Development of Body Cavities, Diaphragm & Serous Membranes

In which week does the intraembryonic coelom begin to develop?

3third week of development

Into which three parts does intraembryonic mesoderm differentiate?

• Paraxial mesoderm •

Intermediate mesoderm •

Lateral plate mesoderm

Where do the first cavities that form the intraembryonic coelom appear?

Vesicles in the lateral plate mesoderm

What happens to vesicles in the lateral plate mesoderm?

They fuse to form the intraembryonic coelom

What two layers does the intraembryonic coelom divide the lateral plate mesoderm into?

• Somatic mesoderm •

Splanchnic mesoderm

Which mesoderm forms the parietal layer of serous membranes?

Somatic mesoderm

Which mesoderm forms the visceral layer of serous membranes?

Splanchnic mesoderm

What shape does the early intraembryonic coelom have?

Horseshoe-shaped cavity

With which cavity does the early intraembryonic coelom communicate?

Extraembryonic coelom

What does the cranial part of the intraembryonic coelom become?

Primordium of the pericardial cavity

Where is the primordium of the pericardial cavity located?

• Cranial to the developing heart

• Caudal to the septum transversum

What is the septum transversum?

A mass of mesodermal tissue

What two major events occur due to embryonic folding?

• Separation of intraembryonic and extraembryonic coeloms

• Rotation of pericardial cavity, heart, and septum transversum

By how much do the heart, pericardial cavity, and septum transversum rotate?

180^{\circ}

After rotation, what is the new position of the septum transversum?

• Below the heart

• Forms caudal wall of the pericardial cavity

• Separates thoracic and abdominal regions (incompletely)

What are pericardioperitoneal canals?

• Two large openings

• On each side of the foregut

• Precursors of pleural cavities

Where do lung buds develop?

Pericardioperitoneal canals

What causes expansion of the pericardioperitoneal canals?

Rapid growth of lung buds

In which directions do the pericardioperitoneal canals expand?

• Dorsal

• Ventral

• Lateral

What membranes divide the thoracic cavity?

Pleuropericardial membranes

What structures are contained in pleuropericardial membranes?

• Common cardinal veins

• Phrenic nerves

What cavities result after pleuropericardial membrane fusion?

• One definitive pericardial cavity

• Two pleural cavities

Why do pleural cavities temporarily communicate with the abdominal cavity?

Diaphragm is incomplete

Which membranes close the thoracic–abdominal communication?

Pleuroperitoneal membranes