Diaphragm &ceolom

• Body Cavities


  • Thoracic cavity
  • Abdominopelvic cavity
• Thoracic cavity


  Contains one pericardial cavity and two pleural cavities
• Abdominopelvic cavity


  Contains one large peritoneal cavity
• Intraembryonic Coelom


  1. Appears as a horseshoe-shaped cavity in the cardiogenic area and lateral mesoderm by the 4th week

  2. The bend in this cavity indicates the future pericardial cavity and the limbs indicate the future pleural and peritoneal cavities

  3. The greater part of each limb opens laterally into the extra-embryonic coelom (EEC)
• Cranial folding of embryo

  The pericardial cavity comes to lie ventral to the foregut
• Pericardioperitoneal canals


  Arise from the dorsal wall of the pericardial cavity, pass on each side of the foregut (future esophagus), lie dorsal to septum transversum, and open into the peritoneal cavity
• Horizontal folding


  The limbs of the coelom are brought together on the ventral aspect of the embryo
• Coelom


  Lined by mesothelium derived from the somatic mesoderm (parietal layer) and the splanchnic mesoderm (visceral layer)
• Division of Embryonic Coelom

  1. Partitions appear to separate the pericardioperitoneal canals from the pericardial cavity and the peritoneal cavity

  2. As the lung buds grow into the pericardioperitoneal canals, a pair of membranous ridges is produced in the lateral wall of each canal: the pleuropericardial folds cranial to the developing lungs and the pleuroperitoneal folds caudal to the developing lungs
• Growth and descent of the heart and expansion of the pleural cavities


  1. The pleuro-pericardial membranes expand and move medially

  2. By 7th week, the membranes fuse with the mesenchyme ventral to the esophagus forming the primordial mediastinum, thus closing the pleuropericardial openings
• Pleuropericardial membranes


  Form the fibrous pericardium
• Development of Pleuroperitoneal Membranes

  1. Develop from the pleuroperitoneal folds that are attached dorsolaterally to the body wall and their free edges project into the caudal part of the pericardioperitoneal canals

  2. As the developing lung enlarges cranially and liver expands caudally, these folds become more prominent and gradually become membranous

  3. Are soon invaded by the myoblasts (primitive muscle cells)

  4. During 6th week, the pleuroperitoneal membranes extend ventromedially and fuse with the dorsal mesentery of the esophagus and the septum transversum, resulting in closure of the pericardioperitoneal openings
• Mesentery


  Double layer of peritoneum enclosing a mass of mesoderm, connects the organ to the body wall, carries vessels, nerves & lymphatics for the organ, site where the visceral peritoneum continues as parietal peritoneum
• Embryonic components of the diaphragm

  • Septum transversum
  • Pleuroperitoneal membranes
  • Dorsal mesentery of esophagus
  • Muscular ingrowth from lateral body walls
• Septum Transversum


  A thick plate of mesodermal tissue located between the pericardial cavity and the yolk sac, ventral to the foregut and the pleuro-peritoneal canals, grows dorsally from the ventrolateral body wall, forms an incomplete partition between the thoracic cavity and the abdominal cavity, expands and fuses with the pleuroperitoneal membranes and the mesenchyme ventral to the esophagus, is the primordium of the central tendon of the diaphragm
• Fusion of diaphragm components

  1. During 6th week, the pleuroperitoneal membranes, mesoesophagus, and septum transversum fuse with each other and form a complete partition between the thoracic and abdominal cavities

  2. During 9th - 12th weeks, the lungs and pleural cavities enlarge, burrowing into the body wall, splitting it into an external layer that becomes part of the body wall and an internal layer that contributes muscles to peripheral portions of diaphragm, extending to the parts derived from the pleuroperitoneal membranes
• Diaphragm


  • Body wall: peripheral muscular part
  • Pleuroperitoneal membranes: form large portion of fetal diaphragm but represent a smaller portion in infants
  • Septum transversum: Central tendon
  • Dorsal mesentery of esophagus: Crura
• Positional Changes and Innervation of the Diaphragm

  1. During 4th week, the septum transversum lies opposite the 3rd - 5th cervical somites

  2. During 5th week, myoblasts from these somites move to the developing diaphragm bringing their nerve fibers with them

  3. By 6th week, the diaphragm lies at the level of the thoracic somites

  4. By end of 8th week, the dorsal end of diaphragm lies at the level of first lumbar vertebra

  5. When the 4 parts of the diaphragm fuse, the mesenchymal cells from the septum transversum extend into the other three parts, change into myoblasts, and give rise to the muscles of the diaphragm

  6. The phrenic nerve supplies all the muscles of diaphragm, except in the peripheral region which is derived from the body wall and brings its nerve supply (lower intercostal nerves) with it
• Congenital Anomalies of the Diaphragm


  • Eventration of diaphragm: because of defective musculature
  • Congenital hiatal hernia: because of large esophageal hiatus
  • Congenital diaphragmatic hernia: Commonly through a posterolateral defect in diaphragm, mostly on left side, left lung shows hypoplasia