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Chapter 21
The Respiratory System
• Cells continually use O2
& release CO2
• Respiratory system
designed for gas
exchange
• Cardiovascular system
transports gases in blood
• Failure of either system
– rapid cell death from O2
starvation
Respiratory System Anatomy
• Nose
• Pharynx
• Larynx
• Trachea
• Bronchi
• Lungs
*Locations of infections
– upper respiratory tract is above vocal cords
– lower respiratory tract is below vocal cords
External Nasal Structures
• Skin, nasal bones, & cartilage lined with mucous membrane
• Openings called external nares or nostrils
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Nose -- Internal Structures
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Large chamber within the skull
Roof is made up of ethmoid and floor is hard palate
Internal nares (choanae) are openings to pharynx
Nasal septum is composed of bone & cartilage
Bony swelling or conchae on lateral walls
Functions of the Nasal Structures
• Olfactory epithelium for sense of smell
• Pseudostratified ciliated columnar with goblet
cells lines nasal cavity
– warms air due to high vascularity
– mucous moistens air & traps dust
– cilia move mucous towards pharynx
• Paranasal sinuses open into nasal cavity
– found in ethmoid, sphenoid, frontal & maxillary
– lighten skull & resonate voice
Pharynx
• Muscular tube (5 inch long) hanging from
skull
– skeletal muscle & mucous membrane
• Extends from internal nares to cricoid
cartilage
• Functions
– passageway for food and air
– resonating chamber for speech production
– tonsil (lymphatic tissue) in the walls protects
entryway into body
• Distinct regions -- nasopharynx, oropharynx
and laryngopharynx
Nasopharynx
• From choanae to soft palate
– openings of auditory (Eustachian) tubes from middle ear cavity
– adenoids or pharyngeal tonsil in roof
• Passageway for air only
Oropharynx
• From soft palate to epiglottis
– fauces is opening from mouth into oropharynx
– palatine tonsils found in side walls, lingual tonsil in
tongue
• Common passageway for food & air
Laryngopharynx
• Extends from epiglottis to cricoid cartilage
• Common passageway for food & air & ends as esophagus
inferiorly
Cartilages of the Larynx
• Thyroid cartilage forms Adam’s apple
• Epiglottis---leaf-shaped piece of elastic cartilage
– during swallowing, larynx moves upward
– epiglottis bends to cover glottis
• Cricoid cartilage---ring of cartilage attached to
top of trachea
• Pair of arytenoid cartilages sit upon cricoid
– many muscles responsible for their movement
– partially buried in vocal folds (true vocal cords)
Larynx
• Cartilage & connective tissue tube
• Anterior to C4 to C6
• Constructed of 3 single & 3 paired cartilages
Vocal Cords
• False vocal cords (ventricular folds) found above
vocal folds (true vocal cords)
• True vocal cords attach to arytenoid cartilages
The Structures of Voice Production
• True vocal cord contains both skeletal muscle
and an elastic ligament (vocal ligament)
• When 10 intrinsic muscles of the larynx
contract, move cartilages & stretch vocal cord
tight
• When air is pushed past tight ligament, sound
is produced (the longer & thicker vocal cord
in male produces a lower pitch of sound)
• The tighter the ligament, the higher the pitch
• To increase volume of sound, push air harder
Movement of Vocal Cords
• Opening and closing of the vocal folds occurs during
breathing and speech
Speech and Whispering
• Speech is modified sound made by the larynx.
