Embryology · Respiratory system, diaphragm and body cavities
Intraembryonic coelom: pericardial, pleural and peritoneal cavities !
- Embryonic structure
The embryo has one large cavity that later splits into three: one for the heart, two for the lungs and one for the abdomen.
Updated 2026-11-01
See it in 3D: Pleura · Pericardium · Peritoneum · Diaphragm · Phrenic nerves
What it is
The intraembryonic coelom appears in week 3 when lateral plate mesoderm splits into a somatic and a splanchnic layer. With folding in week 4 it becomes one continuous cavity from chest to pelvis. The pleuropericardial folds and the pleuroperitoneal membranes divide it into the pericardial cavity, two pleural cavities and the peritoneal cavity, all lined by serous membranes.
Structure
- Week 3: spaces appear in lateral plate mesoderm, join up and split it into somatic and splanchnic layers.
- Week 4: lateral and head-to-tail folding closes the ventral wall and turns the space into a tube-shaped cavity.
- The septum transversum lies under the heart and partly separates the primitive pericardial cavity from the peritoneal one.
- The lung buds grow into the pericardioperitoneal canals, which become the pleural cavities.
- The pleuropericardial folds fuse in the midline and close off the pericardial cavity.
- The pleuroperitoneal membranes close the canals around week 7 and separate chest from abdomen.
What it becomes
- Somatic layer: parietal pleura, parietal serous pericardium and parietal peritoneum.
- Splanchnic layer: visceral pleura, epicardium and visceral peritoneum, plus the muscle and connective tissue of the gut.
- Pleuropericardial folds: fibrous pericardium.
- Pleuroperitoneal membranes: part of the diaphragm.
- Double layers of peritoneum form the mesenteries that hold the gut.
Clinical notes
- The phrenic nerve runs on the fibrous pericardium because it travelled in the pleuropericardial folds.
- Failure of the pleuroperitoneal membrane to close: congenital diaphragmatic hernia.
- Failure of ventral body wall closure: gastroschisis and ectopia cordis.
Test yourself
Think of the answer, then tap the question to see it.
Which mesoderm layer gives rise to the visceral pleura?
The splanchnic (visceral) layer of lateral plate mesoderm.
What separates the pericardial cavity from the pleural cavities?
The pleuropericardial folds (membranes), which form the fibrous pericardium in the adult.
Why does the phrenic nerve run over the surface of the pericardium?
Because it reaches the diaphragm through the pleuropericardial folds, which become the fibrous pericardium.
Which passage connects the pleural and peritoneal cavities before week 7?
The pericardioperitoneal canal, later closed by the pleuroperitoneal membrane.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- Diaphragm: its four components and its innervation
- Congenital diaphragmatic hernia
- Embryonic folding: head, tail and lateral folds
- Week 3: gastrulation and the trilaminar disc
- Mesenteries, the omental bursa and the spleen
- Omphalocele and gastroschisis
- Lung development: the five stages
Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.
Sources: Congenital diaphragmatic hernia: MedlinePlus Genetics (MedlinePlus, U.S. National Library of Medicine, 2019); Langman's Medical Embryology, 13th ed., ch. 7: The Gut Tube and the Body Cavities (Wolters Kluwer, 2015).
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Representative model, for educational purposes only.