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# Development of the Diaphragm The image describes the development of the diaphragm, a crucial muscle in respiration. Here's a breakdown of the key components and their roles: ## Key Structures and Their Functions **1. Septum transversum:** - A thick mass of mesoderm positioned between the prim...

# Development of the Diaphragm The image describes the development of the diaphragm, a crucial muscle in respiration. Here's a breakdown of the key components and their roles: ## Key Structures and Their Functions **1. Septum transversum:** - A thick mass of mesoderm positioned between the primitive heart tube and the developing liver. - It's the precursor to the central tendon of the diaphragm. **2. Paired pleuroperitoneal membranes:** - Sheets of somatic mesoderm. - These membranes give rise to the crura of the diaphragm. **3. Dorsal mesentery of the esophagus:** - Forms the crura of the diaphragm in the adult. **4. Lateral body wall:** - Supplies muscle to the peripheral portions of the definitive diaphragm. ## Diagram Description The diagram shows a cross-sectional view of the developing human embryo, highlighting the components involved in diaphragm formation. It illustrates the closure of the pericardioperitoneal canal through the growth of pleuroperitoneal membranes, indicated by arrows. These membranes link the septum transversum (a crucial structure in the development of the diaphragm) to the posterior body wall, ultimately sealing off the pleural cavities from the peritoneal cavity. ## Closure of the Pericardioperitoneal Canals * **Between weeks 5 and 7:** A pair of horizontal pleuroperitoneal membranes grow from the posterior body wall to connect with the septum transversum. This closure subsequently seals off the pleural cavities from the peritoneal cavity. * **The membranes:** Form the posterior portions of the diaphragm. * **Arrows (diagram B):** Indicate the subsequent invasion of the developing diaphragm by muscle tissue (fibers) from the surrounding body wall. **References:** * Human Embryology and Developmental Biology, By Carlson, 3rd Edition * Human Embryology, By Larsen, 5th edition