• Speech requires pharynx, mouth, nasal cavity &
sinuses to resonate that sound
• Tongue & lips form words
• Pitch is controlled by tension on vocal folds
– pulled tight produces higher pitch
– male vocal folds are thicker & longer so vibrate
more slowly producing a lower pitch
• Whispering is forcing air through almost closed
rima glottidis -- oral cavity alone forms speech
Trachea
• Size is 5 in long & 1in diameter
• Extends from larynx to T5 anterior to the
esophagus and then splits into bronchi
• Layers
– mucosa = pseudostratified columnar with cilia & goblet
– submucosa = loose connective tissue & seromucous
glands
– hyaline cartilage = 16 to 20 incomplete rings
• open side facing esophagus contains trachealis m. (smooth)
• internal ridge on last ring called carina
– adventitia binds it to other organs
Trachea and Bronchial Tree
• Full extent of airways is visible starting at the
larynx and trachea
Chest x Ray
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Tracheostomy and Intubation
• Reestablishing airflow past an airway obstruction
– crushing injury to larynx or chest
– swelling that closes airway
– vomit or foreign object
• Tracheostomy is incision in trachea below cricoid
cartilage if larynx is obstructed
• Intubation is passing a tube from mouth or nose
through larynx and trachea
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Bronchi and Bronchioles
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Primary bronchi supply each lung
Secondary bronchi supply each lobe of the lungs (3 right + 2 left)
Tertiary bronchi supply each bronchopulmonary segment
Repeated branchings called bronchioles form a bronchial tree
Pleural Membranes & Pleural Cavity
• Visceral pleura covers lungs --- parietal pleura lines
ribcage & covers upper surface of diaphragm
• Pleural cavity is potential space between ribs & lungs
Gross Anatomy of Lungs
• Base, apex (cupula), costal surface, cardiac notch
• Oblique & horizontal fissure in right lung results in 3 lobes
• Oblique fissure only in left lung produces 2 lobes
Mediastinal Surface of Lungs
• Blood vessels & airways enter lungs at hilus
• Forms root of lungs
• Covered with pleura (parietal becomes visceral)
Structures within a Lobule of Lung
• Branchings of single
arteriole, venule &
bronchiole are wrapped by
elastic CT
• Respiratory bronchiole
– simple squamous
• Alveolar ducts surrounded
by alveolar sacs & alveoli
– sac is 2 or more alveoli
sharing a common opening
Cells Types of the Alveoli
• Type I alveolar cells
– simple squamous cells where gas exchange occurs
• Type II alveolar cells (septal cells)
– free surface has microvilli
– secrete alveolar fluid containing surfactant
• Alveolar dust cells
– wandering macrophages remove debris
Alveolar-Capillary Membrane
• Respiratory membrane = 1/2 micron thick
• Exchange of gas from alveoli to blood
• 4 Layers of membrane to cross
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alveolar epithelial wall of type I cells
alveolar epithelial basement membrane
capillary basement membrane
endothelial cells of capillary
• Vast surface area = handball court
Details of Respiratory Membrane
• Find the 4 layers that comprise the respiratory
membrane
Breathing or Pulmonary Ventilation
• Air moves into lungs when pressure inside
lungs is less than atmospheric pressure
– How is this accomplished?
• Air moves out of the lungs when pressure
inside lungs is greater than atmospheric
pressure
– How is this accomplished?
• Atmospheric pressure = 1 atm or 760mm Hg
Boyle’s Law
• As the size of closed container decreases, pressure
inside is increased
• The molecules have less wall area to strike so the
pressure on each inch of area increases.
