Chapter 7
The Respiratory System
Copyright 2010, John Wiley & Sons, Inc.
Respiration: Three Major Steps
1. Pulmonary ventilation

Moving air in and out of lungs
2. External respiration

Gas exchange between alveoli and blood
3. Internal respiration

Gas exchange between blood and cells
Copyright 2010, John Wiley & Sons, Inc.
Organs of the Respiratory System
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Upper respiratory system
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Lower respiratory system
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Nose and pharynx
Trachea, larynx, bronchi, bronchioles, and lungs
“Conducting zone” consists of
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All airways that carry air to lungs:
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Nose, pharynx, trachea, larynx, bronchi, bronchioles,
and terminal bronchioles
“Respiratory zone”

Sites within lungs where gas exchange occurs

Respiratory bronchioles, alveolar ducts, alveolar sacs,
and alveoli
Copyright 2010, John Wiley & Sons, Inc.
Organs of the Respiratory System
Copyright 2010, John Wiley & Sons, Inc.
Upper Respiratory System: Nose
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Structure
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External nares  nasal cavity  internal nares
Nasal septum divides nose into two sides
Nasal conchae covered by mucous membrane
Functions
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Warm, humidify, filter/trap dust and microbes
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Mucus and cilia of epithelial cells lining nose
Detect olfactory stimuli
Modify vocal sounds
Copyright 2010, John Wiley & Sons, Inc.
Upper Respiratory System: Pharynx
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Known as the “throat”
Structure
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Funnel-shaped tube from internal nares to larynx
3 parts
Three regions (with tonsils in the upper two)
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Upper: nasopharynx; posterior to nose
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Middle: oropharynx; posterior to mouth
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Adenoids and openings of auditory (Eustachian) tubes
Palatine and lingual tonsils are here
Lower: laryngeal pharynx

Connects with both esophagus and larynx: food and air
Copyright 2010, John Wiley & Sons, Inc.
Copyright 2010, John Wiley & Sons, Inc.
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Respiratory System: Head and Neck
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Lower Respiratory System: Larynx
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“Voice box”
Made largely of cartilage
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Thyroid cartilage: V-shaped
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Epiglottis: leaf-shaped piece; covers airway
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“Adam's apple”: projects more anteriorly in males
Vocal cords “strung” here (and to arytenoids)
During swallowing, larynx moves up so epiglottis covers
opening into trachea
Cricoid cartilage: inferior most portion
Arytenoids (paired, small) superior to cricoid
Copyright 2010, John Wiley & Sons, Inc.
Lower Respiratory System: Larynx
Copyright 2010, John Wiley & Sons, Inc.
Voice Production

Mucous membrane of larynx forms two pairs
of folds
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Upper = false vocal cords
Lower = true vocal cords
Contain elastic ligaments
 When muscles pull elastic ligaments tight, vocal
cords vibrate  sounds in upper airways
 Pitch adjusted by tension of true vocal cords
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Lower pitch of male voice

