3. The lower respiratory
system develops as
Median laryngo-tracheal
groove in the floor of
pharynx between the 6th
pharyngeal arches
(26th – 27th day)
Prof. Mohamed Autifi
4. Laryngo-tracheal groove deepens
➪ laryngo-tracheal diverticulum
(respiratory diverticulum)
The edges of it fuse ➪
oesophago-tracheal septum,
which converts the groove into
laryngo-tracheal tube, separates
it dorsally from oesophagus
Prof. Mohamed Autifi
5. The cranial part of the
laryngotracheal tube
becomes the larynx which
opens into the pharynx by
laryngeal orifice.
The caudal part separates
from the related part of
the foregut (oesophagus)
and divides into the two
principle bronchi.
Each bronchus is divided into
2ry and then 3ry bronchial
buds and surrounded by a
mesodermal mass and is
called the lung bud.
Prof. Mohamed Autifi
6. The
cartilages and muscles of larynx develop mainly
from the mesoderm of the 4th and 6th pharyngeal arches.
The cartilages and muscles of the trachea and
bronchi develop from the splanchnic mesoderm which
surround the laryngo-tracheal tube.
Each lung bud branches into bronchi, bronchioles and
alveoli of the lung.
The surrounding mesoderm forms the stroma and
blood vessels of the lung.
The pleura is formed a part of intraembryonic coelom.
Prof. Mohamed Autifi
7. Cartilages:
Epiglottis:
from the caudal part of hypobranchial
eminence.
The rest of the cartilages: from 4th and 6th arch.
Muscles:
Cricothyroid
: from the 4th pharyngeal arch.
Other muscles: from the 6th pharyngeal arch.
Mucous membrane:
Supraglottic
area: from the 4th pharyngeal arch
(supplied by superior laryngeal nerve).
Infraglottic area: from the 6th pharyngeal arch
(supplied by recurrent laryngeal nerve).
Prof. Mohamed Autifi
8. Congenital anomalies of lungs:
1. Agenesis of one or both lungs: due to failure of
development of lung buds.
2. Accessory lung lobes: due to additional branching of
3.
4.
5.
6.
stem of lung bud.
Abnormal division of bronchial tree:
leading to super-numerary lobules.
Ectopic lung lobes: arise from trachea or
oesophagus, due to abnormal budding.
Congenital cysts of the lung: due to dilation of
terminal or larger bronchi.
Respiratory distress syndrome: failure of the alveoli
to ventilate due Prof. Mohamed Autifi of surfactant.
to absence
Prof. Mohamed Autifi
