endosquelette

An endosquelette is an internal skeleton that forms the main framework of an organism, providing support, protection and a surface for muscle attachment. It contrasts with an exosquelette, which encases the body from the outside. Endoskeletal systems occur in vertebrates and invertebrates such as echinoderms. In vertebrates, the endoskeleton is primarily made of bone and cartilage and includes the axial skeleton (skull, spine, rib cage) and the appendicular skeleton (limbs and girdles). In echinoderms, the endoskeleton consists of calcareous plates embedded in connective tissue, giving rigidity while allowing growth and regeneration.

Bone tissue is a mineralized connective tissue containing osteocytes in a matrix of collagen and hydroxyapatite. Cartilage provides flexible support and joints. The endoskeleton integrates joints, ligaments and tendons, forming a lever system for movement. In vertebrates, bone marrow within certain bones produces blood cells, and bone also serves as a mineral reservoir. Growth occurs through remodeling of bone and, during development, through endochondral or intramembranous ossification; cartilage may be replaced by bone as the skeleton matures.

Development and evolution: In vertebrates, the endoskeleton develops from mesodermal tissue during embryogenesis; a cartilage model often forms first and is replaced by bone in endochondral ossification, while some bones form directly by intramembranous ossification. The endoskeleton enables larger body sizes, provides protection, and permits diverse locomotor adaptations. Among echinoderms, the mineralized plates grow as part of a mutable connective tissue system that allows rigidity and regeneration. Endoskeletal systems have evolved in multiple animal lineages with notable variation in composition and development.