Dimensions of the Chest Cavity
• Breathing in requires muscular activity & chest size changes
• Contraction of the diaphragm flattens the dome and
increases the vertical dimension of the chest
Quiet Inspiration
• Diaphragm moves 1 cm & ribs lifted by muscles
• Intrathoracic pressure falls and 2-3 liters inhaled
Quiet Expiration
• Passive process with no muscle action
• Elastic recoil & surface tension in alveoli pulls inward
• Alveolar pressure increases & air is pushed out
Labored Breathing
• Forced expiration
– abdominal mm force
diaphragm up
– internal intercostals
depress ribs
• Forced inspiration
– sternocleidomastoid,
scalenes & pectoralis
minor lift chest
upwards as you gasp
for air
Intrathoracic
Pressures
• Always subatmospheric (756 mm Hg)
• As diaphragm contracts intrathoracic pressure decreases even
more (754 mm Hg)
• Helps keep parietal & visceral pleura stick together
Summary of Breathing
• Alveolar pressure decreases & air rushes in
• Alveolar pressure increases & air rushes out
Alveolar Surface Tension
• Thin layer of fluid in alveoli causes
inwardly directed force = surface tension
– water molecules strongly attracted to each other
• Causes alveoli to remain as small as
possible
• Detergent-like substance called surfactant
produced by Type II alveolar cells
– lowers alveolar surface tension
– insufficient in premature babies so that alveoli
collapse at end of each exhalation
Pneumothorax
• Pleural cavities are sealed cavities not open
to the outside
• Injuries to the chest wall that let air enter
the intrapleural space
– causes a pneumothorax
– collapsed lung on same side as injury
– surface tension and recoil of elastic fibers
causes the lung to collapse
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Compliance of the Lungs
• Ease with which lungs & chest wall expand
depends upon elasticity of lungs & surface
tension
• Some diseases reduce compliance
– tuberculosis forms scar tissue
– pulmonary edema --- fluid in lungs & reduced
surfactant
– paralysis
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Airway Resistance
• Resistance to airflow depends upon
airway size
– increase size of chest
• airways increase in diameter
– contract smooth muscles in airways
• decreases in diameter
Breathing Patterns
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Eupnea = normal quiet breathing
Apnea = temporary cessation of breathing
Dyspnea =difficult or labored breathing
Tachypnea = rapid breathing
Diaphragmatic breathing = descent of
diaphragm causes stomach to bulge during
inspiration
• Costal breathing = just rib activity involved
Modified Respiratory Movements
• Coughing
– deep inspiration, closure of rima glottidis & strong
expiration blasts air out to clear respiratory passages
• Hiccuping
– spasmodic contraction of diaphragm & quick
closure of rima glottidis produce sharp inspiratory
sound
Lung Volumes and Capacities
• Tidal volume = amount air moved during quiet breathing
• MVR= minute ventilation is amount of air moved in a minute
• Reserve volumes ---- amount you can breathe either in or out above
that amount of tidal volume
• Residual volume = 1200 mL permanently trapped air in system
• Vital capacity & total lung capacity are sums of the other volumes
Dalton’s Law
• Each gas in a mixture of gases exerts its
own pressure
– as if all other gases were not present
– partial pressures denoted as p
• Total pressure is sum of all partial pressures
– atmospheric pressure (760 mm Hg) = pO2 +
pCO2 + pN2 + pH2O
– to determine partial pressure of O2-- multiply
760 by % of air that is O2 (21%) = 160 mm Hg
What is Composition of Air?
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Air = 21% O2, 79% N2 and .04% CO2
Alveolar air = 14% O2, 79% N2 and 5.2% CO2
Expired air = 16% O2, 79% N2 and 4.5% CO2
Observations
– alveolar air has less O2 since absorbed by blood
– mystery-----expired air has more O2 & less CO2 than
alveolar air?
