Bone A bone dating from the Pleistocene Ice Age of an extinct species of elephant. A scanning electronic micrograph of bone at 10,000x magnification. Identifiers TA A02.0.00.000 TH H3.01.00.0.00001 FMA 30317 Anatomical terminology Bone A bone is a rigid organ that constitutes part of the vertebrate skeleton. Bones support and protect the various organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, and enable mobility. Bones come in a variety of shapes and sizes and have a complex internal and external structure. They are lightweight yet strong and hard, and serve multiple functions. Bone tissue (osseous tissue) is a hard tissue, a type of dense connective tissue. It has a honeycomb-like matrix internally, which helps to give the bone rigidity. Bone tissue is made up of different types of bone cells. Osteoblasts and osteocytes are involved in the formation and mineralization of bone; osteoclasts are involved in the resorption of bone tissue. Modified (flattened) osteoblasts become the lining cells that form a protective layer on the bone surface. The mineralised matrix of bone tissue has an organic component of mainly collagen called ossein and an inorganic component of bone mineral made up of various salts. Bone tissue is a mineralized tissue of two types, cortical bone and cancellous bone. Other types of tissue found in bones include bone marrow, endosteum, periosteum, nerves, blood vessels and cartilage. In the human body at birth, there are over 270 bones,  but many of these fuse together during development, leaving a total of 206 separate bones in the adult,  not counting numerous small sesamoid bones. The largest bone in the body is the femur or thigh-bone, and the smallest is the stapes in the middle ear. The Greek word for bone is ὀ στέον ("osteon"), hence the many terms that use it as a prefix – such as osteopathy. Structure Cortical bone Cancellous bone Bone marrow Bone cells Osteoblast Osteocyte Osteoclast Extracellular matrix Deposition Types Terminology Development Function Mechanical Synthetic Metabolic Contents
Remodeling Bone volume Clinical significance Fractures Tumors Cancer Painful conditions Osteoporosis Osteopathic medicine Osteology Other animals Society and culture Additional images See also References Footnotes External links Bone is not uniformly solid, but consists of a flexible matrix (about 30%) and bound minerals (about 70%) which are intricately woven and endlessly remodeled by a group of specialized bone cells. Their unique composition and design allows bones to be relatively hard and strong, while remaining lightweight. Bone matrix is 90 to 95% composed of elastic collagen fibers, also known as ossein,  and the remainder is ground substance.
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- Summer '18
- Botany, Bone marrow, cancellous bone, Cortical bone, bone cells