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Respiratory System
23-1
Respiration
• Ventilation: Movement of air into and out of
lungs
• External respiration: 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
• Cellular Respiration: The use of O2 to produce
ATP via Glycolysis, TCA cycle, & ETS
23-2
Respiratory System Functions
• Gas exchange: Oxygen enters blood and carbon
dioxide leaves
• Regulation of blood pH: Altered by changing blood
carbon dioxide levels Carbonic acid Buffer system
• Sound production: Movement of air past vocal folds
makes sound and speech
• Olfaction: Smell occurs when airborne molecules
drawn into nasal cavity
• Thermoregulation: Heating and cooling of body
• Protection: Against microorganisms by preventing
entry and removing them
23-3
Respiratory System Divisions
• Upper tract
– Nose, pharynx and
associated structures,
Larynx.
• Lower tract
– trachea, bronchi, lungs
23-4
Nasal Cavity and Pharynx
23-5
Nasal Cavity and Pharynx
23-6
Nose and Pharynx
• Nose
– External nose
– Nasal cavity
• Functions
–
–
–
–
–
Passageway for air
Cleans the air
Humidifies, warms air
Smell
Along with paranasal
sinuses are resonating
chambers for speech
• Pharynx
– Common opening for
digestive and
respiratory systems
– Skull-C6
– Three regions
• Nasopharynx
• Oropharynx
• Laryngopharynx
23-7
Larynx
• Functions
– Maintain an open passageway for air movement
– Epiglottis and vestibular folds prevent swallowed material
from moving into larynx
– Vocal folds are primary source of sound production
23-8
Vocal Folds
23-9
Trachea
Insert Fig 23.5 all but b
• Windpipe
• Divides to form
– Rt , Lt Primary
bronchi
– Carina: Cough reflex
23-10
Tracheobronchial Tree
• Non-Acinus -Conducting zone
– Trachea to terminal bronchioles which is ciliated for
removal of debris, mucus lined
– Passageway for air movement controlled by smooth
muscle at end of terminal bronchioles
– Cartilage holds tube system open and smooth
muscle controls tube diameter
• Acinus Portion - Respiratory zone
– Respiratory bronchioles to alveoli
– Site for gas exchange Area the size of a football
field
23-11
Tracheobronchial Tree
23-12
Bronchioles and Alveoli
23-13
Alveolus and Respiratory
Membrane
23-14
Lungs
• Two lungs: Principal organs of respiration
– Right lung: Three lobes, shorter, broader, and has a greater volume.
– Left lung: Two lobes, is longer and narrower than the right lung
• Divisions
– Lobes, bronchopulmonary segments, lobules
23-15
Lungs
• The only point of attachment for each lung is at the hilum, or
root, on the medial side. This is where the bronchi, blood
vessels, lymphatics, and nerves enter the lungs.
• Each lung is enclosed by a double-layered serous membrane,
called the pleura. The visceral pleura is firmly attached to the
surface of the lung. At the hilum, the visceral pleura is
continuous with the parietal pleura that lines the wall of the
thorax. The small space between the visceral and parietal pleurae
is the pleural cavity. It contains a thin film of serous fluid that is
produced by the pleura. The fluid acts as a lubricant to reduce
friction as the two layers slide against each other, and it helps to
hold the two layers together as the lungs inflate and deflate.
23-16
Thoracic Walls
Muscles of Respiration
23-17
Thoracic Volume
23-18
Pleura
• Pleural fluid produced by pleural membranes
– Acts as lubricant
– Helps hold parietal and visceral pleural membranes
together
23-19
Pressure – Volume Relationships
• As vol. , pressure 
• As vol. , pressure 
• This is given by Boyle’s
Law which says:
P1V1 = P2V2
• Why does this occur?
– Remember, pressure
equals force/area
P = Force/Area
So, in this equation as A
gets larger P must get
smaller.
23-20
23-21
Ventilation
• Movement of air into and out of lungs via
negative pressure pump mechanism
• Air moves from area of higher pressure
outside the lung to area of lower pressure
created in the thorax and lungs by diaphram
• Pressure is inversely related to volume in
that as pressure goes down lung volume
goes up
23-22
Inspiration
• Begins with the contraction of
the diaphragm and the
external intercostals
• This causes thoracic volume
to 
• Which causes lung volume to

• Which causes lung pressure to

• Now Palv is <Patm so air will
flow down its pressure
gradient and enter the lungs.
• Inspiration ends when
Palv=Patm
23-23
Inspiration
Active process
involving the
diaphragm and
intercostal
muscles
23-24
3 Muscle Groups of Inhalation
1. Diaphragm:
–
–
contraction draws air into lungs
75% of normal air movement
2. External intracostal muscles:
–
–
assist inhalation
25% of normal air movement
3. Accessory muscles assist in elevating ribs:
–
–
–
–
sternocleidomastoid
serratus anterior
pectoralis minor
scalene muscles
23-25
• Quiet expiration is a
passive process that is
due to the elasticity of
the lungs.
