Development of Body Cavities and Diaphragm – Quiz

📌 Professor’s Notes: Quick Revision

High-yield revision notes for rapid review before university examinations.

• During the third week, small spaces develop within the lateral plate mesoderm and merge to form the primitive intraembryonic coelom. It eventually gives rise to the pericardial, pleural and peritoneal cavities.
• Formation of the coelom divides lateral plate mesoderm into somatopleuric mesoderm, related to ectoderm and body wall, and splanchnopleuric mesoderm, related to endoderm and viscera.

Development of Pericardial and Pleural Cavities

• The central part of the primitive coelom forms the pericardial cavity. With head folding, it shifts ventrally and lies between the stomodeum and septum transversum.
• The fibrous pericardium and parietal layer of serous pericardium develop from somatopleuric mesoderm, whereas the visceral layer of serous pericardium develops from splanchnopleuric mesoderm.
• The pericardioperitoneal canals lie on either side of the developing foregut and initially connect the pericardial and peritoneal cavities. As the lung buds expand into them, they enlarge and form the pleural cavities.
• Pleuropericardial membranes separate the pleural cavities from the pericardial cavity, while pleuroperitoneal membranes separate them from the peritoneal cavity. Closure of the pleuropericardial openings occurs around the sixth week.
• The visceral pleura develops from splanchnopleuric mesoderm covering the lungs, while the parietal pleura develops from somatopleuric mesoderm lining the thoracic wall.

Development of Peritoneal Cavity and Mesenteries

• The peritoneal cavity develops from the horseshoe-shaped limbs of the intraembryonic coelom. Lateral folding brings the two sides together to form a single abdominal peritoneal cavity.
• The parietal peritoneum develops from somatopleuric mesoderm, while the visceral peritoneum develops from splanchnopleuric mesoderm.
• A mesentery is a double layer of peritoneum that suspends abdominal viscera and provides a pathway for vessels, nerves and lymphatics. The dorsal mesentery persists widely, whereas the ventral mesentery largely regresses and remains mainly around the distal oesophagus, stomach and proximal duodenum.
• The lesser sac, or omental bursa, develops mainly from the right pneumoenteric recess within the dorsal mesogastrium. It lies posterior to the stomach and lesser omentum.
• Rotation of the stomach and development of the spleen produce important subdivisions of the lesser sac, including the superior, inferior and splenic recesses.

Development of Diaphragm

• The diaphragm develops from several embryonic components. The major contributors are the septum transversum, pleuroperitoneal membranes, dorsal mesentery of the oesophagus and lateral body wall mesoderm.
• The septum transversum forms an important early scaffold. The pleuroperitoneal membranes close the pleuroperitoneal canals and contribute significantly to the central tendon according to the chapter.
• The crura develop from the dorsal mesentery of the oesophagus. The muscular component develops from myoblasts migrating from cervical somites at C3 to C5, while the peripheral part develops from lateral body wall mesoderm.
• The diaphragm initially lies in the cervical region. As the embryo grows and the lungs and heart develop, it descends to the thoracoabdominal position while retaining its original cervical nerve supply. This explains the phrenic nerve supply from C3 to C5.

Congenital Anomalies

• Congenital diaphragmatic hernia results from defective formation of the diaphragm, allowing abdominal viscera to enter the thoracic cavity and causing pulmonary hypoplasia.
• Bochdalek hernia is a posterolateral diaphragmatic hernia and accounts for about 95 percent of congenital diaphragmatic hernias. It results from failure of closure of the pleuroperitoneal canal and occurs predominantly on the left side.
• Morgagni hernia is a retrosternal or parasternal hernia through the foramen of Morgagni, usually on the right side.
• Eventration of the diaphragm results from incomplete muscular development or abnormal elevation of a diaphragmatic dome. The diaphragm remains intact but becomes thin and weak.