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Anatomy & Physiology (Open + Free)
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Unit 10:: The Respiratory System
Introduction to the
Respiratory Sy stem
Module 38 /
Respiratory Structures
and Functions
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Gross Anatomy and the Upper Respiratory Tract
Identify and describe gross &
m icroscopic anatom y of the
respiratory tract and related
organs.
Upper Respiratory Tract
Nose
The external portion of the nose begins at the base of the frontal bone and extends over the maxilla, with the
nasal bone providing the bridge of the nose. Extending from the nasal bone is a collection of hyaline cartilages
that make up the bulk of the nose. The medial region of the nose consists of a central septal cartilage with two
lateral processes. The tip of the nose contains the major alar cartilage. Two minor alar cartilages are found at
the sides and base of the lateral septal cartilages. Dense fibrous connective tissue is found under the skin of
the sides lateral aspects the nose, away from the cartilage. Variations in the size of a person’s nose, or its
form, are due to differences in the various cartilages.
The visible nose is actually the entryway into the nasal cavity, where the major functions of the nose occur.
The openings to the nose, the nares, are lined with coarse hairs to aid in filtration of particulate matter. The
area immediately inside the nares, the vestibule, contains a large number of sebaceous glands, sweat glands,
and hair follicles.
By The Em irr (Diagram of Nose) CC-BY-3 .0
Nose. This work by K. Larson is licensed under a Creativ e
Com m ons
Attribution
3 .0
United
States
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(http://creativ ecom m ons.org/licenses/by /3 .0/us/).
The nasal cavity is divided into right and left sides by the nasal septum. This dividing wall’s anterior portion is
made of cartilage; bone contributed by the vomer and part of the ethmoid bones of the skull make up the
posterior. The roof of the nasal cavity consists of parts of the ethmoid and sphenoid bones. Its floor, the
palate, forms the roof of the mouth. It is separated into the hard and soft palate. The anterior hard palate is
formed from the maxillary process of the palatine bone. The posterior soft palate does not contain bone and
moves during swallowing to close off the nasal cavity to prevent material from entering it from the mouth.
Extending from the nasal septum are three pairs of C-shaped structures called conchae. The superior,
middle, and inferior conchae extend the length of the nasal cavity. They are covered by a mucus membrane
that contains a large number of mucus-secreting cells and blood vessels. A bloody nose highlights the richness
of the blood supply to the membranes on the conchae. The conchae serve as baffles to increase the surface
area of the nasal cavity. The mucus glands and blood vessels aid in humidifying and warming the air coming
into the body.
There are two types of epithelial coverings in the nasal cavity: respiratory epithelium and olfactory
epithelium. Both types of epithelia appear very similar when viewed through a light microscope. The olfactory
mucosa found in the roof of the cavity detects odors. This epithelial layer contains specialized nerve cells that
detect odors and transmit impulses to the first cranial nerve. The respiratory epithelium that covers the
rest of the nasal cavity is also found through most of the respiratory tract and is pseudostratified, ciliated,
columnar epithelia.
Paranasal sinuses
Within the bones surrounding the nasal cavity are paranasal sinuses (a sinus is a hollow area), which
function to make the skull lighter as well as moisten and warm incoming air. These sinuses frequently become
filled with excess fluid when a person has a head cold. Since the paranasal sinuses serve as resonators for
speech and sound it is not surprising that the sound of the voice becomes altered when they are filled with
fluid or swollen. The frontal, sphenoid, ethmoid and maxillary bones all contain sinus cavities.
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Pharynx
As the air passes posteriorly through the nasal cavity, it enters the pharynx. This structure encompasses
three distinct areas and connects the nasal passage to the larynx in the throat. It extends about 13
centimeters or 5 inches from the base of the skull to the level of the sixth cervical vertebrae. The wall of all
three portions contains two layers of skeletal muscle. The inner layer is arranged in a circular pattern, and
the outer layer is arranged longitudinally.
Nasopharynx
The superior section of the pharynx is called the nasopharynx. It is posterior to the nasal cavity and
inferior to the sphenoid bone. This chamber shares the same epithelia as the nasal cavity and acts only as
a conduit for air. The other two portions of the pharynx contain shared passages with the digestive tract
and act as conduits for both air and food. The nasopharynx closes off during swallowing by raising the soft
palate. Also found in this area are structures associated with immune system. The paired pharyngeal
tonsils, also known as the adenoids, lie in the posterior wall of the nasopharynx.
Oropharynx
The second portion of the pharynx is the oropharynx. It runs from the soft palate to the epiglottis and is
posterior to the oral cavity. The opening from the oral cavity to the oropharynx is called the
oropharyngeal isthmus (Isthmus of Fauces). A difference between the nasopharynx and oropharynx is
the epithelial covering of the passages. In comparison to the nasopharynx, which is lined with columnar
epithelia, the oropharynx is covered by stratified squamous epithelia, that are often found covering areas
which are subject to a great deal of frictional wear. The many layers of epithelial cells serve to protect the
underlying tissues from being damaged by the food and material coming into the passage from the
mouth.
