BODY CAVITIES, MESENTERIES & DIAPHRAGM

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 • 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 cervical 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)