• Forced expiration is an
active process due to
contraction of oblique
and transverse
abdominus muscles,
internal intercostals, and
the latissimus dorsi.
Expiration
23-26
Expiration
Usually passive
Can become
active
Using internal
intercoastal and
abdominal
muscles
23-27
Alveolar Pressure Changes
23-28
Changing Alveolar Volume
• Lung recoil
– Causes alveoli to collapse resulting from
• Elastic recoil and surface tension : Pneumothorax
– Surfactant: Reduces tendency of lungs to collapse
• Pleural pressure
– Negative pressure can cause alveoli to expand
– Pneumothorax is an opening between pleural
cavity and air that causes a loss of pleural
pressure
23-29
Compliance
• Measure of the ease with which lungs and
thorax expand
– The greater the compliance, the easier it is for a
change in pressure to cause expansion
– A lower-than-normal compliance means the
lungs and thorax are harder to expand
• Conditions that decrease compliance
– Pulmonary fibrosis
– Pulmonary edema
– Respiratory distress syndrome.
23-30
Alveolar Membrane
1) Surfactant and water layer
2) Alveolar wall- Simple squamous
epithelium
3) Basement membrane of alveolar wall
4) Interstitial space
5) Capillary wall- Simple squamous
epithelium
6) Basement membrane of cap wall.
23-31
Alveolar Capillary Membrane
23-32
The factors that effect rate of gas
exchange
– Partial pressure gradients of O2 and
CO2
– Surface area of alveolar membrane
– Thickness of capillary-alveolar
membrane
– Ventilation- perfusion mismatch
23-33
Pulmonary Volumes
• Tidal volume
– Volume of air inspired or expired during a normal inspiration or
expiration
• Inspiratory reserve volume
– Amount of air inspired forcefully after inspiration of normal tidal
volume
• Expiratory reserve volume
– Amount of air forcefully expired after expiration of normal tidal
volume
• Residual volume
– Volume of air remaining in respiratory passages and lungs after the
most forceful expiration
23-34
Pulmonary Capacities
• Inspiratory capacity
– Tidal volume plus inspiratory reserve volume
• Functional residual capacity
– Expiratory reserve volume plus the residual volume
• Vital capacity
– Sum of inspiratory reserve volume, tidal volume, and expiratory
reserve volume
• Total lung capacity
– Sum of inspiratory and expiratory reserve volumes plus the tidal
volume and residual volume
23-35
Pulmonary Capacities
• Inspiratory capacity is the total amt of air that can
be inspired after a tidal expiration:
IC = TV + IRV
• Functional residual capacity is the amt of air in the
lungs after a tidal expiration:
FRC = ERV + RV
• Vital capacity is the total amt of exchangeable air:
VC = TV+IRV+ERV
• Total lung capacity is the sum of all lung volumes
and is normally around 6L in males:
23-36
TLC = VC + RV
Spirometer and Lung
Volumes/Capacities
23-37
Lung Capacities
Lung Volumes:
•TV
•IRV
•ERV
•RV
Lung Capacities:
•VC
•FRC
•TLC
•IC
23-38
Minute and Alveolar Ventilation
• Minute ventilation: Total amount of air moved
into and out of respiratory system per minute
• Respiratory rate or frequency: Number of
breaths taken per minute
• Anatomic dead space: Part of respiratory
system where gas exchange does not take place
• Alveolar ventilation: How much air per minute
enters the parts of the respiratory system in
which gas exchange takes place
23-39
Physical Principles of Gas
Exchange
• Partial pressure
– The pressure exerted by each type of gas in a mixture
– Dalton’s law
– Water vapor pressure
• Diffusion of gases through liquids
– Concentration of a gas in a liquid is determined by its
partial pressure and its solubility coefficient
– Henry’s law
23-40
Physical Principles of Gas
Exchange
• Diffusion of gases through the respiratory
membrane
– Depends on membrane’s thickness, the diffusion coefficient
of gas, surface areas of membrane, partial pressure of gases
in alveoli and blood
• Relationship between ventilation and
pulmonary capillary flow
– Increased ventilation or increased pulmonary capillary blood
flow increases gas exchange
– Physiologic shunt is deoxygenated blood returning from
lungs
23-41
Oxygen and Carbon Dioxide
Diffusion Gradients
• Oxygen
– Moves from alveoli into
blood. Blood is almost
completely saturated
with oxygen when it
leaves the capillary
– P02 in blood decreases
because of mixing with
deoxygenated blood
– Oxygen moves from
tissue capillaries into the
tissues
• Carbon dioxide
– Moves from tissues
into tissue capillaries
– Moves from
pulmonary capillaries
into the alveoli.
23-42
Gas Exchange
23-43
23-44
Changes in Partial Pressures
23-45
Hemoglobin and 02 Transport
• 280 million
hemoglobin/ RBC.
• Each hemoglobin has 4
polypeptide chains and
4 hemes.
• Each heme has 1 atom
iron that can combine
with 1 molecule 02.
23-46
Hemoglobin
• Hemoglobin production controlled by
erythropoietin.