– Anatomical dead space = 150 ml of 500 ml of tidal
volume
Henry’s Law
• Quantity of a gas that will dissolve in a liquid
depends upon the amount of gas present and its
solubility coefficient
– explains why you can breathe compressed air while
scuba diving despite 79% Nitrogen
• N2 has very low solubility unlike CO2 (soda cans)
• dive deep & increased pressure forces more N2 to dissolve in
the blood (nitrogen narcosis)
• decompression sickness if come back to surface too fast or
stay deep too long
• Breathing O2 under pressure dissolves more O2 in
blood
Hyperbaric Oxygenation
• Clinical application of Henry’s law
• Use of pressure to dissolve more O2 in the blood
– treatment for patients with anaerobic bacterial
infections (tetanus and gangrene)
– anaerobic bacteria die in the presence of O2
• Hyperbaric chamber pressure raised to 3 to 4
atmospheres so that tissues absorb more O2
• Used to treat heart disorders, carbon monoxide
poisoning, cerebral edema, bone infections, gas
embolisms & crush injuries
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Respiration
• 4 distinct processes collectively called
respiration must occur: Pulmonary
Ventilation, External Respiration, Transport
of Respiratory Gases, and Internal
Respiration
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1. Pulmonary Ventilation
• Movement of air into and out of the lungs
so that the gases in the air sacs (alveoli) of
the lungs are continuously changed and
refreshed
• The air movement is called ventilation
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2. External Respiration
• Gas exchange (oxygen loading and carbon
dioxide unloading) between the blood and
the air-filled chambers of the lungs
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External Respiration
• Gases diffuse from areas
of high partial pressure to
areas of low partial
pressure
• Exchange of gas between
air & blood
• Deoxygenated blood
becomes saturated
• Compare gas movements
in pulmonary capillaries
to tissue capillaries
Rate of Diffusion of Gases
• Depends upon partial pressure of gases in air
– p O2 at sea level is 160 mm Hg
– 10,000 feet is 110 mm Hg / 50,000 feet is 18 mm Hg
• Large surface area of our alveoli
• Diffusion distance is very small
• Solubility & molecular weight of gases
– O2 smaller molecule diffuses somewhat faster
– CO2 dissolves 24X more easily in water so net
outward diffusion of CO2 is much faster
– disease produces hypoxia before hypercapnia
– lack of O2 before too much CO2
3. Transport of Respiratory Gases
• Transport of oxygen and carbon dioxide
between the lungs and tissue cells of the
body
• Accomplished by the cardiovascular
system, which uses blood as the
transporting fluid
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4. Internal Respiration
• Gas exchanges (oxygen unloading and
carbon dioxide loading) between the
systemic blood and tissue cells
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Internal Respiration
• Exchange of gases between
blood & tissues
• Conversion of oxygenated
blood into deoxygenated
• Observe diffusion of O2
inward
– at rest 25% of available O2
enters cells
– during exercise more O2 is
absorbed
• Observe diffusion of CO2
outward
Oxygen Transport in the Blood
• Oxyhemoglobin contains 98.5% chemically
combined oxygen and hemoglobin
– inside red blood cells
• Does not dissolve easily in water
– only 1.5% transported dissolved in blood
• Only the dissolved O2 can diffuse into tissues
• Factors affecting dissociation of O2 from
hemoglobin are important
• Oxygen dissociation curve shows levels of
saturation and oxygen partial pressures
Hemoglobin and Oxygen Partial Pressure
• Blood is almost fully
saturated at pO2 of 60mm
– people OK at high altitudes
& with some disease
• Between 40 & 20 mm Hg,
large amounts of O2 are
released as in areas of
need like contracting
muscle
Acidity & Oxygen Affinity for Hb
• As acidity
increases, O2
affinity for
Hb decreases
• Bohr effect
• H+ binds to
hemoglobin
& alters it
• O2 left
behind in
needy tissues
pCO2 & Oxygen Release
• As pCO2 rises
with exercise,
O2 is released
more easily
• CO2 converts to
carbonic acid &
becomes H+ and
bicarbonate ions
& lowers pH.
Temperature & Oxygen Release
• As temperature
increases, more
O2 is released
• Metabolic activity
& heat
• More BPG, more
O2 released
– RBC activity
– hormones like
thyroxine &
growth hormone
Oxygen Affinity & Fetal Hemoglobin
• Differs from adult
in structure &
affinity for O2
• When pO2 is low,
can carry more
O2
• Maternal blood in
placenta has less
O2
Carbon Monoxide Poisoning
• CO from car exhaust & tobacco smoke
• Binds to Hb heme group more successfully
than O2
• CO poisoning
• Treat by administering pure O2
Carbon Dioxide Transport
• 100 ml of blood carries 55 ml of CO2
• Is carried by the blood in 3 ways
– dissolved in plasma
– combined with the globin part of Hb molecule
forming carbaminohemoglobin
– as part of bicarbonate ion
• CO2 + H2O combine to form carbonic acid that
dissociates into H+ and bicarbonate ion
Summary of Gas Exchange & Transport
Role of the Respiratory Center
• Respiratory mm.
