muscles of Respiration
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Breathing Rate
• At rest: 10-20 breaths / minute
• During exercise: 40 - 45 at maximum
exercise in adults
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Thoracic Volume
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Mechanisms of Breathing:
How do we change the volume of the rib cage ?
To Inhale is an ACTIVE process
•External Intercostal Muscles
• Diaphragm
Rib Cage
Spine
Intercostals
Rib Contract
to Lift
Contract
Diaphragm
Volume
Ribs
Volume
Both actions occur simultaneously – otherwise not effective
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Pleura
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•Pleural fluid produced by pleural
membranes
–Acts as lubricant
–Helps hold parietal and visceral pleural
membranes together
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Ventilation
• Movement of air into and out of lungs
• Air moves from area of higher pressure to
area of lower pressure
• Pressure is inversely related to volume
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Alveolar Pressure Changes During
Respiration
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Principles of Breathing
Functional Unit: Chest Wall and Lung
Follows Boyle’s Law:
Pressure (P) x Volume (V) = Constant
Conducting
Airways
Lungs
Pleural Cavity
Gas Exchange
Very small space
Maintained at negative pressure
Transmits pressure changes
Allows lung and ribs to slide
Chest Wall
(muscle, ribs)
Pleural Cavity
Diaphragm
(muscle)
Imaginary Space between
Lungs and chest wall
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Principle of Breathing
Follows Boyle’s Law: PV= C
At Rest with mouth open Pb = Pi = 0
Pb
Airway Open
A
Pi
CW PS
D
1
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Principle of Breathing
Follows Boyle’s Law: PV= C
At Rest with mouth open Pb = Pi = 0
Inhalation:
- Increase Volume of Rib cage
- Decrease the pleural cavity pressure
- Decrease in Pressure inside (Pi)
lungs
CW
Pb
Airway Open
A
Pi
PS
D
2
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Principle of Breathing
Follows Boyle’s Law: PV= C
At Rest with mouth open Pb = Pi = 0
Inhalation:
Pb
Airway Open
A
- Pb outside is now greater than Pi
- Air flows down pressure gradient
- Until Pi = Pb
CW
Pi
PS
D
3
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Principle of Breathing
Follows Boyle’s Law: PV= C
At Rest with mouth open Pb = Pi = 0
Pb
Airway Open
A
Exhalation: Opposite Process
- Decrease Rib Cage Volume CW
Pi
PS
D
4
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Principle of Breathing
Follows Boyle’s Law: PV= C
At Rest with mouth open Pb = Pi = 0
Pb
Airway Open
A
Exhalation: Opposite Process
- Decrease Rib Cage Volume CW
- Increase in pleural
cavity pressure
- Increase Pi
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Pi
PS
D
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Principle of Breathing
Follows Boyle’s Law: PV= C
At Rest with mouth open Pb = Pi = 0
Pb
Airway Open
A
Exhalation: Opposite Process
- Decrease Rib Cage Volume CW
- Increase Pi
- Pi is greater than Pb
- Air flows down pressure gradient
- Until Pi = Pb again
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Pi
PS
D
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Section IV SURFACTANT AND
SURFACE TENSION
• Surface tension (表面张力）: a measure of
the attraction force of the surface molecules
per unit length of the material to which they
are attached
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Surface Tension
• Force exerted by fluid in alveoli to resist
distension
• Lungs secrete and absorb fluid, leaving a
very thin film of fluid.
• H20 molecules at the surface are attracted
to other H20 molecules by attractive forces.
– Force is directed inward, raising pressure in
alveoli.
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What is Surface Tension ?
Within Fluid
All forces balance
At surface
Unbalanced forces
Generate Tension
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Surface Tension
• Law of Laplace:
– Pressure in alveoli
–directly proportional
to surface tension
–inversely
proportional to radius
of alveoli
– if surface tension were
the same in all
alveolus....
Insert fig. 16.11
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Effect of Surface Tension on Alveoli size
Air Flow
Expand
Collapse
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Surfactant (表面活性物质）
• Phospholipid produced
by alveolar type II cells.
• Lowers surface tension.
– Reduces attractive
forces of hydrogen
bonding
– by becoming
interspersed between
H20 molecules.
• Surface tension in
alveoli is reduced.
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Area dependence of Surfactant action
Low S/unit Area
Saline
Slider - Change Surface Area
Increase
Area
Saline
Decrease
Area
High S/unit Area
Surfactant
Area
Tension
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Surfactant prevents alveolar collapse
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Volume L
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Saline Filled
3
Normal (with surfactant)
Without surfactant
RV
Pleural Pressure
0
0
- 15
- 30 cm H2O
Volume-pressure curves of lungs filled with
saline and with air (with or without surfactant) 40
Physiology Importance of Surfactant
• Reduce the work of breathing
• Stabilize alveoli
• Prevent collapse and sticking of
alveoli
• Maintain the dryness of the alveoli
• Prevent the edema of the alveoli
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