The Respiratory System
Chapter 21
Introduction



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 which the body must
eliminate
Introduction


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
–
–
–
–
Pulmonary ventilation
External respiration
Transport of respiratory gases
Internal respiration (cellular respiration)
Introduction

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

External respiration
– Gas exchange (oxygen loading and carbon dioxide
unloading) must occur between the blood and the
air-filled alveoli of the lungs
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 the systemic capillaries, gas exchanges (oxygen
unloading and carbon dioxide loading) must be
made between the blood and tissue cells
Respiratory System

The organs of the
respiratory system
include the nose,
nasal cavity,
paranasal sinuses
pharynx, larynx,
trachea, bronchi,
and the lungs
which contain the
terminal air sacs or
alveoli
Respiratory System



Functionally, the
respiratory
structures are
divided into
respiratory and
conducting zones
Visible structures
represent the
conducting zone
Respiratory zone
structures are
small and lie deep
within the lungs
Respiratory System

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
Respiratory System


Organs of the conducting zone clean,
warm and humidify the incoming air
Thus, the air reaching the lungs contain
must less dust than what entered the nose
and is warm and damp
The Nose


The nose is the
only externally
visible part of the
respiratory system
The external
framework of the
nose
The Nose

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 (smell) receptors
The Nose

The structures of
the nose are divided
into the
– External nose
– Nasal cavity

Surface features
–
–
–
–
–
–
–
Root (between eyes)
Bridge
Dorsum nasi
Apex
Philtrum
External nares
Alae
The Nose - Nasal Cavity
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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 - Nasal Cavity




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 - Nasal Cavity


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 - Nasal Cavity

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
The Nose - Respiratory Mucosa
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

The respiratory mucosa is made up of
pseudostratified columnar epithelium,
containing scattered goblet cells, that
rests on a lamina propria
This lamina propria is richly supplied
with compound tubuloalveolar glands
that contain mucous and serous cells
Mucous cells secrete mucus, whereas
serous cells in glands secrete a watery
fluid containing digestive enzymes
The Nose - Respiratory Mucosa



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 - Respiratory Mucosa


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 when you come
inside
The Nose - Respiratory Mucosa



The nasal mucosa is richly supplied with
sensory nerve endings
A sneeze reflex is stimulated when
irritating particles (dust, pollen) contact
this sensitive mucosa
The sneezing propels air outward in a
violent burst, expelling the irritant from
the nose
The Nose - Respiratory Mucosa



A rich plexus of thin walled capillaries
underlies the lamina propria of the nasal
mucosa and warms the incoming air as it
flows across the mucosal surface
Blood flow increases when the
temperature decreases
Because of its superficial location and the
extent of vessels, nosebleeds are common
and often profuse
The Nose - Nasal Conchae

Protruding medially
from each lateral
wall of the nasal
cavity are three
mucosa-covered
projections, the
superior, middle of
the ethmoid bone
and inferior conchae
which is a separate
bone
The Nose - Nasal Conchae



The groove inferior
to each concha is a
meatus
As inhaled air moves
over the concha the
turbulance created
increases the amount
of contact between
the nasal mucosa and
this inspired air
This acts to trap
particulates in mucus
The Nose - Nasal Conchae


The conchae and nasal mucosa not only
function during inhalation to filter, heat,
and moisten air, but also act during
exhalation to reclaim this heat and
moisture
This reclamation mechanism minimizes
the amount of moisture and heat lost
from the body through breathing, helping
us to survive in dry and cold climates
The Nose - Paranasal Sinuses


The nasal cavity is
surround by sinuses
located in the
frontal, sphenoid,
ethmoid and
maxillary bones
They function to
–
–
–
–
Produce mucus
Lighten the skull
Warm the air
Voice resonance
The Pharynx


The pharynx is
the funnel shaped
passage way than
connects the nasal
cavity and mouth
superiorly to the
larynx and the
esophagus
inferiorly
Nasopharynx,
oropharynx,
laryngopharynx
The Pharynx



The pharynx 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
In the context of the digestive tract, the
pharynx is commonly called the throat
The Pharynx


On the basis of location and function, the
pharynx is divided into nasopharynx,
oropharynx, laryngopharynx
The muscular wall of the pharynx
consists of skeletal muscle throughout its
length, but the nature of the mucosal
lining varies among the three pharyngeal
regions
The Nasopharynx


