ossa

Ossa is the Latin plural for os, a term used in anatomy to denote bones. In modern medical and anatomical language, ossa appears in names such as ossa cranii (the bones of the skull) or ossa membri. The English term bones is more commonly used, but ossa remains a 흔 historically used plural.

Bones are living, dynamic tissues that form the rigid framework of vertebrate skeletons. They consist of a mineralized matrix with two main tissue types: compact (cortical) bone, which is dense and forms the outer layer, and cancellous (trabecular) bone, with a porous, lattice-like structure inside. The bone matrix contains collagen type I fibers reinforced by mineral deposits of hydroxyapatite, giving strength and resilience. Bone houses cells such as osteocytes (within lacunae), osteoblasts (bone-forming), osteoclasts (bone-resorbing), and progenitor cells, all enclosed by a fibrous periosteum on the outer surface and an endosteum lining internal cavities.

Ossa develop and grow through two main ossification processes: intramembranous ossification, forming flat bones like those of the skull, and endochondral ossification, forming most other bones from cartilage models. Long bones grow in length at growth plates (epiphyseal plates) during childhood and adolescence and remodel throughout life, balancing formation and resorption in response to mechanical load and metabolic needs.

Bones are classified by shape into long, short, flat, irregular, sutural, and sesamoid categories. They function to provide support, protect organs, enable movement with muscles, store minerals (notably calcium and phosphate), and house bone marrow for hematopoiesis. Pathologies such as fractures and osteoporosis illustrate the clinical importance of ossa in health and disease.