Download The Respiratory System Lecture 1 The Respiratory System The

The Respiratory System
Lecture 1
The Respiratory System
The complex of organs and tissues which are necessary to exchange
blood carbon dioxide (CO2) with air oxygen (O2) is called " respiratory
system". It consists of:
1. Conductive portion (upper respiratory tract): formed of a series of
transport passages by which air pass from the atmosphere to the
lung. It consist of (nasal cavity, nasopharynx, larynx, trachea,
bronchi, bronchioles & terminal bronchioles).
2. Respiratory portion (lower respiratory system): which is
responsible for gaseous exchange
consist of
(respiratory
bronchioles, alveolar ducts & alveoli). The alveoli are specialized
sac like structures forming the greater part of the lung & they are
the main sites for exchange of O2 & CO2 between the air & the
blood.
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The conducting portion of the respiratory system has many functions:
1. It is a system of channels through which air will reach the
lungs and to ensure adequate & continuous supply of air to
both lungs a combination of cartilages, elastic fibers,
collagen fibers & smooth muscle fibers provides the
conducting part with rigid structural support and with the
necessary flexibility and extendibility.
2. While passing through the conducting part the air will be
cleaned (by removal of foreign particles), moistened &
warmed, to carry out these functions, the mucosa of the
conducting part is lined with a specialized epithelium called
respiratory epithelium.
3. In addition the proximal part of the respiratory tract has a
specialized structures that are involved in the perception of
smell & flavor (Olfactory mucosa) & the production of
sound (Larynx).
Cartilages in the respiratory system:
Cartilages are mainly hyaline in type, found in the lamina propria, they
have various forms ranging from small plaques in the bronchi to irregular
rings & in the trachea C-shaped cartilages. The cartilages generally
produce support to the wall of the conducting part to prevent collapse of
the lumen during expiration & to ensure continuous air entry to the
lungs.
Elasic fibers in the respiratory system:
found in both conducting and respiratory parts to provide these areas with
flexibility and to allow them to return to their original shape after
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inspiration.The concentration of elastic fibers is inversely proportionate
to the diameter of the conducting tubule (ie. the smallest bronchioles have
the highest amount of elastic fibers in their lamina propria).
Smooth muscles in the respiratory system: bundles of smooth muscles
encircle the tube from the trachea to the alveolar ducts. Contraction of
those smooth muscles reduces the diameter of the conducting tubules to
regulate the air flow during inspiration and expiration.
The conducting part of the respiratory system gradually undergoes
transition into the respiratory part. The ciliated epithelium, goblet cells
& cartilages will gradually decrease in the wall of the system while the
content of smooth muscles & elastic fibers gradually increase.
Respiratory Epithelium:
Most of the conducting portion of the respiratory system is lined with
pseudostratified ciliated columnar epithelium that contains large
number of mucous secreting cells called goblet cells. As the bronchi
subdivide into bronchioles some structural changes occure are:
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The Respiratory System
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 pseudostratified epithelium will change to simple columnar
epithelium which is further reduced to simple cuboidal epithelium
in the terminal bronchioles.
 goblet cells gradually decrease in number in the smaller bronchi &
are completely absent from the epithelium in the terminal
bronchioles.

ciliated cells still present in the terminal bronchioles without the
goblet cells in order to prevent accumulation of mucous in the
respiratory portion of the system because the cilia help to move
this mucous upward toward the mouth where it is either
swallowed or expectorated.
Typical respiratory epithelium: consists of five cell types:
1. Ciliated columnar cells: most numerous type of cells, each cell
has about 300 cilia in its apical surface, called immotile cilia (due
to deficiency of the protein Dynein) those cells become shorter
with successive branching of the bronchial tree until they become
cuboidal in the most peripheral branches.
2. Mucous secreting goblet cells: the second most numerous type of
cells, they are scattered in between the ciliated columnar cells ,
their cytoplasm is filled with mucous droplets and their number
gradually decrease until they are absent in the terminal bronchioles,
they increase in some chronic respiratory diseases.
3. Basal cells: small rounded cells lie on the basement membrane,
they are not in contact with the lumen, they form stem cells from
which other cell types develop.
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4. Brush cells: columnar cells with many microvilli on their apical
surface, they have afferent nerve endings on their basal surface &
are considered to be sensory receptors.
5. Neuroendocrine cells: small rounded cells with dark nuclei &
cytoplasm filled with endocrine granules that regulate the
interaction between mucous and serous secretory functions of the
system.
