Body Cavities, Mesenteries &

Diaphragm Speaker:陳玉怜

Peritoneal cavity

Pleural cavity Pericardial cavity 3 week

paraxial ectoderm mesoderm

*extraembryonic * coelom *chorionic cavity lateral mesoderm (yolk sac)

18 day embryo

lateral mesoderm * intraembryonic coelom: cardiogenic area & lateral mesoderm

*

* intraembryonic 20 day coelom *Intraembryonic coelom horseshoe-shaped cavity -Curve  future pericardial cavity -Limbs  future pleural & peritoneal cavities *

intraembryonic coelom *  Distal part of each limb -- at the lateral edges of the embryonic disc -- extraembryonic coelom

*

early in the 4th week Folding of the embryo

Tail fold Head fold

pericardial coelom

Lateral fold Lateral fold *

22 d

Intraembyonic coelom & Embryonic Foldings

~26 days

*

* dorsal mesentery ventral mesentery except where it is attached to caudal foregut (future stomach & proximal duodenum)

~28 days  19 D 20 D

End of 4 week Embryonic body cavity • Somatic mesoderm parietal wall future parietal layer of peritoneum • Splanchnic mesoderm visceral wall future visceral layer of peritoneum Pericardioperitoneal Canal Pericardioperitoneal Canals

~24 days

-- Each lies lateral to foregut (future esophagus) and dorsal to septum transversum (primordial central tendon of diaphragm). • In lateral wall of each pericardioperitoneal canal: -*cranial ridge: pleuropericardial fold pleuropericardial membrane (contain common cardinal veins) - caudal ridge: pleuroperitoneal fold pleuroperitoneal membrane (diaphragm)

5 wks 6 wks • During the 7th week, pleuropericardial membranes fuse with the mesenchyme ventral to esophagus ‐‐ Forming primordial mediastinum. ‐‐ Separating pericardial cavity from pleural cavities. • ‐‐extend into body wall, splitting the mesenchyme into: • outer layer  thoracic wall inner layer  fibrous pericardium

7 wks 8 wks Beginning of 5th W

Diaphragm 

Head Fold  



septum transversum

Pleuroperitoneal Membranes  Separates the pleural cavities from peritoneal cavity

End of 5th wk End of 6th wk 12th wk

Ventral Dorsal mesentery of esophagus Muscular ingrowth from lateral body walls Body wall tissue is added peripherally to the diaphragm as the lungs and pleural cavities enlarge

肋橫膈隱窩; CP angle Positional Changes & Innervation of the Diaphragm phrenic nerves- ventral rami of the 3rd, 4th, & 5th cervical spinal nerves phrenic nerves -30 cm long in adults the beginning of the 8th week

4th week 6th week CONGENITAL DIAPHRAGMATIC HERNIA (CDH, 疝)

•Prenatal diagnosis: Ultrasound & magnetic resonance imaging of abdominal organs in thorax.

Posterolateral defect Defective muscular development Herniation of liver Herniation of stomach and bowel Summary (I) 1. the end of the 3rd week: Intraembryonic coelom begins to develop. 2. By the 4th week:  a horse-shoe-shaped cavity in cardiogenic & lateral mesoderm. The right & left part of the intraembryonic coelom  peritoneal cavity. 3. the 7th week: pericardial cavity paired pericardioperitoneal canals  peritoneal cavity Summary (II)

4. During the 5th & 6th weeks, folds (later membranes) form near the cranial & caudal ends of these canals. 5. By the end of the 6th week, fusion of the caudal pleuroperitoneal membranes during formation of the diaphragm  separates the pleural cavities from the peritoneal cavity. Summary (III) 6. By the 7th week, Fusion of the cranial pleuropericardial membranes with mesoderm ventral to the esophagus separates the pericardial cavity from the pleural cavities. 7. The diaphragm develops from 4 structures.