Development of the Diaphragm

  • Overview

    The diaphragm is a fibromuscular partition that separates the thoracic cavity from the abdominal cavity. It is a major muscle of respiration and it arises from four primordia.

    • Septum transversum - forms the anterior part of the diaphragm including most of the central tendon
    • Pleuroperitoneal membranes - forms the posterior part of the diaphragm by closing the pericarioperitoneal canals
    • Mesentery of the esophagus - forms the crura of the diaphragm, in particular the right crus.
    • Body wall myoblasts - forms the muscular rim of the diaphragm

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    View of the inferior surface of the adult diaphragm showing which parts are derived from each of the four primordial

  • Septum Tranversum

    The septum transversum begins to condense from mesoderm during the third week of development. It appears in the cervical region and is innervated by cervical spinal nerves. As the embryo folds in the rostral and caudal directions the septum transvernsum is displaced caudally in the embryo but carries its original nerve supply with it. This explains why the phrenic nerve, the main nerve supply to the diaphragm consists of axons from spinal nerves C3, C4, and C5.

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    In this embryo we are looking up at the inferior surface of the septum transversum, which is located anteriorly in the embryo and which partially separates the developing abdomen from the developing thorax. The esophagus passes posterior to it and the mesentery of the esophagus is connected to it. Pericardioperitoneal canals connect the peritoneal cavity (abdomen) with the thoracic cavity (pleural cavity) on either side of the midline. Completion of the diaphragm is by closure of the pericardioperitoneal canals by the growth of a pair of pleuroperitoneal membranes.

  • Pleuroperitoneal Membranes

    In this embryo we are looking up at the inferior surface of the developing diaphragm. Pericardioperitoneal canals connect the peritoneal cavity (abdomen) with the thoracic cavity (pleural cavity) on either side of the midline. Completion of the diaphragm is by closure of the pericardioperitoneal canals by the growth of a pair of pleuroperitoneal membranes. Failure of one of the other of these membranes to develop leads to the development of congenital diaphragmatic hernias.

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  • Mesentery of the Esophagus
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    The mesentery of the esophagus, which attaches the esophagus to the septum transversum anteriorly and the body wall posteriorly, forms the two crura of the diaphragm. The crura of the diaphragm are stout, muscular columns of tissue that anchor the diaphragm to the bodies of lumbar vertebrae.
    The hiatus for the passage of the esophagus from thorax to abdomen is located within the right crus of the diaphragm.

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  • Body Wall Myoblasts

    The posterior part of the edge of the diaphragm is muscular and is developed from myoblasts derived from the body wall.

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