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Chapter 23
Respiratory System
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Respiration
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Occurs in several discrete stages…
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
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
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Respiratory System Divisions
• Upper tract
– Nose, pharynx and
associated structures
• Lower tract
– Larynx, trachea,
bronchi, lungs
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Nasal Cavity and Pharynx
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Nose and Pharynx
• Nose
– External nose
– Nasal cavity
• Functions
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Passageway for air
Cleans the air
Humidifies, warms air
Olfaction
Along with paranasal
sinuses are resonating
chambers for speech
• Pharynx
– Common opening for
digestive and
respiratory systems
– Three regions
• Nasopharynx
• Oropharynx
• Laryngopharynx
Larynx
• Functions
– Maintain an open passageway for air movement
– Epiglottis and vestibular folds prevent swallowed material
from moving into larynx
7 – Vocal folds are primary source of sound production
Vocal Folds
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Trachea
Insert Fig 23.5 all but b
• Windpipe
• Divides to form
– Primary bronchi
– Carina: Cough reflex
stops here…
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Tracheobronchial Tree
• Conducting zone
– Trachea to terminal bronchioles which is
ciliated for removal of debris
– Passageway for air movement
– Cartilage holds tube system open and smooth
muscle controls tube diameter
• Respiratory zone
– Respiratory bronchioles to alveoli
– Site for gas exchange
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Tracheobronchial Tree
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Bronchioles and Alveoli
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Alveolus and Respiratory
Membrane
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Lungs
• Two lungs: Principal organs of respiration
– Right lung: Three lobes
– Left lung: Two lobes
• Divisions
15 – Lobes, bronchopulmonary segments, lobules
Thoracic Walls
Muscles of Respiration
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Changing Thoracic Volume
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Pleura
• Pleural fluid produced by pleural membranes
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– Acts as lubricant
– Helps hold parietal and visceral pleural membranes
together
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
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Changing Alveolar Volume
• Lung recoil
– Causes alveoli to collapse resulting from
• Elastic recoil and surface tension
– Surfactant: Reduces tendency of lungs to collapse
– Surfactant = lipoprotein monomolecular layer lining inner
surfaces of lungs
Respiratory Distress Syndrome – premature infants (<7mo ages) do
not produce sufficient surfactant, lungs tend 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
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Normal Breathing Cycle
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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 (fluid buildup)
– Respiratory distress syndrome (premature infants)
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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
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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
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Spirometer and Lung
Volumes/Capacities
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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
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Physical Principles of Gas
Exchange
• Partial pressure
– The pressure exerted by each type of gas in a mixture
– Dalton’s law – total pressure of a gas mixture determined from %
of each gas present
(Air = N2 79%, O2 21% approx)
– Water vapor pressure
• Diffusion of gases through liquids
– Concentration of a gas in a liquid is determined by its partial
pressure (pp) and its solubility coefficient
– Henry’s law –[dissolved gas] = pp gas x solubility coefficient
Solubility = how easily a gas dissolves in liquid eg. CO2 about 24x more
soluble in water than O2
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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
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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
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• Carbon dioxide
– Moves from tissues
into tissue capillaries
– Moves from
pulmonary capillaries
into the alveoli
Changes in Partial Pressures
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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 (alkaline), a decrease in carbon
dioxide, or a decrease in temperature results in an
increase in the ability of hemoglobin to hold
oxygen
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Hemoglobin and Oxygen
Transport
• A shift of the curve to the right because of a
decrease in pH (acidic) , 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
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Oxygen-Hemoglobin
Dissociation Curve at Rest
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Oxygen-Hemoglobin
Dissociation Curve during Exercise
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Shifting the Curve
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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
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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
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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
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Respiratory Structures in Brainstem
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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.
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Modification of Ventilation
• Chemical control
• Cerebral and limbic
system
– Respiration can be
voluntarily controlled
and modified by
emotions
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– 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
Modifying Respiration
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Regulation of Blood pH and Gases
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Herring-Breuer Reflex
• Limits the degree of inspiration and prevents
overinflation of the lungs – mediated by stretch
receptors in bronchi/bronchiole walls
– 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
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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
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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
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