Vocal cords longer and thicker; vibrate more
slowly
Copyright 2010, John Wiley & Sons, Inc.
Lower Respiratory System: Trachea
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“Windpipe”
Location
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Structure
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Anterior to esophagus and thoracic vertebrae
Extends from end of larynx to primary bronchi
Lined with pseudostratified ciliated mucous
membrane: traps and moves dust upward
C-shaped rings of cartilage support trachea, keep
lumen open during exhalation
Tracheostomy: opening in trachea for tube
Copyright 2010, John Wiley & Sons, Inc.
Lower Respiratory System: Bronchi,
Bronchioles
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Structure of bronchial tree
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Bronchi contain cartilage rings
Primary bronchi enter the lungs medially
In lungs, branching secondary bronchi
 One for each lobe of lung: 3 in right, 2 in left
Tertiary bronchi    terminal bronchioles
These smaller airways
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
Have less cartilage, more smooth muscle. In
asthma, these airways can close.
Can be bronchodilated by sympathetic nerves,
epinephrine, or related medications.
Copyright 2010, John Wiley & Sons, Inc.
Lower Respiratory System: Lungs
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Two lungs: left and right
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Right lung has 3 lobes
Left lung has 2 lobes and cardiac notch
Lungs surrounded by pleural membrane
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Parietal pleura attached to diaphragm and lining
thoracic wall
Visceral pleura attached to lungs
Pleural cavity with little fluid between pleurae
Broad bottom of lungs = base; pointy top = apex
Copyright 2010, John Wiley & Sons, Inc.
Lung Lobes
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Divided into lobules fed by tertiary bronchi
Further divisions  terminal bronchioles
 Respiratory bronchioles
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Lined with nonciliated epithelium
 Alveolar ducts
 Alveolar sacs
 Surrounded by alveoli
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Lung Lobes
Copyright 2010, John Wiley & Sons, Inc.
Lower Respiratory System: Alveoli
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Cup-shaped outpouchings of alveolar sacs
Alveoli: composed of three types of cells
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Lined with thin alveolar cells (simple squamous);
sites of gas exchange
Scattered surfactant-secreting cells. Surfactant:
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Lowers surface tension (keeps alveoli from collapsing)
Humidifies (keeps alveoli from drying out)
Alveolar macrophages: “cleaners”
Respiratory membrane: alveoli + capillary

Gases diffuse across these thin epithelial layers:
air  blood
Copyright 2010, John Wiley & Sons, Inc.
Lobule of the Lung
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Lobule of the Lung
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Structure of an Alveolus
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Respiration Step: 1. Pulmonary Ventilation

Air flows: atmosphere   lungs due to
difference in pressure related to lung volume
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Inhalation: diaphragm + external intercostals
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Lung volume changes due to respiratory muscles
Diaphragm contracts (moves downward)   lung
volume
Cohesion between parietal-visceral pleura 
 lung volume as thorax volume .
Copyright 2010, John Wiley & Sons, Inc.
Exhalation

Exhalation is normally passive process due to
muscle relaxation
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Diaphragm relaxes and rises   lung volume
External intercostals relax   lung volume
Active exhalation: exhale forcefully

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Example: playing wind instrument
Uses additional muscles: internal intercostals,
abdominal muscles
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Muscles of Inhalation and Exhalation
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Muscles of Inhalation and Exhalation
Copyright 2010, John Wiley & Sons, Inc.
Volume-Pressure Changes in Lungs
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Volume and pressure are inversely related
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As  lung volume  alveolar pressure
As  lung volume  alveolar pressure
Contraction of diaphragm  lowers diaphragm
  lung volume  alveolar pressure so it is <
atmospheric pressure  air enters lungs =
inhalation
Relaxation of diaphragm  raises diaphragm 
 lung volume   alveolar pressure so it is >
atmospheric pressure  air leaves lungs =
exhalation
Copyright 2010, John Wiley & Sons, Inc.
Volume-Pressure Changes in Lungs
Copyright 2010, John Wiley & Sons, Inc.
Air Flow Terms
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Frequency = breaths/min; normal: 12
Tidal volume (TV) = volume moved in one
breath. Normal ~ 500 ml
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About 70% of TV reaches alveoli (350 ml)
Only this amount is involved in gas exchange
30% in airways = anatomic dead space
Minute ventilation (MV) = f x TV = 6000
mL/min
Copyright 2010, John Wiley & Sons, Inc.
Lung Volumes
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Measured by spirometer
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Inspiratory reserve volume (ERV) = volume of air
that can be inhaled beyond tidal volume (TV)
Expiratory reserve volume (IRV) = volume of air
that can be exhaled beyond TV
Air remaining in lungs after a maximum expiration
= residual volume (RV)
Copyright 2010, John Wiley & Sons, Inc.
Lung Capacities
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Inspiratory capacity = TV + IRV
Functional residual capacity (FRC) =
RV + ERV
Vital capacity (VC) = IRV + TV + ERV
Total lung capacity (TLC) = VC + RV
Copyright 2010, John Wiley & Sons, Inc.
Lung Capacities
Copyright 2010, John Wiley & Sons, Inc.
Respiration Step 2: Pulmonary Gas
Exchange: External Respiration

