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The pleuroperitoneal canals close sequentially, with the right closing before the left, through the merging of mesothelial and mesenchymal folds. This developmental process is influenced by surrounding organs like the liver and lungs.
Area of Science:
- Developmental biology
- Embryology
- Anatomy
Background:
- The formation and closure of the pleuroperitoneal canals are critical events during fetal development.
- Understanding this process is essential for comprehending congenital diaphragmatic abnormalities.
Purpose of the Study:
- To chronologically describe the development and closure of pleuroperitoneal canals in fetal development.
- To elucidate the morphological changes and surrounding organ interactions during canal closure.
Main Methods:
- Light microscopy
- Transmission electron microscopy
- Scanning electron microscopy
- Study of 12.75- to 16-day-old fetuses
Main Results:
- Chronological events include lung bud projection, medial positioning, and canal shaping.
- The right pleuroperitoneal canal closes before the left (Right: 14.75-15 days; Left: 15-15.25 days).
- Closure involves the merging of dorsal and ventral fold mesothelia and mesenchyme, influenced by organ growth and positioning.
Conclusions:
- Pleuroperitoneal canal closure is facilitated by the pleuroperitoneal folds being pushed together.
- Organ enlargement (liver, thorax) and changes in canal orientation contribute to closure.
- This study provides a foundational understanding of pleuroperitoneal canal development in relation to adjacent structures.
Abstract:
Pleuroperitoneal canal development and closure were studied with light microscopy and transmission and scanning electron microscopy in 12.75- to 16-day fetuses. The major chronological events described in this paper are 1) the caudal tips of the lung buds projecting to the pleuroperitoneal canal (12.75 through 13.50 days); 2) the caudal tips of the lungs becoming situated medial to the canal areas at 14 days; and 3) both canals becoming crescent shaped with a uniform diameter until closure. Concurrently, the developing diaphragm and associated pleuroperitoneal folds assume more caudal positions. Both canal regions are bordered by the liver, lung, gonadal ridge, and suprarenal glands. In addition, on the left side, the stomach and mesogastrium also border the early canal. The right canal closes before the left (right, 14.75-15 days; left, 15-15.25 days). The results suggest that the pleuroperitoneal folds are pushed together, thereby closing the canals. This may be accomplished by one or a combination of the following: 1) enlargement of the liver pushing the ventral fold dorsad and a molding of the liver to the dorsal body wall caudal to the canal; 2) liver and thorax enlargement which appears to pull the dorsal fold taut against the central fold; and 3) a change in the orientation of the canal near the time of closure. Each canal is fully closed by the mergence of the dorsal and ventral fold mesothelia and mesenchyme. This study provides a basis for relating pleuroperitoneal canal development and closure to the surrounding organs and tissues.