Development of Respiratory System• It begins at the end of third week by formation of

endodermal laryngo-tracheal groove at floor of pharynx caudal to hypobranchial eminence.

• Laryngotracheal tube is separated from foregut by formation of tracheo-esophageal septum. This tube elongates till the thorax.

• Upper part of the tube forms the mucus membrane of larynx while lower part form mucus membrane of trachea and bronchi.

• The lower end of the tube will divides to form 2 lung buds.

• Surrounding mesoderm will form muscles and cartilages of larynx and trachea.

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Formation of Lungs• Each lung bud divides into 3 branches, but on left

side one of the branches disappears. Right lung has 3 lobes, left lung has 2 lobes.

• Each branch of the lung bud divides repeatedly to form bronchioles and lastly alveoli.

• Blood vessels are formed from surrounding mesoderm.

• Lung invades pleura from medial aspect, so pleura surrounds lung by 2 layers.

• Expansion of lung occurs after birth when the baby takes his first inspiration

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2 lingual swellings

Tuberculum impar

Foramen ceacum

Copula

Hypobranchial eminence

Laryngeo-trachial groove

Pharynx

Respiratory diverticulum

Dr. Sherif Fahmy

Laryngeo-tracheal duct

esophagusDr. Sherif Fahmy

Laryngo-tracheal duct

Foregut Tracheo-esophageal ridges

Lung buds

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Congenital Anomalies• 1- Tracheo-oesphageal fistula: Due to

incomplete formation of tracheo-oesophageal septum.• 2- variations in branching of lung bud:

Leads to extra or missed lobe and may be missed lung.• 3- Congenital cyst.• 4- Esophageal atresia.• 5- Respiratory distress syndrom.

Dr. Sherif Fahmy