Kemik

Kemik, or bone, is a rigid organ that constitutes the major component of the vertebrate skeletal system. It consists of bone tissue embedded in a mineralized matrix, primarily collagen type I and hydroxyapatite calcium phosphate, which give bone its strength and resilience. Bone is organized into cortical (compact) bone on the outside and trabecular (spongy) bone inside, with bone marrow contained in the medullary cavities of certain bones.

Functions include providing structural support, protecting internal organs, enabling movement in conjunction with muscles, storing minerals (notably calcium and phosphate), and serving as a site of hematopoiesis in the marrow. The periosteum covers the outer surface, while the endosteum lines internal cavities, both supplying blood vessels and nerves.

Key cell types are osteoblasts (build bone), osteocytes (maintain bone), and osteoclasts (resorb bone). Bone remodeling— a coupled activity of these cells—maintains strength and mineral balance and enables repair after injury. Development begins in embryogenesis: intramembranous ossification forms some flat bones, while endochondral ossification forms most long bones. Growth plates at the ends of long bones drive lengthening during childhood and adolescence, followed by epiphyseal closure.

Clinically, bones can fracture, and conditions such as osteoporosis, osteoarthritis, and osteomyelitis affect bone structure and function. Diagnosis relies on imaging techniques like X-ray, CT, and MRI, while management includes nutrition (calcium and vitamin D), physical activity, medications influencing bone turnover, and, when needed, surgical intervention.