Embryology - Respiratory System Development Flashcards
Describe the folding of the mesoderm?
Somatic mesoderm folds down to surround the splanchnic mesoderm of the intraembryonic body cavity/ coelom
What does splanchnic mesoderm and somatic mesoderm form?
Somatic - parietal
Splanchnic - visceral
What happen to yolk sac during folding of embryo laterally?
Yolk sac is absorbed into the primitive gut
What does folding of embryo give rise to?
Primitive gut tube
What does the gut tube form from?
Endoderm - foregut, midgut and hindgut
Where do lung buds develop from?
Foregut
Describe the formation of the trachea and lung buds
4 weeks - trachea and lung buds bud from wall of primitive foregut
Closely surrounded by splanchnic mesoderm
What is the relationship between oesophagus and trachea?
Trachea is anterior to oesophagus
What separates the trachea and lung buds from oesophagus
Oesophago-tracheal septum
What happens if trachea and lung buds do not seperate?
Tracheoesophageal fistula and oesophageal atresia
What is a fistula?
An abnormal passage between 2 epithelialized tubes or surfaces
TOF is common
What is an atresia?
A condition which an orifice or passage in the body is closed or absent
Describe the development of the pleura
Each lung bud invaginates the wall of the coelomic cavity and then grows to fill a greater part of the cavity
What does pleura develop from?
Lateral plate mesoderm
What forms the visceral pleura and parietal pleura?
Splanchnic forms visceral
Somatic forms parietal
What is the pericardioperitoneal canal?
Space around lungs between somatic and splanchnic mesoderm is continuous with the pericardial and peritoneal cavity
How is the sealing off of the pericardioperitoneal canal achieved?
Formation of pleuropericardial folds formed from the body wall and lines by somatic mesoderm
Once sealed off is known as pleural cavity
What are the stages of development of the lungs?
Embryonic - lung bud develops
Foetal - pseudoglandular, canalicular and saccular
Postnatal - alveolar
When is the pseudo-glandular stage?
7-17 weeks
What is the pseudo-glandular stage?
Development of the lung except the respiratory part
When is the canalicular stage?
17-27 weeks
What is the canalicular stage?
Formation of respiratory part
Alveolar ducts form and epithelium starts to differentiate into type 1 and 2 pneumocytes
Still no gas exchange
When is the saccular stage?
27-40 weeks
What is the saccular stage?
Formation of the alveolar sacs, primitive alveoli and surfactant - gas exchange begins
When is the alveolar stage?
32 weeks to 8 years postnatally
What is the alveolar stage?
Proliferation of the alveoli from alveolar sacs
Describe neonatal respiratory distress syndrome (hyaline membrane disease)
Caused by surfactant deficiency
Partial collapse of the alveoli
Debris consisting of blood elements accumulate to give glassy appearance
What is lung agenesis caused by?
Failure of lung bud to develop/ branch
Insufficient mesoderm Teratogens
Describe what is pulmonary hypoplasia
Incomplete development of the lungs, resulting in an abnormally low number or size of bronchopulmonary segments or alveoli
What closes off the pleural cavities from the peritoneal cavity of the abdomen?
Pleuroperitoneal folds/ membranes forming the diaphragm
What are the 4 mesodermal structures that the diaphragm develops from?
Septum transversum
Pleuroperitoneal folds
Skeletal muscle ingrowth from the peripheral body wall
The dorsal mesentery of the oesophagus
What does the septum transversum form?
This forms the central tendon of the diaphragm
Describe the pleuroperitoneal folds in the development of the diaphragm
Somatic mesodermal folds grow from peripheral body wall and fuse with septum transversum
They close off pleuroperitoneal canals - folds carry the lower intercostal nerves to supply the periphery of the diaphragm
What does the skeletal muscle ingrowth from peripheral body wall form?
Covers the pleuroperitoneal folds thus forming the muscular part of the diaphragm
Somites C3-5 carry phrenic nerve to muscular part
What does the dorsal mesentery of the oesophagus from of the diaphragm?
This structure attaches the embryological oesophagus to the posterior thoracic wall. Skeletal muscle from the periphery covers the dorsal mesentery to form the diaphragmatic crura.
What are some abnormalities of the diaphragm?
Oesophageal hiatus - hiatus hernia
Foramen of Bochdalek and Morgagni - diaphragmatic hernia
Explain a diaphragmatic hernia
Protrusion of n organ through the structure or muscle that usually contains it
Can compress left lung and push on heart and lungs
What does diaphragmatic hernia result in?
Pulmonary hypoplasia
