Ruumiinontelon

Ruumiinontelo, also known as a body cavity, refers to any fluid-filled space in a multicellular organism. In vertebrates, these cavities serve to enclose and protect vital organs, facilitate organ movement, and act as cushions against shock. The two main body cavities in vertebrates are the dorsal cavity and the ventral cavity.

The dorsal cavity is located on the posterior side of the body and is further divided into the cranial cavity, which houses the brain, and the vertebral cavity, which encloses the spinal cord. These cavities are protected by the skull and vertebral column, respectively.

The ventral cavity is located on the anterior side of the body and is further subdivided by the diaphragm into the thoracic cavity and the abdominopelvic cavity. The thoracic cavity contains the heart and lungs, protected by the rib cage. The abdominopelvic cavity houses organs of the digestive, excretory, and reproductive systems, including the stomach, intestines, liver, kidneys, bladder, and reproductive organs. The diaphragm acts as a muscular partition separating these two major ventral cavities.

In many invertebrates, body cavities are also present, though their organization and terminology can differ. For instance, coeloms are a type of body cavity found in many bilaterian animals, lined by mesodermal tissue. The presence and structure of body cavities are significant features in the classification and understanding of animal anatomy and evolution.