• Production stimulated by P02 delivery to kidneys.
• Loading/unloading depends:
– P02 of environment.
– Affinity between hemoglobin and 02.
23-47
Hemoglobin and Oxygen Transport
• Oxygen is transported by hemoglobin (98.5%) and
is dissolved in plasma (1.5%)
• Oxygen-hemoglobin dissociation curve shows that
hemoglobin is almost completely saturated when
P02 is 80 mm Hg or above. At lower partial
pressures, the hemoglobin releases oxygen.
• A shift of the curve to the left because of an
increase in pH, a decrease in carbon dioxide, or a
decrease in temperature results in an increase in
the ability of hemoglobin to hold oxygen
23-48
Hemoglobin and Oxygen
Transport
• A shift of the curve to the right because of a
decrease in pH, an increase in carbon dioxide, or
an increase in temperature results in a decrease in
the ability of hemoglobin to hold oxygen
• The substance 2.3-bisphosphoglycerate increases
the ability of hemoglobin to release oxygen
• Fetal hemoglobin has a higher affinity for oxygen
than does maternal
23-49
23-50
Shifting the Curve
23-51
C02 Transport
• C02 transported in the blood:
– HC03- (70%).
– Dissolved C02 (10%).
– Carbaminohemoglobin (20%).
23-52
23-53
23-54
Transport of Carbon Dioxide
• Carbon dioxide is transported as bicarbonate ions
(70%) in combination with blood proteins (23%)
and in solution with plasma (7%)
• Hemoglobin that has released oxygen binds more
readily to carbon dioxide than hemoglobin that has
oxygen bound to it (Haldane effect)
• In tissue capillaries, carbon dioxide combines with
water inside RBCs to form carbonic acid which
dissociates to form bicarbonate ions and hydrogen
ions
23-55
Transport of Carbon Dioxide
• In lung capillaries, bicarbonate ions and hydrogen
ions move into RBCs and chloride ions move out.
Bicarbonate ions combine with hydrogen ions to
form carbonic acid. The carbonic acid is
converted to carbon dioxide and water. The
carbon dioxide diffuses out of the RBCs.
• Increased plasma carbon dioxide lowers blood pH.
The respiratory system regulates blood pH by
regulating plasma carbon dioxide levels
23-56
Carbon Dioxide Transport
and Chloride Movement
23-57
Respiratory Areas in Brainstem
• Medullary respiratory center
– Dorsal groups stimulate the diaphragm
– Ventral groups stimulate the intercostal and
abdominal muscles
• Pontine (pneumotaxic) respiratory group
– Involved with switching between inspiration
and expiration
23-58
Respiratory Structures in Brainstem
23-59
Rhythmic Ventilation
• Starting inspiration
– Medullary respiratory center neurons are continuously active
– Center receives stimulation from receptors and simulation from parts of
brain concerned with voluntary respiratory movements and emotion
– Combined input from all sources causes action potentials to stimulate
respiratory muscles
• Increasing inspiration
– More and more neurons are activated
• Stopping inspiration
– Neurons stimulating also responsible for stopping inspiration and receive
input from pontine group and stretch receptors in lungs. Inhibitory
neurons activated and relaxation of respiratory muscles results in
expiration.
23-60
Modification of Ventilation
• Chemical control
• Cerebral and limbic
system
– Respiration can be
voluntarily controlled
and modified by
emotions
– Carbon dioxide is major
regulator
• Increase or decrease in pH
can stimulate chemosensitive area, causing a
greater rate and depth of
respiration
– Oxygen levels in blood
affect respiration when a
50% or greater decrease
from normal levels exists
23-61
Modifying Respiration
23-62
Regulation of Blood pH and Gases
23-63
Herring-Breuer Reflex
• Limits the degree of inspiration and
prevents overinflation of the lungs
– Infants
• Reflex plays a role in regulating basic rhythm of
breathing and preventing overinflation of lungs
– Adults
• Reflex important only when tidal volume large as in
exercise
23-64
Ventilation in Exercise
• Ventilation increases abruptly
– At onset of exercise
– Movement of limbs has strong influence
– Learned component
• Ventilation increases gradually
– After immediate increase, gradual increase occurs
(4-6 minutes)
– Anaerobic threshold is highest level of exercise
without causing significant change in blood pH
• If exceeded, lactic acid produced by skeletal muscles
23-65
Effects of Aging
• Vital capacity and maximum minute
ventilation decrease
• Residual volume and dead space increase
• Ability to remove mucus from respiratory
passageways decreases
• Gas exchange across respiratory membrane
is reduced.
23-66
Ventilation Patterns
•
•
•
•
•
•
•
•
•
Eupnea - Normal, quiet breathing
Dyspnea - Difficult breathing
Apnea - absence of breathing
Tachypnea - Rapid breathing rate
Bradypnea - Slow breathing
Hyperpnea - Deep breathing
Hypopnea - Shallow breathing
Hyperventilation - Rapid, deep breathing
Cheyne-Stokes breathing - periods of apnea
interspersed with hyperpnea
23-67