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The coelom is the mesodermally lined cavity between the gut and the outer body wall. During the development of the embryo, coelom formation begins in the gastrulation stage. The developing digestive tube of an embryo forms as a blind pouch called the archenteron. In protostomes, the coelom forms by a process known as schizocoely. [6]
Organs formed inside the coelom can freely move, grow, and develop independently of the body wall while fluid in the peritoneum cushions and protects them from shocks. Arthropods and most molluscs have a reduced (but still true) coelom, the hemocoel (of an open circulatory system) and the smaller gonocoel (a cavity that contains the gonads).
The resulting cavity between the somatopleure and splanchnopleure is called the intraembryonic coelom. This space will give rise to the thoracic and abdominal cavities. The coelomic spaces in the lateral mesoderm and cardiogenic area are isolated. The isolated coelom begins to organize into a horseshoe shape. The spaces soon join together and ...
This forms the viscera and heart; forms a dorsal layer associated with ectoderm, the somatopleuric mesoderm. This forms the body wall lining and dermis. Abdominal portion becomes contained in dorsal mesentery, part of the serosal mesoderm. When the two layers form, a cardiogenic plate is visible.
The mesothelium is a membrane composed of simple squamous epithelial cells of mesodermal origin, [2] which forms the lining of several body cavities: the pleura (pleural cavity around the lungs), peritoneum (abdominopelvic cavity including the mesentery, omenta, falciform ligament and the perimetrium) and pericardium (around the heart).
In the anatomy of an embryo, the splanchnopleuric mesenchyme is a structure created during embryogenesis when the lateral mesodermal germ layer splits into two layers. The inner (or splanchnic) layer adheres to the endoderm, and with it forms the splanchnopleure (mesoderm external to the coelom plus the endoderm).
A portion of the amniogenic somatopleure adjacent to the base of the head fold is identified as the region contributing to embryonic tissues in the thoracic wall and pharyngeal and cardiac regions. The somatopleure is known to serve as the matrix of the ventrolateral body wall and gives rise to connective tissue, tendons and the sternum. [2] [3]
A serous membrane lines the pericardial cavity of the heart, and reflects back to cover the heart, much like an under-inflated balloon would form two layers surrounding a fist. Called the pericardium, this serous membrane is a two-layered sac that surrounds the entire heart except where blood vessels emerge on the heart's superior side; [4]