The respiratory system
• Pathway for air exchange (carbon dioxide and oxygen) made up of a few structures (nose,
pharynx, larynx, trachea, bronchi lungs)
• Additional structures such as the paranasal sinuses, pleurae, and respiratory muscles
The nose
• First part of the respiratory system responsible for smell, filtration and warming and
transporting of inhaled air
• The anterior orifices (anterior nares) lie below the cartilaginous part of the nose
• The posterior orifices (posterior nares) leading to the nasopharynx, are also known as the
choanae
• The anterior nares (nostrils) are small and oval and lead to the vestibulum, which is bounded
by the alae
• Hairs, serving as filters, are present on the inner surface of the vestibulum
• The skeleton of the external nose consists of cartilage and nasal bones superior to it
• In the midline it is supported by the nasal septum
The septum
• The septum separates the two nasal
passages from each other
• It is a vertical structure, consisting of
three parts, the perpendicular plate
(superiorly), vomer (inferiorly) and
cartilage (anteriorly)
The nasal cavities
• These cavities are irregular and have the following walls:
a. The narrow roof, which is formed by the lamina cribosa (cribiform plate) of the ethmoid
bone, lies superiorly. This plate of bone is perforated, and the olfactory nerves pass
through it
b. The floor, formed by the maxilla, palatine bones and soft palate, lies inferiorly
c. The nasal septum lies medially
Respiratory system
, d. The lateral wall is formed by the maxilla, superior and middle conchae of the ethmoid
and inferior concha (a separate bone)
• The conchae are curved bony shelves projecting from the lateral walls into the nasal cavity
• They are covered by mucosa (mucosa periosteum) and are then known as turbinates
• These turbinates enlarge the surface area covered by mucosa, thus more effectively heating,
and moistening the air
• The space of passage underneath each turbinate is called a meatus
• There are superior, middle, and inferior meati, all three leading to the nasopharynx
The mucous membrane
• This lining of the nose is
thick and richly
vascularized
• It can become distended
as a result of an allergy or
a cold
• Because it is attached to
a bone, the mucous
membrane is known as
mucoperiosteum
• The mucosa varies structurally according to the function of each area of the nose, for
example
a. The lining of the vestibulum has sweat and sebaceous glands, as well as hairs
b. The respiratory mucosa, consisting of ciliated pseudostratified columnar epithelium,
lines most of the nose and is continuous with the mucosa of the sinuses by means of
their openings and with that of the nasopharynx
c. The olfactory mucosa lines the roof and adjacent portions of the septum and lateral
walls. Nerve cells that pick up olfactory stimuli are present in this mucosa
The paranasal sinuses
• In the four large bone are arranged around the nose, air-filled cavities are found
a. Maxillary bone
b. Frontal bone
c. Ethmoid bone
d. Sphenoid bone
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,• These sinuses develop as projections from the respiratory part of the nasal cavity and are
lined with mucosa, which is a continuation of that of the nasal cavity
• At birth, they are absent or very small and enlarge at puberty
• They drain into the nasal cavity through openings at specific sites in the meati
• The function of the sinuses is to help with resonance and to make the skull lighter in weight
The maxillary sinus
• This is the largest sinus
and is contained within
the maxilla just inferior to
the orbit
• It is pyramidal in shape,
with the base (medially)
pointing towards the
lateral side of the nose
and the apex near or in the
zygoma
• The roof of this sinus
forms the floor of the orbit
• One wall faces the cheek
and the other the
infratemporal fossa
• The orifice is high up on
the medial wall and opens
into the middle meatus of
the nose
• Because this orifice lies
high up, drainage through
it is not easy and
sometimes infections
make it necessary to
create another opening lower down
• The roots of the molar and premolar teeth are present just underneath the floor of the sinus
and are sometimes covered only by the mucosa
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, The frontal sinus
• This sinus is situated in the frontal bone, immediately above the superior orbital border
• It is often asymmetrical and usually small, but may also be so large that it extends across the
entire length of the supra-orbital ridge
• It opens into the middle nasal meatus by means of a long narrow canal, the frontonasal duct
The ethmoid sinus
• The air cells of these sinuses are arranged in three groups: anterior, middle, and posterior
• They are contained in the ethmoid bone between the lateral wall of the nose and medial
wall of the orbit
• The posterior group drains into the superior meatus and the middle and anterior groups into
the middle meatus
• All these air cells are separated from the orbit by a very thin, bony wall through which
infections can easily spread
The sphenoidal sinus
• Two air cells are situated in the body of the sphenoid bone, behind the nasal passages
• The left and right air cells are usually asymmetrical
• Each opens into the spheno-ethmoidal recess above the superior concha
• (Note: the nasolacrimal duct from the lacrimal sac in the orbit opens into the inferior meatus.
The mastoid air cells are not paranasal sinuses)
The pharynx
• The pharynx is a funnel-shaped
fibromuscular tube, which forms a
common passage for air and food. It
is situated behind the nose and
mouth
• Superiorly, it is attached to the base
of the skull just behind the posterior
choanae of the nose
• Inferiorly, it extends down to the
level of the sixth cervical vertebra,
Respiratory system
