DEVELOPMENT OF BODY CAVITIES AND LUNGS

Question 1

What are the 3 body cavities?

Answer 1

Pleural cavity and pericardial make up the thorax

Peritoneal cavity makes up the abdomen

Question 2

Outline how the body cavities form?

Answer 2

The embryonic disc has polarity- the cranial region swells and starts to form neural tissue
There is a thinning of the trilaminar disc at the oropharyngeal membrane which will become the oral cavity. The trilaminar disc folds centrally like a drawstring [forming the gut tube) and the primitive heart (cardiac mesoderm) rotates around, dragging the oropharyngeal membrane with it.
A thinning at the caudal end will become the anus
Eventually, as the drawstring tightens further, an allantois forms as a temporary bladder
During this, the septum transversum rotates until it’s between the heart and yolk stalk at around 28 days to form the primitive diaphragm

Question 3

What will the septum transversum becomes?

Answer 3

The primordial diaphragm

Question 4

Why do we get pericardioperitoneal canals?

Answer 4

Because the septum transversum doesn’t totally meet the back wall of the body cavity so we get 2 canals either side of the lung bud

Question 5

How do pleurapericardial folds form?

Answer 5

Pleuropericardial membranes initially appear as small folds or ridges of mesenchyme projecting into the primitive thoracic cavity. The folds contain the common cardinal. Because of growth, the membranes are drawn out in a fold that extends from the lateral wall. The membranes fuse with the mesoderm ventral to the esophagus or primitive mediastinum and divide the thoracic cavity into a single pericardial cavity and 2 pleural cavities
The lung buds then grow into the medial walls of the pericardiopleural canals; and the pleural cavities expand around the heart into the body wall.