Development of Respiratory System

الرحمن الله بسمالرحيم

Respiratory system

UpperRespiratory

system

LowerRespiratory

system

Nose Pharynx Larynx TracheaBronchi Lungs

Prof. Mohamed AutifiProf. Mohamed Autifi

The lower respiratory system develops as Median laryngo-laryngo-tracheal groovetracheal groove in the floor of pharynx between the 6th pharyngeal arches(26th – 27th day)

Prof. Mohamed AutifiProf. Mohamed Autifi

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 AutifiProf. Mohamed Autifi

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 AutifiProf. Mohamed Autifi

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 AutifiProf. Mohamed Autifi

Cartilages:Cartilages:Epiglottis: from the caudal part of hypobranchial

eminence.The rest of the cartilages: from 4th and 6th arch.

Muscles:Muscles:Cricothyroid : from the 4th pharyngeal arch.Other muscles: from the 6th pharyngeal arch.

Mucous membrane: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 AutifiProf. Mohamed Autifi

Congenital anomalies of lungsCongenital 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 stem of lung bud.3. Abnormal division of bronchial tree: leading to super-numerary lobules. 4. Ectopic lung lobes: arise from trachea or oesophagus, due to abnormal budding.5. Congenital cysts of the lung: due to dilation

of terminal or larger bronchi. 6. Respiratory distress syndrome: failure of the

alveoli to ventilate due to absence of surfactant.

Prof. Mohamed AutifiProf. Mohamed Autifi

6. Tracheo-oesophageal fistula:

due to incomplete fusion of the lips of laryngo- tracheal groove.

Prof. Mohamed AutifiProf. Mohamed Autifi