Body Cavities 

A body cavity can be defined as the space that remains after the organs in­side it are removed, but this definition does not do justice to the variety and factions of body cavities. Humans have four body cavities: (1) the dorsal body cavity that encloses the brain and spinal cord; (2) the thoracic cavity that encloses the heart and lungs; (3) the abdominal cavity that encloses most of the digestive organs and kidneys; and (4) the pelvic cavity that encloses cranial related to the bladder and reproductive organs. The cranial cavity cushions and pro­tects the brain within a rigid skull. The other body cavities also cushion in ternal organs, but instead of being rigid, they have to be flexible for the heart, lungs, digestive organs, and reproductive organs to expand.

Schematic diagrams of the bodies of animals with coeloms, with pseudocoeloms, or without body captives.

In humans all but the cranial cavity develop from the coelom (pro­nounced SEE-lum). A coelom is a cavity that is entirely enclosed within cells derived from the middle layer of embryonic tissue. A few groups of animals, such as roundworms (Nematoda), have a body cavity that is only partly en­closed by tissue from the middle layer. Such a body cavity is called a pseudo­coelom (pronounced SOO-doe-SEE-lum). In a few other groups, such as flatworms (Platyhelminthes), there is no body cavity.

References

Pechenik, Jan A. “Classification by Developmental Pattern.” In Biology of the Inverte­brates, 4th ed. Boston: McGraw-Hill Higher Education, 2000.

Saladin, Kenneth S. “Body Cavities and Membranes.” In Anatomy and Physiology. Boston: McGraw-Hill, 1998.