Embryology 3 Flashcards
What are the 4 sections the development if the respiratory system is divided into?
1) Trachea
2) Lungs
3) Pleura
4) Diaphragm
What happens during the lateral folding of the embryo?
The somatic (parietal) mesoderm folds down to surround the
splanchnic (visceral) mesoderm of the intraembryonic body cavity/coelom.
The yolk sac becomes absorbed into the primitive gut .
Where does the trachea and the lungs develop from?
FOREGUT part of the primitive gut tube
What does folding of the embryo give rise to?
The primitive gut tube
What does the gut tube form from?
Endoderm –> foregut, midgut, hindgut
What happens at week 4?
Trachea and lung buds bud out from the ventral/anterior wall of the primitive foregut (endoderm).
What is the trachea and lung buds closely surrounded by?
Lateral plate splanchnic (visceral) mesoderm.
What does the foregut endoderm give rise to?
Lung bud
What does the lung bud give rise to?
Trachea and lungs
What will the pleura arise from?
The lateral plate mesoderm surrounding the lung bud
What develops between oesophagus and trachea completely separating them?
OESOPHAGOTRACHEAL SEPTUM –> ventral trachea and dorsal oesophagus
What if the trachea and oesophagus dont separate?
Tracheoesophageal fistula (TOF) and Oesophageal Atresia
- a common congenital abnormality
What type of condition is FISTULA?
an abnormal passage between 2 epithelialized tubes or surfaces.
What type of condition is ATRESIA?
a condition in which an orifice or passage in the body is closed or absent.
How is the pleural cavity formed?
Lung buds will push the splanchnic mesoderm towards the somatic mesoderm and become completely surrounded by both layers. The space between the two layers
will become the pleural cavity.
splanchnic layer of lateral plate mesoderm forms…
visceral pleura
What is the pericardioperitoneal canal
the space between the splanchnic and somatic mesoderm around the lungs is initially continuous with the pericardial and peritoneal cavity.
Somatic layer of lateral plate mesoderm forms…
Parietal pleura
How is the correct ventilatory pleural cavity pressures maintained?
Periocardioperitoneal canal is sealed off from the pericardial and peritoneal cavities by the formation of the pleuropericardial folds formed from the body wall and lined by somatic mesoderm
THE PLEURAL CAVITY IS NOW FORMED
Describe the 3 stages within the FETAL PERIOD
- Pseudoglandular stage (7 -17 weeks).
- Development of lung except respiratory part (no gas exchange) - Canalicular stage (17-27 weeks).
- Formation of respiratory part. Alveolar ducts form and epithelium starts to differentiate into Type I and Type II pneumocytes (still no gas exchange). - Saccular stage (27-40 weeks).
- Formation of alveolar sacs, primitive alveoli and surfactant (gas exchange begins).
What happens during the POSTNATAL period
- Alveolar stage (32 weeks to 8 years).
- Proliferation of alveoli from alveolar sacs.
- About95% of adult alveoli formed postnatally. 300m alveoli in adult
Name 3 congenital lung condition
Neonatal Respiratory Distress Syndrome (Hyaline Membrane Disease)
LUNG AGENESIS
PULMONARY HYPOPLASIA
What is neonatal respiratory distress syndrome caused by?
surfactant deficiency
partial collapse of alveoli
Debris consisting of blood elements accumulate – glassy (hyaline membrane) appearance
What is lung agenesis caused by?
- Failure of lung bud to develop/ branch
- Insufficient mesoderm
- Teratogens
What is pulmonary hypoplasia caused by?
Incomplete development of the lungs, resulting inan abnormally low number or size of bronchopulmonary segments or alveoli.
What does the diaphragm develop from?
4 mesodermal structures
How does the septum transversum form?
This forms the central tendon of the diaphragm
How does the Pleuroperitoneal folds form?
These somatic mesodermal folds grow in from the peripheral body wall to fuse with septum transversum. They close off the pleuroperitoneal canals, thus separating the pleural cavities from the peritoneal cavity. (Failure of these folds to form can result in herniation of adominal contents into the thorax). These folds carry the lower intercostal nerves to supply the periphery of the diaphragm
How does skeletal muscle ingrowth from the peripheral body wall grow?
This grows inwards to cover the pleuroperitoneal folds thus forming the muscular part of the diaphragm. From somites C3-C5 – these carry the phrenic nerve to the muscular part (phrenic nerve roots = C3, C4, C5.
What does the dorsal mesentery of the oesophagus attach?
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 forms the central tendon of the developing diaphragm?
Septum transversum
What happens if there is a failure of diaphragm to completely close during development?
Protrusion of an organ through the structure or muscle that usually contains it.