In smokers the proportion of ciliated cells to goblet cells is altered so
greater number of goblet cells are found to aid in clearing the
increased amount of particulates & gaseous pollutants in their
respiratory epithelium, while the reduction in ciliated cells caused by
excessive intake of CO resulting
in decreased movement of the
mucous layer leading to congestion of the smoker’s airways.
 Nasal Cavity:
The Nasal cavity is divided into three structurally and functionally
different parts.
1. Vestibule: is the most anterior dilated part of the nasal cavity
forming the first ~1.5 cm of the conductive portion following the
nostrils which are lined with a keratinized stratified squamous
epithelium, numerous sebaceous glands & thick short hairs, within
the vestibule the epithelium loses its keratinization and undergoes
gradual transition into typical respiratory epithelium.
2. Respiratory region: at the transition from the vestibule to the
respiratory region of the nasal cavity the epithelium becomes first
non keratinized stratified squamous and then pseudostratified
ciliated columnar with goblet cells (respiratory epithelium). The
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surface of the lateral parts of the nasal cavity is thrown into folds
by bony projections called conchae. These folds increase the
surface area of the nasal cavity and they create a turbulence in the
stream of
the passing air, both functions will facilitate the
conditioning (warming, cooling and filtration) of the air. The
lamina propria contains mucous and serous glands which
supplement the secretions of the goblet cells with a large venous
plexuses known as swell bodies, they are important for
conditioning of air thus abnormal enlargement of swell bodies
with blood occurs in allergic reaction & inflammation so they
restrict air flow to the air passages.
3. olfactory region formed by tissues on the superior concha and the
nasal septum of the nasal cavity, it is lined with a special type of
epithelium called Olfactory mucosa.
Olfactory mucosa:
Is a special type of mucosa, located in the roof of the nasal cavity &
extend for a short distance down the septum and lateral wall it is
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responsible for the sensation of smell & the more sophisticated
epithelium aspect of taste. The Olfactory mucosa has a pseudostratified
columnar epithelium that is composed of three types of cells which are:
1. Basal cells: are small cone shape cells rest on the basement
membrane not in contact with the lumen their nuclei are close to
the basement membrane, these cells are regarded as the stem cells
from which new olfactory cells can develop.
2. Sustentacular cells (supporting cells): are tall cells their nuclei
are closest to the lumen & they have a narrow base in contact with
the basement membrane & microvilli on their free surface, they
give mechanical & metabolic support to the basal & olfactory cells.
3. Olfactory receptor cells: are bipolar neurons found in between
the basal & sustentacular cells they have a central bulge contain the
nucleus & from the cell extend 2 processes:
a) Dendritic process: extend to the surface epithelium where its tip
expand into a club-shaped prominence called Olfactory vesicle
which bears cilia that protrude into the nasal cavity these cilia are
sensitive to odorous substances.
b) Proximal process: very narrow & pass between the basal &
sustentacular cells to penetrate the basement membrane & join the
other proximal processes of other cells to form what is called fila
olfactoria which will then form a synaptic connection with the
olfactory bulb to form the first cranial nerve (Olfactory nerve).
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Beneath the epithelium of the olfactory mucosa the connective tissue
of the lamina propria contain small serous glands called Bowman's
glands their secretion may act as a solvent for the odorous substances,
this connective tissue is highly vascular and contain the fila olfactoria.
Paranasal sinuses:
Are closed cavities in the frontal, maxillary, ethmoid & sphenoid
bones. They are lined with thin respiratory epithelium that contains few
goblet cells. Their lamina propria contains only few small serous and
mucous glands. Those sinuses communicate with the nasal cavity through
small openings & the mucous produced in the sinuses is drained into the
nasal cavity by the action of the ciliated epithelial cells, these sinuses help
to increase the surface area for moistening & warming the inhaled air,
also the sinus cavities play a role in the nature of the sounds
produced.Sinusitis is an inflammatory process in the sinuses that may
persist for long period occur due to obstruction of the sinus openings.
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 Pharynx:
The pharynx connects the nasal cavity with the larynx. Depending on
the extent of abrasive forces on the epithelium, the pharynx is either lined
with respiratory epithelium (nasopharynx) or with a stratified squamous
epithelium (oropharynx) which also covers the surfaces of the oral cavity
and the oesophagus.Lymphocytes frequently accumulate beneath the
epithelium
of
the
pharynx.Accumulations
of
lymphoid
tissues
surrounding the openings of the digestive and respiratory passages form
the tonsils
 Larynx:
The larynx connects the pharynx and trachea. The vocal folds of the
larynx control airflow and allow the production of sound. The vocal folds
are lined by stratified squamous epithelium and contain the muscle
(striated, skeletal) and ligaments needed to control the tension of the
vocal folds.
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