Download Development of respiratory system

Dr. Sama ul Haque
Objectives

 Discuss the formation of the lung buds.
 Describe the development of larynx.
 Explain the mechanism of formation of trachea,
bronchi and lungs.
 Differentiate between the periods of lung
maturation.
 Discuss the congenital anomalies of the
respiratory system.
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Respiratory System
Upper respiratory tract:
Nose
Nasal cavity &
paranasal sinuses
Pharynx
Lower respiratory tract:
Larynx
Trachea
Bronchi
Lungs
Formation of the Lung Buds

 In 4 weeks old embryo, the respiratory diverticulum
(lung bud) = The laryngeotracheal diverticulum appears
as an outgrowth from the ventral wall of the foregut.
 Epithelium of the internal lining of the larynx, trachea,
and bronchi, as well as that of the lungs, is entirely of
endodermal origin.
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Formation of the Lung Buds

 The cartilaginous, muscular, and connective
tissue components of the trachea and lungs are
derived from splanchnic mesoderm surrounding
the foregut.
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A longitudinal
tracheo-esophageal
septum develops and
divides the
diverticulum into a:
Dorsal portion:
primordium of the
oropharynx and
esophagus
Ventral portion:
primordium of
larynx, trachea,
bronchi and lungs
The proximal part of
the respiratory
diverticulum
remains tubular and
forms larynx &
trachea.
The distal end of the
diverticulum dilates
to form lung bud,
which divides to give
rise to 2 lung buds
(primary bronchial
buds)
Development of the Larynx
 The internal lining of the larynx: glands
and epithelium, develops from Endoderm

 The cartilages and muscles: From
mesenchyme of the 4th and 6th Pharyngeal
arches.
 The opening of the laryngotracheal
diverticulum into the primitive foregut
becomes the laryngeal orifice.
 Proliferating mesenchyme of the two
arches transforms into the thyroid,
cricoid, and arytenoid cartilages.
 Temporary occlusion of the laryngeal
lumen occurs due to the proliferation of
laryngeal epithelium.
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Development of Larynx
 Recanalization produces a pair of lateral
recesses, the laryngeal ventricles
(recesses are bounded by folds of tissue
that differentiate into the false and true
vocal cords).

 Since musculature of the larynx is derived
from mesenchyme of the 4th & 6th
pharyngeal arches, all laryngeal muscles
are innervated by branches of the 10th
cranial nerve (vagus nerve).
 The superior laryngeal nerve innervates
derivatives of the fourth pharyngeal arch,
and
 the recurrent laryngeal nerve innervates
derivatives of the sixth pharyngeal arch.
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Development of Larynx

Pharyngeal arches: Each arch contains a cartilaginous component, a
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cranial nerve, an artery, and a muscular component.
Development of the Trachea
The endodermal lining
of the laryngotracheal
tube distal to the larynx
differentiates into the
epithelium and glands of
the trachea and
pulmonary epithelium
The cartilages,
connective tissue, and
muscles of the trachea are
derived from the
mesoderm.
Development of Trachea, Bronchi & Lungs

 During its separation from the foregut, the lung bud
forms the trachea and two lateral outpocketings, the
bronchial buds.
 At the beginning of the 5th week, each of these buds
enlarges to form right and left main bronchi.
 The right then forms three secondary bronchi, and the
left, two.
 By the end of the 6th month, approximately 17
generations of subdivisions have formed. Before the
bronchial tree reaches its final shape, however, an
additional six divisions form during postnatal life.
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Development of Trachea, Bronchi & Lungs

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The right main
bronchus is slightly
larger than the left
one and is oriented
more vertically
The embryonic
relationship persists
in the adult.
The main bronchi
subdivide into
secondary and
tertiary (segmental)
bronchi which give
rise to further
branches.

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Maturation of the Lungs

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Maturation of the Lungs

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Development of Pleura

 The pleuroperitoneal and pleuropericardial folds separate
the pericardioperitoneal canals from the peritoneal and
pericardial cavities, respectively, and the remaining
spaces form the primitive pleural cavities.
 The splanchnic mesoderm, which covers the outside of
the lung, develops into the visceral pleura.
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Development of Pleura

Growth of the lung buds into the pericardioperitoneal canals.
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Note the pleuropericardial folds.
Development of Pleura

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Development of pleura

 The somatic mesoderm layer, covering the body
wall from the inside, becomes the parietal pleura.
 The space between the parietal and visceral pleura
is the pleural cavity.
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The Visceral and Parietal Pleura

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Congenital anomalies of the Respiratory System

 Abnormalities in partitioning of the esophagus
and trachea by the tracheoesophageal septum
result in esophageal atresia with or without
tracheoesophageal fistulas (TEFs).
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Congenital anomalies of the Respiratory System

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Congenital anomalies of the Respiratory System


Respiratory distress syndrome (RDS) or
(Hyaline membrane disease): When surfactant is insufficient,
the air-water (blood) surface membrane tension becomes high,
so alveoli will collapse during expiration.
 Blind-ending trachea with absence of lungs.
 Agenesis of one lung.
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Congenital anomalies of the Respiratory System

 Abnormal divisions of the bronchial tree.
 Ectopic lung lobes arising from the trachea or
esophagus from additional respiratory buds of the
foregut that develop independently of the main
respiratory system.
 Congenital cysts of the lung, which are formed by
dilation of terminal or larger bronchi.
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