The document summarizes the development of the respiratory system. It describes how the nasal cavities, larynx, trachea, bronchi and lungs develop from the foregut endoderm and surrounding mesoderm between 4-8 weeks of gestation. It also discusses the maturation of the lungs into alveoli after birth and anomalies that can occur during respiratory development.

1. Development of Respiratory system
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2. DEVELOPMENT OF THE NASAL CAVITIES
• At 4th week as the face
develops, the nasal placodes
become depressed, forming
nasal pits.
• Proliferation of the
surrounding mesenchyme
forms the medial and
lateral nasal prominences,
which results in deepening
of the nasal pits and
formation of primordial
nasal sacs.
• Each nasal sac grows
dorsally, ventral to the
developing forebrain.
• .
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• At first, the nasal sacs are separated from the oral cavity by the
oronasal membrane.
•This membrane ruptures by the end of the sixth week, bringing the
nasal and oral cavities into communication.
•Temporary epithelial plugs are formed in the nasal cavities from
proliferation of the cells lining them. Between 13 to 15 weeks, the
nasal plugs disappear

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5.  The regions of continuity between the nasal and oral cavities are
the primordial choanae, which lie posterior to the primary palate.
 After the secondary palate develops, the choanae are located at
the junction of the nasal cavity and pharynx.
 While these changes are occurring, the superior, middle, and
inferior nasal conchae develop as elevations of the lateral walls of
the nasal cavities.
 .
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 Concurrently, the ectodermal epithelium in the roof of each nasal
cavity becomes specialized to form the olfactory epithelium.
 Some epithelial cells differentiate into olfactory receptor cells
(neurons).
 The axons of these cells constitute the olfactory nerves, which
grow into the olfactory bulbs of the brain

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Mesenchyme in the margins of the placodes proliferates,
producing horseshoe-shaped elevations-the medial and
lateral nasal prominences
the medial nasal prominences merge, they form an
intermaxillary segment

9. human embryo of
approximately 33 days.
FNP-frontonasal
prominance.
Venterolaterally (NP)-
nasal pit.
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10. •human embryo of
approximately 41 days.
•maxillary prominence
(MXP) appears puffed
up laterally and wedged
between the lateral
(LNP) and medial
(MNP) nasal
prominences
surrounding the nasal pit
(NP).
By Abera N (MSC)

11. Paranasal Sinuses
 They form from outgrowths or diverticula of the walls
of the nasal cavities and become pneumatic (air-filled)
extensions of the nasal cavities in the adjacent bones.
 The original openings of the diverticula persist as the
orifices of the adult sinuses.
 Some paranasal sinuses begin to develop during late fetal
life, such as the maxillary sinuses; the remainder of
them develop after birth.
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13. Developmental malformations of nasal
cavities and nose
 Absence of nose: no nasal placodes formation.
 A single nostril: only one nasal placode forms.
 Bifid nose: the medial nasal prominences do not merge completely. The
nostrils are widely separated and the nasal bridge is bifid.
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14. Development of Respiratory system
• The lower respiratory organs (larynx, trachea, bronchi, and lungs) begin
to form during the fourth week of development.
• Laryngotracheal diverticulum
– develop from laryngotracheal groove on the floor of primitive
pharynx at the level of 4-6th pharyngeal arches.
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17. Conti….
• Esophagotracheal septum by
fusion of esophagotracheal or
trachesophageal ridges(folds)
divides esophagus (dorsally)
from laryngotracheal tube
(ventrally).
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18. Conti….
• Laryngotracheal tube
• Give rise to the epithelium and glands of the lower respiratory organs.
• The connective tissue, cartilage, muscles, blood and lymphatic vessels
develop from surrounding mesoderm.
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19. Development of larynx
• Develops in the region of 4th- 6th pharyngeal arches.
Development of laryngeal cartilages.
– Arytenoids cartilage develops as the arytenoid
swelling from the cartilaginous component of the
arches.
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 Change vertical primitive glottis into a T- shaped opening.
 Other cartilages of the larynx also develop from the
cartilaginous component of the arches.
 The fourth and sixth pharyngeal arch cartilages fuse to
form the laryngeal cartilages except for the epiglottis. The
cartilage of the epiglottis develops from mesenchyme in the
hypopharyngeal eminence

