The Respiratory System
Chapter 23
Introduction
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The trillions of cells making up the body
require a continuous supply of oxygen to
carry out vita functions
We can survive only a few minutes
without oxygen
As cells use oxygen, they give off carbon
dioxide a waste product of cellular
respiration
Introduction
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The major function of the respiratory system
is to supply the body with oxygen and dispose
of carbon dioxide
To achieve this function four distinct
processes, collectively called respiration occur
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–
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Pulmonary ventilation
External respiration
Transport of respiratory gases
Internal respiration
Introduction
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Pulmonary ventilation
– Air must be moved in and out of the lungs so that
the gases in the air sacs (alveoli) of the lungs are
continually changed and refreshed
– This air movement is commonly called ventilation
or breathing
Introduction
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External respiration
– Gas exchange (oxygen loading and carbon dioxide
unloading) between the blood and the air-filled
chambers of the lungs must occur
Introduction

Transport of respiratory gases
– Oxygen and carbon dioxide must be transported
between the lungs and tissue cells of the body
– This is accomplished by the cardiovascular
system, which uses blood as the transporting fluid
Introduction

Internal respiration
– At systemic capillaries, gas exchanges (oxygen
unloading and carbon dioxide loading) must be
made between the blood and tissue cells
Respiratory System
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The organs of the
respiratory system
include the nasal
cavity, pharynx,
larynx, trachea,
bronchi, lungs
Respiratory System
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Functionally, the respiratory system
consists of the respiratory and the
conducting zones
– The respiratory zone, the actual site of gas
exchange, is composed of the respiratory
bronchioles, alveolar ducts, and alveoli
– The conducting zone includes all other
respiratory passageways, which provide
fairly rigid conduits for air to reach the sites
of gas exchange
– Organs of the conducting zone clean, warm
and humidify the incoming air
The Nose
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The nose is the
only visible part of
the respiratory
system
The external
framework of the
nose
The Nose
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The functions of the nose include
– Providing an airway for respiration
– Moistening and warming entering air
– Filtering inspired air and cleansing it of
foreign matter
– Serving as a resonating chamber for speech
– Housing the olfactory receptors
The Nose
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The structures of
the nose are divided
into the
– External nose
– Nasal cavity
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Surface features
–
–
–
–
–
–
–
Root (between eyes)
Bridge
Dorsum nasi
Apex
Philtrum
External nares
Alae
The Nose
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The nasal cavity lies in and posterior to the
external nose
During breathing air enters the external
cavity by passing through the external
nares or nostrils
The nasal cavity is divided by a midline
nasal septum
The nasal cavity is continuous posteriorly
with the nasal portion of the pharynx
through the internal nares
The Nose
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The roof of the nasal cavity is formed by
the ethmoid and sphenoid bones of the
skull
The floor is formed by the palate which
separates it from the oral cavity below
Anteriorly, where the palate is supported
by the maxillary processes and the palatine
bones is considered the hard palate
The unsupported posterior portion is the
muscular soft palate
The Nose
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The vestibule is lined with skin containing
sebaceous and sweat glands and numerous hair
follicles
The hair or vibrissae filter coarse particles
from inspired air
The Nose
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The nasal cavity is lined with two types of
mucous membrane
The olfactory mucosa, lining the slitlike
superior region of the nasal cavity, contain
the receptors for the sense of smell
The balance of the nasal cavity is lined with
respiratory mucosa which is made up of
pseudostratified columnar epithelium,
containing scattered goblet cells, that rests
on a lamina propria richly supplied with
mucous and serous glands
The Nose
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Each day the mucous glands secrete about
a quart of sticky mucous containing
lysozyme, an antibacterial enzyme
The mucous traps inspired dust, bacteria
and other debris, while lysozyme attacks
and destroys bacteria chemically
The epithelial cells of the respiratory