Laryngopharynx
The third portion of the pharynx is the laryngopharynx. The shortest of the three parts of the pharynx, it
runs inferiorly from epiglottis and ends superior to the esophagus. The laryngopharynx carries both air
and food and is lined with stratified sqaumous epithelia.
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Tonsils
The paired pharyngeal tonsils, also known as the adenoids, lie in the posterior wall of the nasopharynx. The
other tonsils, the tubal tonsils, protect the auditory tubes and middle ear against entering microorganism.
They are located at the opening of the tube that connects the middle ear to the nasopharynx. The auditory or
Eustachian tube equilibrates air pressures between the environment and the middle ear. The orientation of
the auditory tube changes during infancy and early childhood. The tube is oriented horizontally until around
age two. Consequently, it frequently serves as a point of entry for bacteria in children less than two years of
age. Around age two, the auditory tube changes course and slants down from the ear, allowing fluid to drain
more readily. Without the fluid to act as a growth medium and conduit to the middle ear, older children
usually experience few ear infections.
The paired palatine tonsils lie along the two sides of the Isthmus of Fauces in the oropharynx. The lingual
(lingual meaning tongue) tonsils are not in the oropharynx, but are located at the base of the tongue.
Collectively, the tonsils aid in filtering foreign material that could do harm.
Tonsils.
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Larynx
After air leaves the pharynx, it enters the larynx, a complex structure that extends from the laryngopharynx
and the hyoid bone to the trachea. It is about 5 cm (2 in.) long. In addition to providing a passageway for air,
the larynx directs air and food to their appropriate tubes. The airway is blocked by closing off the opening of
the trachea with the epiglottis upon swallowing. The vocal cords, which are used in making sound and speech,
can be found within the larynx. The epithelial lining of the larynx exhibits two different arrangements.
Initially stratified squamous epithelia lines from the laryngopharynx to the vocal cords. Inferior to the vocal
cords the epithelial lining shifts to pseudostratified, ciliated, columnar epithelia. The nine cartilage structures
found in the larynx provide key anatomical landmarks. They function to maintain an open airway. Eight of
the cartilages are composed of hyaline cartilage.
Detail of Lary nx. This work by Cenv eo is licensed under a Creativ e Com m ons Attribution 3 .0 United States
(http://creativ ecom m ons.org/licenses/by /3 .0/us/).
Epiglottis
The epiglottis is made of elastic cartilage and covered with stratified squamous epithelia. It connects
loosely to the tongue, the hyoid bone, and the rim of the thyroid cartilage. The epiglottis is normally open,
allowing air to freely flow into the rest of the larynx and the trachea. When a person swallows, the front of
the epiglottis is raised, and the posterior portion descends, covering the glottis, which is the opening to
the vocal cords and trachea. This movement directs food and water to the esophagus and prevents it
from entering the bottom portion of the larynx and the upper trachea. If someone tries to talk or laugh
and swallow at the same time, the air used to talk or laugh forces the epiglottis open, the swallowed
material “goes down the wrong tube,” and choking results.
Thyroid cartilage
The thyroid cartilage is the largest of the cartilages of the larynx and is found at the front of the larynx.
In the fetus the cartilage originates as two separate plates that fuse before birth. This roughly
triangularly shaped cartilage contains the laryngeal prominence, commonly known as the “Adam’s
apple”. The laryngeal prominence becomes more prominent in males during puberty as the larynx
widens and the voice deepens. The thyroid cartilage connects to the hyoid bone by the thyrohyoid
membrane or ligament.
Cricoid cartilage
Inferior to the thyroid cartilage is the cricoid cartilage. It connects superiorly to the thyroid cartilage by
the cricothyroid ligament and inferiorly to the trachea by the cricotracheal ligament. When an occlusion of
the upper respiratory tract occurs and a tracheostomy is performed to facilitate breathing, the
cricothyroid ligament must be punctured.
Arytenoids cartilages, cuneiform cartilages, corniculate cartilages
The next six cartilages are found in three pairs. The first pair, the arytenoids cartilages, anchor the true
vocal cords. The second pair are the cuneiform cartilages, and the third pair are the corniculate cartilages.
All three pairs of cartilages are found in the lateral and posterior walls of the larynx. Except for the
epiglottis, the arrangement of the cartilages of the larynx ensure that the passages through the larynx
remain open.
Vocal cords
Two pairs of folded tissue can be observed in the larynx immediately inferior to the epiglottis. These are
the false and true vocal cords respectively. The false vocal cords do not function in making sounds or
speech but aid in closing the glottis, which opens to the rest of the larynx and the respiratory system.
Below the false vocal cords are the true vocal cords. The true cords run from the arytenoids to the
thyroid cartilage. They are reinforced with elastic fibers and vibrate when adequate air is forced through
the gap between them, resulting in sound. Pitch control is achieved by adjusting the tension on the cords.
Lessening the tension lowers the pitch. During puberty in males the cords are usually lengthened making
for a deeper sound. Actual speech is achieved with the coordination of muscles in the pharynx, face,
tongue, soft palate, and lips.
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Upper Respiratory
By Arcadian (Head and Neck)
Open Learning Initiativ e
Unless otherwise noted this work is licensed under a Creativ e Com m ons Attribution 3 .0 Unported License.
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