Transcript Development of respiratory system

Dr. Sama ul Haque
Objectives
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 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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Formation of the Lung Buds
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 In 4 weeks old embryo, the respiratory
diverticulum (lung bud) 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
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 The cartilaginous, muscular, and connective
tissue components of the trachea and lungs are
derived from splanchnic mesoderm surrounding
the foregut.
 The tracheoesophageal septum, divides the
foregut into a dorsal portion, the esophagus, and
a ventral portion, the trachea and lung buds.
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Development of Larynx
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 The internal lining of the larynx: From Endoderm
 The cartilages and muscles: From mesenchyme of the
4th and 6th Pharyngeal arches.
 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
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 Recanalization produce 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
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Pharyngeal arches: Each arch contains a cartilaginous component, a
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cranial nerve, an artery, and a muscular component.
Development of Trachea, Bronchi & Lungs
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 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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Maturation of the Lungs
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Maturation of the Lungs
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Development of Pleura
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 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
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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
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 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
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 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
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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
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 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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