mucosa also secrete defensins, natural
antibotics that help to get rid of invading
microbes
The Nose
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The ciliated cells of the respiratory
mucosa create a gentle current that
moves the sheet of contaminated mucus
posteriorly toward the throat where it is
swallowed and digested by stomach juices
These ciliated cells become sluggish in
cold weather allowing mucus to
accumulate in the nasal cavity where it
“runs” on a cold day
The Nose
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A rich plexus of thin walled veins
underlies the nasal epithelium and warms
the incoming air as it flows across the
mucosal surface
Blood flow increases when the weather
turns cold
Because of its superficial location and the
extent of vessels, nosebleeds are common
and often profuse
The Nose
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Protruding medially
from each lateral
wall of the nasal
cavity are three
mucosa-covered
projections, the
superior, middle and
inferior conchae
The conchae serve to
increase nasal
turbulence in the
nasal cavity
Mucus/sneeze
The Paranasal Sinuses
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The nasal cavity is
surround by sinuses
located in the
frontal, sphenoid,
ethmoid and
maxillary bones
They function to
–
–
–
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Produce mucus
Lighten the skull
Warm the air
Voice resonance
The Pharynx
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The funnel shaped pharynx (throat)
connects the nasal cavity and mouth to
the larynx and esophagus inferiorly
It serves as a common pathway for food
and air
The pharynx extends for about 5 inches
from the base of the skull to the level of
the sixth cervical vertebrae
Its three regions are nasopharynx,
oropharynx and laryngopharynx
The Nasopharynx
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The nasopharynx lies
above the point of
food entry, it serves
only as an air
passageway
During swallowing
the uvula reflects
posteriorly to close
off the nasopharynx
and prevent food
from entering the
nasal cavity
The Nasopharynx
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The nasopharynx is
continuous with the
nasal cavity through
the internal nares
It ciliated pseudostratified epithelium
produces mucus
Mucosa high on the
posterior wall
contains masses of
lymphatic tissue, the
pharyngeal tonsils or
adenoids
The Oropharynx
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The oropharynx lies
posterior to the oral
cavity and is
continuous with it
through an archway
called the fauces
Both swallowed food
and air pass through
Lined with stratified
squamous epithelium
for protection from
food abrasion and
chemical trauma
The Oropharynx
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Three tonsils lie
embedded in the
oropharyngeal
mucosa
– Paired palatine
tonsils
– Lingual tonsil
The Laryngopharynx
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The laryngopharynx
serves as a common
pathway for food and
air and is lined with
stratified squamous
epithelium
It lies directly
posterior to the
upright epiglottis and
extends to the larynx
where the digestive
and respiratory
pathways diverge
The Laryngopharynx
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The esophagus
conducts food to the
stomach while air
enters the larynx
anteriorly
During swallowing
food has the “right of
way” and air passage
temporarily stops
The Larynx
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The larynx attaches
to the hyoid bone
superiorly and
opens into the
laryngopharynx
Inferiorly is is
continuous with the
trachea
The Larynx
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The larynx has three important functions
– It provides an airway for respiration
– Act as a switching mechanism to route air
and food into the proper channels
– Vocal cords housed in larynx are used in
voice production
The Larynx
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The framework of
the larynx is an
arrangement of nine
cartilages connected
by membranes and
ligaments
Except for the
epiglottis, all
laryngeal cartilages
are made of hyaline
The Larynx
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The large, shield
shaped thyroid
cartilage is formed
by the fusion of two
cartilage plates
The laryngeal
prominence marks
the midline fusion
point
The cricoid cartilage
is anchored to the
trachea inferiorly
The Larynx
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Three pairs of
small cartilages,
the arytenoid,
cuneiform and
corniculate form
part of the lateral
and posterior walls
of the larynx
The arytenoid
anchors the vocal
cords
The Larynx
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The ninth cartilage
the flexible, spoon
shaped epiglottis is
composed of elastic
cartilage
It is almost entirely
covered by mucosa
The epiglottis
extends from the
posterior aspect of
the tongue to its
anchoring point on
the thyroid cartilage
The Larynx
