Coelom

With coelom (Greek coiloma depression, cavity, also coelom ) is called the secondary body cavity of many animals, such as the chordates, or annelids. It is a fluid-filled cavity, which is surrounded by a mesodermal epithelium and as a liquid cushion in many protostomes takes over the function of a hydraulic skeleton.

For a number of animal groups, the coelom is reduced and only incompletely preserved as a residual. For molluscs it still exists in the form of the pericardium and the Gonadenhöhle in arthropods it is passed into a Mixocoel, where also still significant remains are preserved (for example, as a sheath of Metanephridien, called Nephrocoel ).

The coelom is during ontogenesis by folding from the primitive gut ( archenteron ) or made ​​of special, the endoderm, mesoderm cells entstamme ends a little later and displaces the segmentation cavity resulting from the primary body cavity, often completely.

In mammals arising from the coelom the chest cavity, the abdominal cavity and the pericardium cavity. The coelomic epithelium is the tunica serosa ( pleura, peritoneum ).

A distinction acoelomate, pseudocoelomate, coelomate and mixocoelomate organization.

Acoelomate organization

There is no uniform extracellular cavity. Between the basal matrix of the epidermis and that of the intestine and the internal organs of the body only with connective tissue ( mesenchyme, " parenchyma " ) and connective tissue muscles is required. Mesenchymatisches tissue fills the space between the derivatives of ectoderm and endoderm from completely, possibly intercellular spaces form a Schizozoel. The primary body cavity is restricted to the extracellular matrix between the mesodermal cells. The digestive tract, the ontogenetically derived from Gastralraum, is the only continuous body cavity.

Pseudocoelomate organization

The mesodermal cell aggregates take the space between ectoderm and endoderm formation is not completely one, the primary body cavity is maintained even adult and may even lead to shape-determining body cavity ( Pseudocoel ) are. The primary body cavity is extended as a fluid-filled cavity between the body wall and intestine. A cavity between epidermis and intestine is present but not lined by epithelium own.

Coelomate organization

The primary body cavity is concentrated by the secondary body cavity to the space between the Coelothelien or between Coelothelien and body or intestinal wall. The coelom is delimited by a true epithelium. It displaces more or less completely the primary body cavity, the rest are only present in blood vessels.

Mixocoelomate organization

Embryonal be applied Mesodermalstreifen and Coelomsäckchen, in consequence but the Coelomwände the formation of various organ systems are resolved (eg muscles). This results in the fusion of primary and secondary body cavity, the cavity thus created is called Mixocoel ( hemocoel ). This is made possible by the chitin cuticle, which makes the hydro skeleton function adopted the Coelomräume superfluous. As a result of Mixocoelbildung an open circulatory system with a uniform fluid, the hemolymph was born.