21. Development of larynx
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22. Development of larynx
• Development of the laryngeal muscles
– Develop from muscular component of the pharyngeal arch's.
• Development of laryngeal cords
– During recanalization of the lumen, by the 10th week, the vocal and
vestibular folds and the ventricle located between form.
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23. Development of Trachea
• Develop from the laryngotracheal tube caudal to the
developing larynx.
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 The endodermal lining of the laryngotracheal tube distal to
the larynx differentiates into the epithelium and glands of
the trachea and the pulmonary epithelium.
 The cartilage, connective tissue, and muscles of the trachea
are derived from the splanchnic mesenchyme surrounding
the laryngotracheal tube

25. Development of Bronchi
• At 5th week right and left
primary bronchial buds grow
from the tracheal bud into
surrounding splanchnic
mesoderm located at the medial
walls of pericardioperitoneal
canals.
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26. Development of Bronchi
• The right bronchus
Is slightly wider and vertical.
Divides into superior and inferior branches, with the inferior branch
again dividing.
These will become the superior, middle and inferior lobar bronchi.
• The left bronchus divides and gives rise to superior and inferior
lobar bronchus.
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27. Development of Bronchi
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28. Development of the bronchial tree
• Division of the bronchi give segmental bronchi.
– Are 10 on the right and 8(9) on the left.
– With the surrounding mesenchymal tissue give rise to the primordial
of bronchpulmonary segments.
• By the 24th week about 17 orders of the bronchial tree are formed.
• Additional 6-7 orders of division occur after birth.
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29. Maturation of the lung
 Divided into four periods
1. Pseudoglandular period
2. Canalicular period
3. Terminal saccular period
4. Alveolar period
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30. Maturation of the lung in four periods
1. Pseudoglandular period
 6-16 weeks.
 Development of bronchi and
primordial terminal
bronchioles (establishment of
air conducting system).
 Resembles an exocrine gland.
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31. Maturation of the lung in four periods
2. Canalicular period
 15(16) to 26 weeks.
 Lumina of the bronchi and
terminal bronchioles become
larger.
 Development of
Terminal bronchioles
Respiratory bronchioles
Alveolar ducts
vasculature
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32. Maturation of the lung in four periods
3. Terminal saccular period
 26 weeks to birth.
 Development of many more
terminal saccules (primordial
alveoli)
 Differentiation of alveolar
epithelium, initially cuboidal
epithelium, then also squamous
at about 26 weeks.
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33. Maturation of the lung in four periods
3. Terminal saccular period (26
Weeks to Birth)
 Production of surfactant by type
two alveolar cells.
 Capillaries bulge in to developing
alveoli establishing the blood- air
–barrier.
 Premature born infant during this
period can survive for the blood-
air barrier has developed and
sufficient surfactant is available.
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34. Maturation of the lung in four periods
4. Alveolar period
 32 weeks to 8-10years.
 Maturation of alveoli by increase in
size and number of alveoli.
 Only 1/8-1/6 of adult number of
alveoli are present at birth.
 Adult number of about 300 million
alveoli is reached by the 8th years.
 Increase in size of the lung results
mainly by an increase in the number
of respiratory bronchioles and
alveoli.
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35. Development of lung
• Lungs begin function at birth.
• Before birth are half inflated by fluid derived from
amniotic fluid, and secretion from the lung and
tracheal glands. At birth this fluid is drained.
1. Through the mouth & nose by pressure on the
fetal thorax during the passage through the birth
canal.
2. Into the pulmonary capillaries and vessels.
3. In to the lymphatic vessels which are relatively
larger and more numerous in the fetus near term
than in the adult. By Abera N (MSC)

