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When the
respiratory
system is
mentioned,
people
generally
think of
breathing,
but
breathing is
only one of
the
activities
of the
respiratory
system. The
body cells
need a
continuous
supply of
oxygen for
the
metabolic
processes
that are
necessary to
maintain
life. The
respiratory
system works
with the
circulatory
system to
provide this
oxygen and
to remove
the waste
products of
metabolism.
It also
helps to
regulate pH
of the
blood.
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Respiration is the
sequence of events that
results in the exchange
of oxygen and carbon
dioxide between the
atmosphere and the body
cells. Every 3 to 5
seconds, nerve impulses
stimulate the breathing
process, or ventilation,
which moves air through
a series of passages
into and out of the
lungs. After this, there
is an exchange of gases
between the lungs and
the blood. This is
called external
respiration. The blood
transports the gases to
and from the tissue
cells. The exchange of
gases between the blood
and tissue cells is
internal respiration.
Finally, the cells
utilize the oxygen for
their specific
activities. This is
cellular metabolism, or
cellular respiration.
Together these
activities constitute
respiration |
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Ventilation, or breathing, is the
movement of air through the
conducting passages between the
atmosphere and the lungs. The air
moves through the passages because
of pressure gradients that are
produced by contraction of the
diaphragm and thoracic muscles.
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Pulmonary ventilation
Pulmonary ventilation is commonly referred to
as breathing. It is the process of air flowing
into the lungs during inspiration (inhalation)
and out of the lungs during expiration
(exhalation). Air flows because of pressure
differences between the atmosphere and the gases
inside the lungs.
Air, like other gases, flows from a region
with higher pressure to a region with lower
pressure. Muscular breathing movements and
recoil of elastic tissues create the changes in
pressure that result in ventilation. Pulmonary
ventilation involves three different pressures:
- Atmospheric pressure
- Intraalveolar (intrapulmonary)
pressure
- Intrapleural pressure
Atmospheric pressure is the pressure of the
air outside the body. Intraalveolar pressure is
the pressure inside the alveoli of the lungs.
Intrapleural pressure is the pressure within the
pleural cavity. These three pressures are
responsible for pulmonary ventilation.
Inspiration
Inspiration (inhalation) is the process of
taking air into the lungs. It is the active
phase of ventilation because it is the result of
muscle contraction. During inspiration, the
diaphragm contracts and the thoracic cavity
increases in volume. This decreases the
intraalveolar pressure so that air flows into
the lungs. Inspiration draws air into the lungs.
Expiration
Expiration (exhalation) is the process of
letting air out of the lungs during the
breathing cycle. During expiration, the
relaxation of the diaphragm and elastic recoil
of tissue decreases the thoracic volume and
increases the intraalveolar pressure. Expiration
pushes air out of the lungs.
Under normal
conditions, the average
adult takes 12 to 15
breaths a minute. A
breath is one complete
respiratory cycle that
consists of one
inspiration and one
expiration.
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An
instrument
called a
spirometer
is used to
measure the
volume of
air that
moves into
and out of
the lungs,
and the
process of
taking the
measurements
is called
spirometry.
Respiratory
(pulmonary)
volumes are
an important
aspect of
pulmonary
function
testing
because they
can provide
information
about the
physical
condition of
the lungs.
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Respiratory capacity
(pulmonary capacity) is
the sum of two or more
volumes.
Factors such as age,
sex, body build, and
physical conditioning
have an influence on
lung volumes and
capacities. Lungs
usually reach their
maximumin capacity in
early adulthood and
decline with age after
that. |
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The
respiratory
conducting
passages are
divided into
the upper
respiratory
tract and
the lower
respiratory
tract. The
upper
respiratory
tract
includes the
nose,
pharynx, and
larynx. The
lower
respiratory
tract
consists of
the trachea,
bronchial
tree, and
lungs. These
tracts open
to the
outside and
are lined
with mucous
membranes.
In some
regions, the
membrane has
hairs that
help filter
the air.
Other
regions may
have cilia
to propel
mucus.
Click a
menu item
listed below
to learn
more about a
component(s)
of the
conducting
passages.
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Nose and Nasal Cavities
The framework of the nose
consists of bone and cartilage.
Two small nasal bones and
extensions of the maxillae form
the bridge of the nose, which is
the bony portion. The remainder
of the framework is cartilage
and is the flexible portion.
Connective tissue and skin cover
the framework.
Air enters the nasal cavity
from the outside through two
openings, the nostrils, or
external nares. The openings
from the nasal cavity into the
pharynx are the internal nares.
Nose hairs at the entrance to
the nose trap large inhaled
particles.
