1. BODY CAVITIES,
MESENTERIES &
DIAPHRAGM
Dr. Ahmed Fathalla Ibrahim

2. INTRAEMBRYONIC COELOM

3. INTRAEMBRYONIC COELOM
Appears as isolated spaces in the lateral mesoderm
In the 4th week, the spaces fuse to form a single horseshoe-shaped (U-shaped) cavity
The coelom divides the lateral mesoderm into:
Somatic (parietal) layer: under ectoderm
Splanchnic (visceral) layer: over endoderm
Somatopleure = somatic mesoderm + overlying ectoderm
Splanchnopleure = splanchnic mesoderm + underlying endoderm

4. INTRAEMBRYONIC COELOM

5. INTRAEMBRYONIC COELOM
DERIVATIVES: It gives rise to three body cavities:
A pericardial cavity: the curve of U
Two pericardioperitoneal canals (future pleural cavities): the proximal parts of the limbs of U
Two peritoneal cavities: the distal parts of the limbs of U
Each cavity has a parietal layer (derived from somatic mesoderm) & a visceral layer (derived from visceral mesoderm)
FUNCTION: It provides space for the organs to develop & move

6. DEVELOPMENT OF PERITONEAL CAVITY
Major part of intraembryonic coelom
Develop from the distal parts of the limbs of the U-shaped cavity
Originally, it is connected with extraembryonic coelom (midgut herniates to the outside through this connection)
At 10th week, it looses its connection with extraembryonic ceolom (when midgut returns to abdomen)

7. DEVELOPMENT OF PERITONEAL CAVITY
Originally, there were 2 peritoneal cavities
After lateral folding of embryo, the peritoneum becomes a single cavity
HOW?

9. Dorsal
Mesentery
Gut
Peritoneal
Cavity
Ventral
Mesentery

10. MESENTERIES
A MESENTERY is a double layer of peritoneum that begins as an extension of the visceral peritoneum covering an organ
The mesentery connects the organ to the body wall and transmits vessels and nerves to it
Transiently, the dorsal & ventral mesenteries divide the peritoneal cavity into right & left halves
The ventral mesentery disappears EXCEPT where stomach develops
(WHY?)

12. PERICARDIAL CAVITY Develops from the curve of the U-shaped cavity
During formation of head fold, the heart & pericardial cavity move ventrocaudally & become anterior to the foregut (esophagus)
It is bounded by an outer somatic & an inner visceral layer, forming the serous pericardium

13. PERICARDIAL CAVITY HOW?
Originally, it is connected with the 2 pericardioperitoneal canals
Later on, it become separated from the 2 pericardioperitoneal canals
HOW?

15. PERICARDIAL CAVITY
Originally, the bronchial buds are small relative to the heart
Bronchial buds grow laterally into pericardioperitoneal canals (future pleural cavities)
Pleural cavities expand ventrally around heart & splits mesoderm into:
Outer layer: forms thoracic wall
Inner layer: pleuropericardial membrane

16. PLEUROPERICARDIAL MEMBRANES
THE PARTS SURROUNDING THE SEROUS PERICARDIUM: form the fibrous pericardium
THE PARTS BEHIND THE HEART: fuse with the ventral mesentery of the esophagus (at 7th week), forming the mediastinum & separating pericardial from pleural cavities
N.B.: The right pleural cavity separates from pericardial cavity earlier than left

17. PLEURAL CAVITIES Develop from the 2 pericardiperitoneal canals
Originally, they are connected with pericardial & peritoneal cavities
Later on, they become separated from:
Pericardial cavity
Peritoneal cavity (HOW?)

19. PLEUROPERITONEAL MEMBRANES
Produced when developing lungs & pleural cavities expand into the body wall
During 6th week, they fuse with dorsal mesentery of esophagus & septum transversum, separating pleural cavities from peritoneal cavity
N.B.: The right pleural cavity separates from peritoneal cavity earlier than left

20. DEVELOPMENT OF DIAPHRAGM

21. DEVELOPMENT OF DIAPHRAGM
The diaphragm develops from:
Septum transversum: forms the central tendon
Dorsal mesentery of esophagus: forms the right & left crus
Muscular ingrowth from lateral body wall: posterolateral part (costal part)
Pleuroperitoneal membranes: small portion of diaphragm

22. SEPTUM TRANSVERSUM
At 3rd week, it is in the form of mass of mesodermal tissue in the cranial part of embryo (opposite the 3rd, 4th & 5th cervical somites)
At 4th week (during formation of head fold), it moves ventrocaudally forming a thick incomplete partition between thoracic & abdominal cavities
At 6th week, it expands & fuse with dorsal mesentery of esophagus & pleuroperitoneal membranes to form the diaphragm

23. INNERVATION OF DIAPHRAGM
Myoblasts from 3rd, 4th & 5th somites migrate into diaphragm & bring their nerve fibers from them
Nerve fibers derived from ventral rami of 3rd, 4th & 5th cervical nerves fuse to form phrenic nerve that elongate to follow the descent of diaphragm
Both motor & sensory supply of the diaphragm is derived from phrenic nerve
The part of diaphragm derived from lateral body wall receives sensory fibers from lower intercostal nerves

24. ANOMALIES OF DIAPHRAGM
CONGENITAL DIAPHRAGMATIC HERNIA
EVENTRATION OF DIAPHRAGM
CONGENITAL HIATAL HERNIA

25. CONGENITAL DIAPHRAGMATIC HERNIA

26. CONGENITAL DIAPHRAGMATIC HERNIA
A posterolateral defect of diaphragm
Cause: defective formation and/or fusion of pleuroperitoneal membrane with other parts of diaphragm
Effects:
Herniation of abdominal contents into thoracic cavity
Peritoneal & pleural cavities are connected with one another
The defect usually occurs in the left side (WHY?)

27. EVENTRATION OF DIAPHRAGM

28. EVENTRATION OF DIAPHRAGM
Cause: failure of muscular tissue from body wall to extend into pleuroperitoneal membrane on one side
Effects: superior displacement of abdominal viscera (surrounded by a part of diaphragm forming a pocket)

29. CONGENITAL HIATAL HERNIA
Herniation of part of the stomach through a large esophageal hiatus (opening)