Respiratory System Notes
Lecture 1
Video 1: Nasal cavi8es
1.The main func.on of the respiratory system is the intake of oxygen and the removal of
CO2. Oxygen is used to break down glucose in a process called cellular respira8on, which
produces chemical energy in the form of ATP and CO2.
The respiratory system is also involved in controlling the blood Ph.
Respiratory organs entrap incoming air par.cles, control temperature and water (H2O)
content in the air, produce vocal sounds, and are essen.al for the sense of smell.
2. Now let’s focus on the upper respiratory system, also known as upper airway.
In order to understand the anatomy of the upper respiratory system, we have to
conceptualise the skull as a collec.on of compartments or cavi.es where the nasal cavi.es
are.
The nasal cavi8es are between the orbits. They have walls, floors, and ceilings, which are
predominantly composed of bone and car.lage. The anterior openings to the nasal cavi.es
are nares (nostrils), and the posterior openings are choanae (posterior nasal apertures).
Con.nuous with the nasal cavi.es are air-filled extensions (paranasal sinuses), which project
laterally, superiorly, and posteriorly into surrounding bones. The largest, the maxillary
sinuses, are inferior to the orbits.
The oral cavity is inferior to the nasal cavi.es, and it is separated from them by the hard and
so* palates. The floor of the oral cavity is formed en.rely of soN .ssues.
The anterior opening to the oral cavity is the oral fissure (mouth), and the posterior opening
is the oropharyngeal isthmus. Unlike the nares and choanae, which are con.nuously open,
both the oral fissure and oropharyngeal isthmus can be opened and closed by surrounding
soN .ssues.
The two nasal cavi.es are the uppermost parts of the respiratory tract and contain the
olfactory receptors. They are elongated wedge-shaped spaces with a large inferior base and
a narrow superior apex and are held open by a skeletal framework consis.ng mainly of bone
and car.lage.
3. The only externally visible part of the respiratory system is the nose, which is the primary
passageway for incoming air. It has a variety of respiratory func.ons, condi.oning incoming
air, filtering and cleaning the air, func.oning as a resona.ng chamber for speaking, and
containing the smell or olfactory receptors. The condi.oning of incoming air consists of
moistening and warming.
The paired external nares, commonly known as nostrils, open into the nasal cavity. The
nasal ves8bule is a space inside the flexible nasal .ssues. Its epithelium has coarse hairs
extending across the external nares. Large par.cles in the air, including dust, sand, and
insects, become trapped in these hairs, preven.ng them from entering the nasal cavity.
4. Each nasal cavity has a floor, roof, medial wall, and lateral wall. Those walls are covered
with epithelium.
Floor. The floor of each nasal cavity is smooth, concave, and the naris opens anteriorly into
the floor. It consists of:
SoN .ssues of the external nose, and
The upper surface of the pala8ne process of the maxilla and the horizontal plate of
the pala8ne bone, which together form the hard palate.
Medial wall. The medial wall of each nasal cavity is oriented ver.cally in the median sagiWal
plane and separates the right and leN nasal cavi.es from each other.
The nasal septum consists of:
• The septal nasal car8lage anteriorly,
• Posteriorly, mainly the vomer and the perpendicular plate of the ethmoid bone,
Lateral wall. The lateral wall is characterized by three curved shelves of bone (conchae),
which are one above the other and project medially and inferiorly across the nasal cavity.
The medial, anterior, and posterior margins of the conchae are free.
The conchae divide each nasal cavity into four air channels:
• An inferior nasal meatus between the inferior concha and the nasal floor.
• A middle nasal meatus between the inferior and middle concha.
• A superior nasal meatus between the middle and superior concha.
• A spheno-ethmoidal recess between the superior concha and the nasal roof.
These conchae increase the surface area of contact between .ssues of the lateral wall and
the respired air.
The openings of the paranasal sinuses, which are extensions of the nasal cavity that erode
into the surrounding bones during childhood and early adulthood, are on the lateral wall
and roof of the nasal cavi.es. In addi.on, the lateral wall also contains the opening of the
nasolacrimal duct, which drains tears from the eye into the nasal cavity.
