Transcript 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.
2
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.
4

5
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.
6
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.
9
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.
10
Development of Larynx

Pharyngeal arches: Each arch contains a cartilaginous component, a
11
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.
13

14
Development of Trachea, Bronchi & Lungs

15
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.

17
Maturation of the Lungs

18
Maturation of the Lungs

19
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.
20
Development of Pleura

Growth of the lung buds into the pericardioperitoneal canals.
21
Note the pleuropericardial folds.
Development of Pleura

22
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.
23
The Visceral and Parietal Pleura

24
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).
25
Congenital anomalies of the Respiratory System

26
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.
27
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.
28
29