Development of Body Cavities Flashcards
What is the intraembryonic coelom, and how is it formed?
The intraembryonic coelom is a cavity formed within the lateral plate mesoderm during embryogenesis. It arises from cavitation in the lateral mesoderm and splits the mesoderm into somatic (parietal) and splanchnic (visceral) layers.
What are the three main parts of the intraembryonic coelom?
Pericardial cavity (horseshoe-shaped initially).
Peritoneal cavity (caudal part).
Pericardio-peritoneal canals (connect cranial and caudal parts).
What role does the septum transversum play in development?
The septum transversum is a thick mesodermal plate that partially separates the thoracic and abdominal cavities. It contributes to the central tendon of the diaphragm and is initially located opposite cervical somites (C3-C5).
How do the pleuropericardial folds form, and what is their function?
The pleuropericardial folds arise as ridges of mesenchyme in the pericardioperitoneal canals. They grow medially to partition the thoracic cavity into two pleural cavities (lateral) and one pericardial cavity (central), forming the fibrous pericardium.
What structures contribute to the formation of the diaphragm?
Septum transversum (central tendon).
Pleuroperitoneal membranes (close canals).
Dorsal mesentery of the esophagus (crura).
Body wall mesoderm (peripheral musculature).
Myoblasts from cervical somites (C3-C5) (innervation via phrenic nerve).
What is congenital diaphragmatic hernia (CDH), and why is it more common on the left?
CDH occurs due to failure of the pleuroperitoneal membrane to fuse, allowing abdominal organs to herniate into the pleural cavity. The left side is more affected because it closes later than the right.
What is the embryological cause of gastrochisis?
Gastrochisis results from incomplete lateral folding of the embryo, causing a full-thickness defect in the anterior abdominal wall (often right-sided) and herniation of intestines outside the body.
How does the phrenic nerve become associated with the diaphragm?
Myoblasts from cervical somites (C3-C5) migrate into the septum transversum during development, bringing their nerve fibers (phrenic nerve) to innervate the diaphragm.
What are the pleuroperitoneal membranes, and what is their role?
Paired membranes that grow from the posterior body wall to close the pericardioperitoneal canals, separating the pleural and peritoneal cavities. They fuse with the septum transversum and esophageal mesentery.
How does the pericardial cavity change position during embryogenesis?
Cephalocaudal folding moves the pericardial cavity ventrally, while lateral folding incorporates it into the thorax. The pleuropericardial folds later isolate it from the pleural cavities.
What is the role of the lateral plate mesoderm in body cavity development?
The lateral plate mesoderm splits into two layers:
Somatic (parietal) mesoderm: Forms the body wall.
Splanchnic (visceral) mesoderm: Forms the gut wall. The space between them becomes the intraembryonic coelom.
How does the intraembryonic coelom communicate with the extraembryonic coelom?
The intraembryonic coelom communicates with the extraembryonic coelom (chorionic cavity) around the region of the secondary yolk sac during early development.
What causes the formation of a single peritoneal cavity?
Lateral folding of the embryo causes the caudal parts of the intraembryonic coelom to merge, forming a single peritoneal cavity.
What structures are contained within the pleuropericardial folds?
Common cardinal veins (drain into the sinus venosus).
Phrenic nerve (innervates the diaphragm).
Why does the right pleuropericardial canal close before the left?
The right common cardinal vein is larger, creating a bigger pleuropericardial fold that fuses earlier. The left vein diminishes in size, delaying closure.
: What is the definitive diaphragm’s embryological origin?
Septum transversum (central tendon).
Pleuroperitoneal membranes (posterolateral parts).
Esophageal mesentery (crura).
Body wall mesoderm (peripheral muscle).
What is the positional change of the septum transversum during development?
Initially opposite cervical somites (C3-C5), it descends to thoracic levels (T6-T11) as the embryo grows, pulling the phrenic nerve with it.
What is an esophageal hiatal hernia, and what causes it?
Protrusion of the stomach into the thorax due to an enlarged esophageal hiatus. Causes include a short esophagus or weak diaphragmatic musculature.
How do the pericardioperitoneal canals contribute to thoracic cavity development?
They initially connect the pericardial and peritoneal cavities but are later partitioned by the pleuropericardial and pleuroperitoneal folds into pleural cavities.
What is the clinical significance of pulmonary hypoplasia in congenital diaphragmatic hernia (CDH)?
Herniated abdominal organs compress the developing lungs, impairing their growth and leading to life-threatening respiratory insufficiency after birth.
How does the fibrous pericardium form?
It develops from fused pleuropericardial membranes, which are drawn into place by the expanding lungs and descending heart.
What is the role of the dorsal mesentery of the esophagus in diaphragm formation?
It contributes to the crura of the diaphragm and helps anchor the esophagus during development.
Why is gastrochisis more common on the right side?
The right lateral body wall closes later than the left, increasing the likelihood of incomplete fusion and herniation.
What structures are derived from somatic vs. splanchnic mesoderm?
Somatic: Body wall (parietal serosa, connective tissue).
Splanchnic: Gut wall (visceral muscle, connective tissue).