Paranasal Sinuses
Paranasal sinuses are
air-filled cavities in the
frontal, maxilae, ethmoid, and
sphenoid bones. These sinuses,
which have the same names as the
bones in which they are located,
surround the nasal cavity and
open into it. They function to
reduce the weight of the skull,
to produce mucus, and to
influence voice quality by
acting as resonating chambers. |
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The pharynx, commonly called
the throat, is a passageway that
extends from the base of the
skull to the level of the sixth
cervical vertebra. It serves
both
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the respiratory and
digestive systems by
receiving air from
the nasal cavity and
air, food, and water
from the oral
cavity. Inferiorly,
it opens into the
larynx and
esophagus. The
pharynx is divided
into three regions
according to
location: the
nasopharynx, the
oropharynx, and the
laryngopharynx (hypopharynx).
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The nasopharynx is the
portion of the pharynx that is
posterior to the nasal cavity
and extends inferiorly to the
uvula. The oropharynx is the
portion of the pharynx that is
posterior to the oral cavity.
The most inferior portion of the
pharynx is the laryngopharynx
that extends from the hyoid bone
down to the lower margin of the
larynx.
The upper part of the pharynx
(throat) lets only air pass
through. Lower parts permit air,
foods, and fluids to pass.
The pharyngeal, palatine, and
lingual tonsils are located in
the pharynx. They are also
called Waldereyer's Ring.
The retromolar trigone is the
small area behind the wisdom
teeth. |
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Layrynx
The larynx, commonly called
the voice box or glottis, is the
passageway for air between the
pharynx above and the trachea
below. It extends from the
fourth to the sixth vertebral
levels. The larynx is often
divided into three sections:
sublarynx, larynx, and
supralarynx. It is formed by
nine cartilages that are
connected to each other by
muscles and ligaments.
The larynx plays an essential
role in human speech. During
sound production, the vocal
cords close together and vibrate
as air expelled from the lungs
passes between them. The false
vocal cords have no role in
sound production, but help close
off the larynx when food is
swallowed.
The thyroid cartilage is the
Adam's apple. The epiglottis
acts like a trap door to keep
food and other particles from
entering the larynx.
Trachea
The trachea, commonly called
the windpipe, is the main airway
to the lungs. It divides into
the right and left bronchi at
the level of the fifth thoracic
vertebra, channeling air to the
right or left lung.
The
hyaline
cartilage in the tracheal wall
provides support and keeps the
trachea from collapsing. The
posterior soft tissue allows for
expansion of the esophagus,
which is immediately posterior
to the trachea.
The mucous membrane that
lines the trachea is ciliated
pseudostratified columnar
epithelium similar to that in
the nasal cavity and nasopharynx.
Goblet
cells produce mucus
that traps airborne particles
and microorganisms, and the
cilia propel the mucus upward,
where it is either swallowed or
expelled. |
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Bronchi and Bronchial Tree
In the
mediastinum, at the
level of the fifth thoracic
vertebra, the trachea divides
into the right and left primary
bronchi. The bronchi branch into
smaller and smaller passageways
until they terminate in tiny air
sacs called alveoli.
The cartilage and mucous
membrane of the primary bronchi
are similar to that in the
trachea. As the branching
continues through the bronchial
tree, the amount of hyaline
cartilage in the walls decreases
until it is absent in the
smallest bronchioles. As the
cartilage decreases, the amount
of smooth muscle increases. The
mucous membrane also undergoes a
transition from ciliated
pseudostratified columnar
epithelium to simple cuboidal
epithelium to simple squamous
epithelium.
The alveolar ducts and
alveoli consist primarily of
simple squamous epithelium,
which permits rapid diffusion of
oxygen and carbon dioxide.
Exchange of gases between the
air in the lungs and the blood
in the capillaries occurs across
the walls of the alveolar ducts
and alveoli.
Lungs
The two lungs, which contain
all the components of the
bronchial tree beyond the
primary bronchi, occupy most of
the space in the thoracic
cavity. The lungs are soft and
spongy because they are mostly
air spaces surrounded by the
alveolar cells and elastic
connective tissue. They are
separated from each other by the
mediastinum, which contains the
heart. The only point of
attachment for each lung is at
the hilum, or root, on the
medial side. This is where the
bronchi, blood vessels,
lymphatics, and nerves enter the
lungs.
The right lung is shorter,
broader, and has a greater
volume than the left lung. It is
divided into three lobes and
each lobe is supplied by one of
the secondary bronchi. The left
lung is longer and narrower than
the right lung. It has an
indentation, called the cardiac
notch, on its medial surface for
the apex of the heart. The left
lung has two lobes.
Each lung is enclosed by a
double-layered serous membrane,
called the pleura. The visceral
pleura is firmly attached to the
surface of the lung. At the
hilum, the visceral pleura is
continuous with the parietal
pleura that lines the wall of
the thorax. The small space
between the visceral and
parietal pleurae is the pleural
cavity. It contains a thin film
of serous fluid that is produced
by the pleura. The fluid acts as
a lubricant to reduce friction
as the two layers slide against
each other, and it helps to hold
the two layers together as the
lungs inflate and deflate. |
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Internet Resources for Lung Cancer