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



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



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

Two tonsils lie
embedded in the
oropharyngeal
mucosa
– Paired palatine
tonsils
– Lingual tonsil
(posterior surface of
the tongue)
The Laryngopharynx


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


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


The larynx attaches
to the hyoid bone
superiorly and
opens into the
laryngopharynx
Inferiorly is is
continuous with the
trachea
The Larynx

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


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



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


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



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


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



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


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



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



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




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
Innervation of the Larynx


The larynx receives its sensory and motor
innervation through the superior
laryngeal branch of each vagus nerve and
from the recurrent laryngeal nerves,
which branch off the vagus in the
superior thorax and loop superiorly to
ascend through the neck
The backtracking course these nerves is
unusual
The Trachea




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

The tracheal wall consists of several layers that are
common in many tubular organs of the body
The Tracheal Wall

From internal to external these layers are the mucosa,
submucosa, and adventitia
The Tracheal Wall

The mucosa contains the same goblet cells containing
pseudostratifed epithelium that occurs throughout
most the of respiratory tract
The Tracheal Wall

Its cilia continually propel mucus, loaded with dust
particles and other debris, toward the larynx
The Tracheal Wall



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

The submucosa, a connective tissue layer, contains
seromucous glands that help produce the mucus
“sheets” within the trachea
The Tracheal Wall

The adventitia is a connective tissue layer that is
reinforced by 16 to 20 C-shaped rings of hyaline
cartilage
The Tracheal Wall

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

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

Since this portion of the tracheal wall is not rigid, the
esophagus can expand anteriorly as swallowed food
passes through it
The Trachea


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

The right and left main (primary) bronchi are the
largest conduits in the bronchial tree
The Conducting Zone

The right and left primary bronchi are formed by the
division of the trachea at the level of T4 (T7 living)
The Conducting Zone

Each bronchi runs obliquely in the mediastinum
before plunging into the medial depression (hilus) of
the lung on each side
Conducting Zone: Bronchial Tree

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

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

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


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 Zone



About 300 million air-filled alveoli crowd
together within the lungs, accounting for
most of the lung volume
All these cells provide for a tremendous
surface area for gas exchange
The total area of all alveoli in an average
pair of lungs is 140 square meters, or
1500 square feet, which is 40 times
greater than the surface of the skin
The Respiratory Zone

The wall of each alveolus consists of a single
layer of squamous epithelial cells called Type I
cells surrounded by a delicate lamina
The Respiratory Membrane


The cell walls are
extremely thin to
allow for ease of gas
exchange
The wall is 15 times
thinner than a piece
of paper
The Respiratory Membrane


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


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


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 prevents the
walls from sticking
during exhalation
The Respiratory Membrane

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
The Respiratory Membrane



Alveolar macrophages (dust cells) which
actually live in the air space and remove
the tiniest inhaled particles not trapped
by the mucus
Most dust filled macrophages migrate
from the alveoli to the broncholes where
ciliary action carries them into the
pharynx to be swallowed
By this mechanism over 2 million dust
cells are cleared each hour!
The Pleurae


Around each lung is
a flattened doulbe
layered sac whose
walls form a serous
membrane called
the pleurae
There is an outer
parietal pleura and
an inner visceral
pleura
The Pleurae


The parietal pleura
covers the internal
surface of the
thoracic wall, the
superior surface of
the diaphragm and
the lateral surfaces
of the mediastinum
It also enclosed the
great vessels
running to the lung
root
The Pleurae

In the area of the
lung root the
membrane reflects
inward forming the
visceral pleura
which covers the
entire external lung
surface
The Pleurae


The pleural cavity is
the space between
the parietal and
visceral pleurae
It is actually a slit
like space filled with
a layer of pleural
fluid
The Pleurae


Secreted by the pleurae, this lubricating
fluid allows the lungs to glide without
friction over the thoracic wall during
breathing movements
The fluid also holds the parietal and
visceral pleurae together, just as a film of
oil or would hold two glass plates
together
The Pleurae


The two pleurae can easily slide from side
to side across each other, but their
separation is strongly resisted by the
surface tension of the fluid between the
membranes
Consequently, the lungs cling tightly to
the thoracic wall and are forced to
expand and recoil as the volume of the
thoracic cavity increases and decreases
during breathing
The Pleurae

