development of respiratory system (special embryology)
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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.
Dr. Sherif Fahmy
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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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Dr. Sherif Fahmy
2 lingual swellings
Tuberculum impar
Foramen ceacum
Copula
Hypobranchial eminence
Laryngeo-trachial groove
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Pharynx
Respiratory diverticulum
Dr. Sherif Fahmy
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Laryngeo-tracheal duct
esophagusDr. Sherif Fahmy
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Laryngo-tracheal duct
Foregut Tracheo-esophageal ridges
Lung buds
Dr. Sherif Fahmy
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Dr. Sherif Fahmy
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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.
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Dr. Sherif Fahmy