22. Embryology Flashcards
Describe how the lungs initially form
Around week 4 an out-pouching is formed from the oesophagus (an endodermal structure). This is known as the respiratory diverticulum
What occurs in the further development in week 4
The tracheoesophageal septum forms separating the lungs from the oesophagus
The diverticulum forms two buds which proliferate into secondary and tertiary bronchi
How does a tracheoesopageal fistula occur?
The septum does not form properly or does not form at all.
Common abnormalities include:
- Oesophagus empties into the trachea
- Oesophagus is blind ended proximally and arises from the carina distally
Describe what happens in weeks 8-16
Bronchial buds branch off from tertiary bronchi and proliferate
There is no alveoli so no gas exchange. However the tissue is still metabolically active and is able to remove large amounts of oxygen from the blood
What is the job of the ductus arteriosus
Due to the fact the lungs take so much oxygen the ductus arteriole shunts blood from the pulmonary artery to the aortic arch, restricting the blood the lungs receive.
Describe how the pleura develop
Splachnic mesoderm forms visceral pleura
Somatic mesoderm forms parietal pleura
Gaps between visceral and parietal pleura are called the pleuroperitoneal canals
Describe the development of the alveoli
From 26 weeks onwards the alveoli develop. Importantly they produce surfactant an amphipathic molecule that binds to water and air in the lungs, easing the work of breathing.
Infants born prematurely struggle to survive due to a reduction in surfactant produced. This is called infant respiratory distress syndrome (IRDS)
Describe how the diaphragm develops?
Develops from the top of the neural tube from the septum transversum but during folding it move under the primitive heart taking the supply from C3,4 and 5, forming the precursor of the phrenic nerve.