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When only air is
flowing into the
larynx, the inlet to
the larynx is open
wide and the free
edge of the epiglottis
projects upward
During swallowing
the larynx is pulled
superiorly and the
epiglottis tips to
cover the laryngeal
inlet
The Vocal Folds
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The vocal ligaments
attach the arytenoid
and thyroid
cartilages
These ligaments are
composed of elastic
fibers
The vocal cords
vibrate, producing
sound as air rushes
up from lungs
The Vocal Folds
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The opening
through which air
passes is the glottis
Superior to the
vocal cords are the
vestibular cords
which play no part
in voice production
Vocal Folds
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Stratified squamous epithelium lines the
superior portion of the larynx, an area
subject to food contact
Below the vocal folds the epithelium is
pseudostratified ciliated columnar
epithelium
Cilia move the mucus away from our
lungs
Voice Production
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Speech involves the intermittent release
of expired air and opening and closing of
the glottis
The length of the true vocal cords and the
size of the glottis are altered by the action
of the intrinsic laryngeal muscles most of
which move the arytenoid cartilages
As the length and tension of the vocal
folds change, the pitch of the sound is
altered
Voice Production
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The glottis is wide when we produce deep
tones and narrows to a slit for high
pitched sounds
Length and thickness of the vocal folds
changes for males during puberty
Loudness of the voice depends on the
force with which the airstream rushes
across the vocal cords
The greater the force, the stronger the
vibration and the louder the sound
Sphincter Functions of Larynx
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The vestibular folds can perform a
sphincter function under certain conditions
In abdominal straining associated with
defecation and urination, inhaled air is
held temporarily in the lower respiratory
tract by closing the epiglottis
The abdominal muscle then contract and
the interabdominal pressure rises
The action know as the Valsalva manuever
can also stabilize the trunk when one lifts a
heavy load
The Trachea
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The trachea
descends from the
larynx through the
neck and into the
mediastinum
It ends by dividing
into the two
primary bronchi at
midthorax
10 cm long and
2.5 cm in diameter
The trachea is very
flexible and mobile
The Tracheal Wall
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The tracheal wall consists of several layers that are
common in many tubular organs of the body
The Tracheal Wall
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From internal to external these layers are the mucosa,
submucosa, and adventitia
The Tracheal Wall
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The mucosa contains the same goblet cells containing
pseudostratifed epithelium that occurs throughout
most the of respiratory tract
The Tracheal Wall
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Its cilia continually propel mucus, loaded with dust
particles and other debris, toward the larynx
The Tracheal Wall
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Smoking inhibits and ultimately destroys
the cilia in the mucosa layer
When their function is lost, coughing is
the only means of preventing mucus from
accumulating in the lungs
Smokers with respiratory congestion
should avoid medications that inhibit the
cough reflex
The Tracheal Wall
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The submucosa, a connective tissue layer, contains
seromucous glands that help produce the mucus
“sheets” within the trachea
The Tracheal Wall
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The adventitia is a connective tissue layer that is
reinforced by 16 to 20 C-shaped rings of hyaline
cartilage
The Tracheal Wall
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The cartilage rings prevent the trachea from
collapsing and keep the airway open despite the
changes in pressure that occur in breathing
The Tracheal Wall
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The open posterior parts of the rings, which abut the
esophagus are connected by smooth muscle fibers of
the trachealis muscle and soft connective tissue
The Tracheal Wall
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Since this portion of the tracheal wall is not rigid, the
esophagus can expand anteriorly as swallowed food
passes through it
The Trachea
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The last tracheal
cartilage is
expanded and a
spar of cartilage
called the carina
projects posteriorly
from its inner
surface, marking
the point where the
trachea splits
Contacting this
point results in
violent coughing
The Trachea
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Tracheal obstruction is life threatening