36. Development of lung
• Before birth, non- continuous breathing movements occur. These
cause;
1. Aspiration of some amniotic fluid into the lungs.
2. Stimulate lung development.
3. Exercise the respiratory muscles.
• Factors important for normal lung development;
1. Adequate thoracic space for lung growth.
2. Fetal breathing movement.
3. Adequate amniotic fluid volume.
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37. Development of the diaphragm
• Developed from the following four separate sources.
1. Septum transversum (transverse septum)
• Mesodermal tissue located cranial to the developing pericardial cavity.
• Descends to be located in between the right & the left pericardioperitoneal
canals, and also b/n the pericardial and peritoneal cavities.
• Gives rise to;
a. Central tendon of the diaphragm
• Also give rise to;
a. Ventral mesentery (& its derivatives) of the GIT.
b. Part of fibrous pericardium located on the diaphragm.
c. Parts of the pleura & peritoneum covering respectively the upper and lower aspects of
the diaphragm.
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39. Development of the diaphragm
b. Pleuroperitoneal membranes
Lateral expansion of the lungs also create right & left
pleuroperitoneal folds of mesenchymal tissue at the caudal end
of the pericardioperitoneal canal, dorsolateral to septum
transversum.
Expand medial and ventral direction to fuse with the septum
transversum & dorsal mesentery of esophagus.
Although form large portion of the fetal diaphragm, later represent
relatively small portions giving the muscular parts of the
diaphragm.
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41. Development of the diaphragm
C. Dorsal mesentery of esophagus
 Give rise to right & left crura of the diaphragm
D. Mesenchyme of the body wall
 As the result of expansion of the lungs, mesoderm of lateral body wall
splits in to two,
1. An external layer that becomes part of the definitive abdominal wall.
2. An internal layer that contribute to the peripheral part (costal margin)
of the diaphragm.
 In between the above two layers are the costodiaphragmatic recesses.
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42. Congenital anomalies of respiratory system
• Respiratory distrust syndrome(hyaline membrane
disease)
– Rapid and labored breathing shortly after birth.
– Mainly by deficiency in surfactant.
– Lungs are underinflated and the alveoli contain a
fluid of high protein content resembling a hyaline
(glassy) membrane.
• Laryngeal atresia
– By failure of recanalization of the larynx.
• Laryngeal web
– By incomplete recanalization of the larynx.
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43. Congenital anomalies of respiratory system
• Tracheo-esophagal
fistula
– By incomplete fusion
of the
tracheoesophageal
folds.
• Tracheal stenosis and
ateresia
– By unequal division of
the foregut into
esophagus and trachea.
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44. Congenital anomalies of respiratory system
• Agenesis of the lung(s)
– By failure of the lung buds to develop.
• Accessory lung (ectopic lung lobes)
– By additional respiratory bud from esophagus, trachea or stem
bronchus.
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45. Congenital Diaphragmatic Hernias
• Relatively common (1/2000 births)
• Hiatal hernias are most frequent,
but effects are rather minor due to
small size of defect
• Hernias due to failure of one or
both pleurpericardial membranes
to close off pericardioperitoneal
canals have much more significant
clinical impact because herniated
abdominal contents interfere with
lung development.
• 80-90% of hernias with clinical
impact are on the left side. Large
defects have high mortality due to
extent of lung hypoplasia and
dysfunction
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46. Congenital anomalies of respiratory system
• Hypoplasia of the lungs
– Associated with posterolateral diaphragmatic hernia
or eventration of the diaphragm.
– The abnormality positioned abdominal viscera
compress the lungs.
• Congenital cysts of the lung
– by dilation of terminal bronchi causing
sequestration of lung tissue.
• Neonatal lobar emphysema
– Failure of development of bronchial cartilages
causing the bronchi to collapse and over distension
of the lung lobes.
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