controlled by
neurons in pons &
medulla
• 3 groups of neurons
– medullary
rhythmicity
– pneumotaxic
– apneustic centers
Medullary Rhythmicity Area
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Controls basic rhythm of respiration
Inspiration for 2 seconds, expiration for 3
Autorhythmic cells active for 2 seconds then inactive
Expiratory neurons inactive during most quiet breathing
only active during high ventilation rates
Regulation of Respiratory Center
• Cortical Influences
– voluntarily alter breathing patterns
– limitations are buildup of CO2 & H+ in blood
– inspiratory center is stimulated by increase in
either
– if you hold breathe until you faint----breathing
will resume
Chemical Regulation of Respiration
• Central chemoreceptors in medulla
– respond to changes in H+ or pCO2
– hypercapnia = slight increase in pCO2 is noticed
• Peripheral chemoreceptors
– respond to changes in H+ , pO2 or PCO2
– aortic body---in wall of aorta
• nerves join vagus
– carotid bodies--in walls of common carotid arteries
• nerves join glossopharyngeal nerve
Negative Feedback Regulation of Breathing
• Negative feedback control
of breathing
• Increase in arterial pCO2
• Stimulates receptors
• Inspiratory center
• Muscles of respiration
contract more frequently &
forcefully
• pCO2 Decreases
Regulation of Ventilation Rate and Depth
Types of Hypoxia
• Deficiency of O2 at tissue level
• Types of hypoxia
– hypoxic hypoxia--low pO2 in arterial blood
• high altitude, fluid in lungs & obstructions
– anemic hypoxia--too little functioning Hb
• hemorrhage or anemia
– ischemic hypoxia--blood flow is too low
– histotoxic hypoxia--cyanide poisoning
• blocks metabolic stages & O2 usage
Respiratory Influences & Reflex Behaviors
• Quick breathing rate response to exercise
– input from proprioceptors
• Inflation Reflex (Hering-Breurer reflex)
– big deep breath stretching receptors produces urge
to exhale
• Factors increasing breathing rate
– emotional anxiety, temperature increase or drop in
blood pressure
• Apnea or cessation of breathing
– by sudden plunge into cold water, sudden pain,
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irritation of airway
Exercise and the Respiratory System
• During exercise, muscles consume large
amounts of O2 & produce large amounts CO2
• Pulmonary ventilation must increase
– moderate exercise increases depth of breathing,
– strenuous exercise also increases rate of breathing
• Abrupt changes at start of exercise are neural
– anticipation & sensory signals from proprioceptors
– impulses from motor cortex
• Chemical & physical changes are important
– decrease in pO2, increase in pCO2 & increased
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temperature
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Smokers Lowered Respiratory Efficiency
• Smoker is easily “winded” with moderate
exercise
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nicotine constricts terminal bronchioles
carbon monoxide in smoke binds to hemoglobin
irritants in smoke cause excess mucus secretion
irritants inhibit movements of cilia
in time destroys elastic fibers in lungs & leads to
emphysema
• trapping of air in alveoli & reduced gas exchange
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Developmental Anatomy of Respiratory System
• 4 weeks endoderm of
foregut gives rise to
lung bud
• Differentiates into
epithelial lining of
airways
• 6 months closed-tubes
swell into alveoli of
lungs
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Aging & the Respiratory System
• Respiratory tissues & chest wall become more
rigid
• Vital capacity decreases to 35% by age 70.
• Decreases in macrophage activity
• Diminished ciliary action
• Decrease in blood levels of O2
• Result is an age-related susceptibility to
pneumonia or bronchitis
Disorders of the Respiratory System
• Asthma
• Chronic obstructive pulmonary disease
– Emphysema
– Chronic bronchitis
– Lung cancer
• Pneumonia
• Tuberculosis
• Coryza and Influenza
• Pulmonary Edema
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Cystic
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Homework
• A1, A2, A5, A6, B4, B8, B10, C2, C3, C10,
D1
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