The Heimlich maneuver was developed to
expel an obstruction using the residual
air in the victim’s lungs
The maneuver creates interthoracic
pressure that drives the obstruction from
its lodging point
The Conducting Zone
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The right and left primary bronchi are formed by the
division of the trachea at the level of T5
The Conducting Zone
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Each bronchi runs obliquely in the mediastinum
before plunging into the medial depression (hilus) of
the lung on each side
Conducting Zone: Bronchial Tree
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Once inside the lungs, each primary bronchus subdivides into secondary and then tertiary bronchi
which then divide further (23 orders of branching)
The Conducting Zone
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Air passages under 1mm in diameter are called
bronchioles and the smallest of these are called
terminal bronchioles and are less than 0.5mm
The Conducting Zone
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The tissue composition of the walls of the
primary bronchi mimics that of the trachea
but as the conducting tubes become smaller, a
number of structural changes occurs
– The cartilage supports change
• Rings are replaced by plates and then none at all
– The epithelium type changes
• Pseudostratified columnar, to columnar, to cuboidal
• Debris removed by macrophages at bronchiole level
– The amount of smooth muscle increases
• A complete layer of circular smooth muscle allows for
vasoconstriction and vasodilation
The Respiratory Zone
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The respiratory zone begins as the terminal bronchioles
feed into respiratory bronchioles within the lungs
Protruding from these smallest bronchioles are scattered
alveoli
The Respiratory Zone
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The respiratory bronchioles lead into alveolar ducts
The ducts lead into terminal clusters of alveoli called
alveolar sacs
Respiration takes place within the alveoli
The Respiratory Membrane
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The walls of the
alveoli are composed
primarily of a single
cell layer of
squamous epithelial
cells, called Type I
cells underlain by a
flimsy basal lamina
The cell walls are
extremely thin to
allow for ease of gas
exchange
The Respiratory Membrane
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The external surfaces
of the alveoli are
densely covered with a
web of pulmonary
capillaries
Together the alveolar
and capillary walls
and their fused basal
lamina form the
respiratory membrane
with gas on one side
and blood on the other
The Respiratory Membrane
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Gas exchange occurs
by simple diffusion
across the respiratory
membrane
Oxygen from the
alveoli passes into the
blood and carbon
dioxide leaves the
blood to enter the
alveoli
The Respiratory Membrane
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Scattered amid the
type I squamous cells
that form the alveoli
walls are cuboidal
type II cells
Type II cells secrete a
fluid containing a
surfactant that coats
the alveolar surfaces
which reduces the
surface tension of the
alveolar fluid
Type II Cell
The Respiratory Membrane
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Lung alveoli have
three other features
– Surrounded by fine
elastic fibers
– Open pores connect
adjacent alveoli
• Allow for pressure
equalization
• Alternative air routes
for blocked bronchi
– Alveolar macrophages
crawl freely along the
internal alveolar
surfaces
Pores
The Lung
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The lungs occupy all of the thoracic cavity except the
mediastinum
Each cone shaped lung is suspended in its own pleural
cavity and connected to the mediastinum
The Lung
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The anterior, lateral and posterior lung surfaces lie in
close contact with the ribs and forms a curving surface
called the costal surface
The apex is the superior tip of the lung
The Lung
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The concave inferior surface that rests on the
diaphragm is called the base
The hilus is the location where the pulmonary and
systemic circulation and the primary bronchi enter
The Lung
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The left lung is divided
into two lobes (upper
and lower) while the
right has three lobes
(upper, middle, lower)
Each of the lobes
contains a number of
bronchopulmonary
segments separated by
connective tissue
Each lung has 10
segment
The Pluera
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The pleura is a thin,
double layered serosa
The parietal pleura
lines the thoracic wall
and superior surface
of the diaphragm
The visceral pleura
covers the external
surface of the lung
The pleura produce
the fluid that lubricate
the membrane
End of Material
Chapter 23