The pleurae also
help divide the
thoracic cavity into
three separate
compartments
– Central
mediastinum with
the heart
– Two lateral pleurae
each containing a
lung
The Pleurae


The compartments
prevent the moving
lungs or heart from
interfering with one
another
The compartments
also limit the spread
of local infections
and the extent of
traumatic injury
The Lungs


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 Lungs


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 Lungs


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 Lungs



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
similar segments
The Lungs

The bronchopulmonary segments have
clinical significance in that they limit the
spread of some diseases within the lung,
because infections do not easily cross the
connective tissue partitions between them
The Lungs

Furthermore,
because only small
veins span these
partitions,
surgeons can
neatly remove
segments without
cutting any major
blood vessel
The Lungs



The smallest sub division of the lung is
the lobule
Appearing on the lung surface as
hexagons ranging in size from the size of
a pencil eraser to the size of a penny each
lobule is served by a large bronchiole
In most city dwellers and in smokers the
connective tissue that separates
individual lobules is blackened with
carbon
The Lungs




The lungs consist largely of air tubes and
spaces
The balance of the tissue, its stroma, is a
framework of connective tissue
containing many elastic fibers
As a result the lungs are light, soft,
spongy, elastic organs that weigh only
1.25 pounds
The elasticity helps to reduce the effort
required for breathing
Blood Supply / Nerves of the Lungs


The pulmonary arteries deliver oxygen poor
blood to the lungs for oxygenation
In the lung, these arteries branch along the
bronchial tree
Blood Supply / Nerves of the Lungs



Generally, the arteries lie posterior to the
corresponding bronchi
The smallest arteries feed into the
pulmonary capillary network around the
alveoli
Oxygenated blood is carried from the
alveoli of the lungs back to the heart by the
pulmonary veins, whose tributaries
generally lie anterior to the corresponding
bronchi within the lungs
Blood Supply / Nerves of the Lungs


The lungs are innervated by sympathetic,
parasympathetic, and visceral sensory
fibers that enter each lung through the
pulmonary plexus on the lung root
Parasympathetic fibers constrict the air
tubules whereas the sympathetic fibers
dilate them
Ventilation

Breathing or pulmonary ventilation
consists of two phases
– Inspiration is the period when air flows into
the lungs
– Expiration is the period when gases exit the
lungs
Inspiration



During inspiration the lungs increase in
volume by enlarging in all dimensions
Inspiration lowers the air pressure within
the lungs
Air flows from areas of high pressure to
areas of low pressure to equalize the
pressure within the lung to that outside
the lung
Inspiration

During normal quiet inspiration, the
diaphragm and external intercostal
muscles produce the muscle movement
Inspiration


When the dome
shaped diaphragm
contracts, it moves
inferiorly and
flattens
As a result the
vertical dimension
of the thoracic
cavity increases
Inspiration


The external intercostal muscles
contract to raise the
ribs
Because the ribs
normally extend
anterioinferiorly
from the vertebral
column, lifting them
enlarges both the
lateral and anterior
dimensions
Inspiration

Although these
actions expand the
thoracic dimensions
by only a few
millimeters along
each plane, this
movement is
sufficient to
increase thoracic
cavity volume by
almost a pint which
is equal to normal
resting inspiration
Inspiration


During deep or
forced inspiration,
additional muscles
contract and further
increase thoracic
volume
The rib cage is
elevated by the
scalenes and sternocleidomastoid in the
neck and the
pectoralis minor
Expiration


Quiet expiration in
healthy people is a
passive process
As the respiratory
muscles relax, the
rib cage drops
under the force of
gravity and the
relaxing diaphragm
moves superiorly
Expiration


At the same time,
the many elastic
fibers with the
lungs recoil
The result is that
the volume of the
thorax and lungs
decrease
simultaneously,
which pushes air
from the lungs
Expiration


Forced expiration is an active process
produced by the contraction of muscles in
the abdominal wall, primarily the oblique
and transverse abdominis muscles
These contractions
– Increase the interabdominal pressure which
forces the diaphragm superiorly
– Sharply depresses the rib cage and thus
decreases thoracic volume
Expiration

The internal intercostal muscles,
quadratus lumborum, and the latissimus
dorsi also help to depress the rib cage
End of Material
Chapter 21