Diffusion across alveolar-capillary membrane

O2 diffuses from air (PO2 ~105 mm Hg) to
pulmonary artery (“blue”) blood (PO2 ~40 mm Hg).
(Partial pressure gradient = 65 mm Hg)
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Continues until equilibrium (PO2 ~100-105 mm Hg)
Meanwhile “blue” blood (PCO2 ~45) diffuses to
alveolar air (PCO2 ~40) (Partial pressure gradient =
5 mm Hg)
Copyright 2010, John Wiley & Sons, Inc.
Respiration Step 3: Systemic Gas Exchange:
Internal Respiration
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Occurs throughout body
O2 diffuses from blood to cells: down partial
pressure gradient
PO2 lower in cells than in blood because O2
used in cellular metabolism
Meanwhile CO2 diffuses in opposite direction:
cells  blood
Copyright 2010, John Wiley & Sons, Inc.
Internal and
External
Respiration
Copyright 2010, John Wiley & Sons, Inc.
Transport of Oxygen within Blood
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98.5% of O2 is transported bound to
hemoglobin in RBCs
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Binding depends on PO2
High PO2 in lung and lower in tissues
O2 dissolves poorly in plasma so only 1.5% is
transported in plasma
Tissue release of O2 to cells is increased by
factors present during exercise:
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High CO2 (from active muscles)
Acidity (lactic acid from active muscles)
Higher temperatures (during exercise)
Copyright 2010, John Wiley & Sons, Inc.
Transport of Carbon Dioxide
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CO2 diffuses from tissues into blood 
CO2 carried in blood:
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Some dissolved in plasma (7%)
Bound to proteins including hemoglobin (23%)
Mostly as part of bicarbonate ions (70%)
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CO2 + H2O  H+ + HCO3-
Process reverses in lungs as CO2 diffuses
from blood into alveolar air  exhaled
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Transport of
Oxygen and
Carbon Dioxide
Copyright 2010, John Wiley & Sons, Inc.
Control of Respiration
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Medullary rhythmicity area in medulla
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Quiet breathing
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Contains both inspiratory and expiratory areas
Inspiratory area  nerve signals to inspiratory
muscles for ~2 sec 
Inspiration 
Inspiration ends and muscles relax 
Expiration 
Expiratory center active only during forceful
breathing
Two areas in pons adjust length of inspiratory
stimulation
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Control of Respiration
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Control of Respiration
Copyright 2010, John Wiley & Sons, Inc.
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Regulation of Respiratory Center
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Cortical input: voluntary adjustment of
patterns
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For talking or cessation of breathing while
swimming
Chemoreceptor input will override breath-holding
Copyright 2010, John Wiley & Sons, Inc.
Regulation of Respiratory Center
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Chemoreceptor input to  increase
ventilation
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Central receptors in medulla: sensitive to  H+ or
PCO2
in CSF
Peripheral receptors in arch of aorta + common
carotids: respond to  PO2 as well as  H+ or
PCO2 in blood
Blood and brain pH can be maintained by
these negative feedback mechanisms
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Regulation of
Respiratory Center
Copyright 2010, John Wiley & Sons, Inc.
Other Regulatory Factors of Respiration
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Respiration can be stimulated by

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Sudden pain can  apnea: stop breathing
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Limbic system: anticipation of activity, emotion
Proprioception as activity is started
Increase of body temperature
Prolonged somatic pain can increase rate
Airway irritation cough or sneeze
Inflation reflex

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Bronchi wall stretch receptors inhibit inspiration
Prevents overinflation
Copyright 2010, John Wiley & Sons, Inc.
Aging and the Respiratory System

Lungs lose elasticity/ability to recoil  more
rigid; leads to
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Decrease in vital capacity
Decreased blood PO2 level
Decreased exercise capacity
Decreased macrophage activity and ciliary
action 

Increased susceptibility to pneumonia, bronchitis
and other disorders
Copyright 2010, John Wiley & Sons, Inc.