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5. Each nasal cavity consists of three general regions—the nasal ves.bule, the respiratory
region, and the olfactory region.
• The nasal ves8bule is a small dilated space just internal to the naris that is lined by
skin and contains hair follicles.
• The respiratory region is the largest part of the nasal cavity, has a rich neurovascular
supply, and is lined by respiratory epithelium composed mainly of ciliated and
mucous cells.
• The olfactory region is small, is at the apex of each nasal cavity, is lined by olfactory
epithelium, and contains the olfactory receptors.
The nasal cavi.es adjust the temperature and humidity of respired air by the ac.on of a rich
blood supply, and trap and remove par.culate maWer from the airway by filtering the air
through hair in the ves.bule and by capturing foreign material in abundant mucus.
Respiratory epithelium which is characterised by pseudostra.fied ciliated columnar
epithelium with a thick basement membrane. The key cells of this .ssue are:
• Ciliated columnar cells sweeping the mucus along the surface,
• Goblet cells secre.ng mucus, the only unicellular exocrine gland in human
characterised by a basal nuclei and apical domains filled with granules of
glycoproteins.
• Brush cells, which act as chemosensory cells.
• Basal stem cells.
6. Paranasal sinuses are a ring of air-filled spaces inside the skull bones that open into the
nasal cavity and are lined with respiratory epithelium which is con.nuous with the lining of
the nasal cavity
Those sinuses reduce the skull’s weight and resonate, affected the quality of the voice. They
also help to warm and moisten the incoming air. Mucus produced by the paranasal
eventually flows to the nasal cavity.
There are four paranasal air sinuses—the ethmoidal cells, and the sphenoidal, maxillary,
and frontal sinuses. Each is named according to the bone in which it is found.
Video 2: Pharynx
1. The pharynx, commonly called the throat, is a musculofascial half-cylinder that is
posterior to the nasal, oral, and laryngeal cavi.es, and links the oral and nasal cavi8es in the
head to the larynx and oesophagus in the neck. The pharyngeal cavity is a common pathway
for air and food.
The pharynx extends from the cranial base to the inferior border of the cricoid car8lage
anteriorly and the inferior border of C6 vertebra posteriorly. The pharynx is widest opposite
the hyoid bone and narrowest at its inferior end, where it is con.nuous with the
oesophagus.
2 The pharynx is a musculofascial half-cylinder. The nasopharynx is behind the posterior
apertures (choanae) of the nasal cavi.es and above the level of the soJ palate. Its ceiling is
formed by the sloping base of the skull and consists of the anterior part of the body of the
sphenoid bone and the basal part of the occipital bone.
The posterior wall of the pharynx is separated from the posteriorly posi.oned vertebral
column by a thin retropharyngeal space containing loose connec.ve .ssue.
The ceiling and lateral walls of the nasopharynx form a domed vault at the top of the
pharyngeal cavity that is always open. The most prominent features on each lateral wall of
the nasopharynx are:
The pharyngotympanic tubes open into the lateral walls of the nasopharynx. This is located
posterior to and slightly above the level of the hard palate, and lateral to the top of the soN
palate. Because the pharyngotympanic tube projects into the nasopharynx from a
posterolateral direc.on, its posterior rim forms an eleva.on or bulge on the pharyngeal wall.
Posterior to this tubal eleva.on (torus tubarius) is a deep recess (pharyngeal recess).
There is a large collec.on of lymphoid .ssue (the pharyngeal tonsil) in the mucosa covering
the roof of the nasopharynx. Enlargement of this tonsil, known then as adenoids, can
occlude the nasopharynx so that breathing is only possible through the oral cavity
The laryngopharynx extends from the superior margin of the epiglo_s to the top of the
oesophagus at the level of vertebra Cervical VI (sixth)
The laryngeal inlet opens into the anterior wall of the laryngopharynx. Inferior to the
laryngeal inlet, the anterior wall consists of the posterior aspect of the larynx.