Normal Bone Tissue Bone is the supporting framework of the body. Most bones are hollow. The outer part of bones consists of a network of fibrous tissue called matrix onto which calcium salts are deposited. At each end of the bone is a zone of cartilage, a softer form of bone-like tissue. Cartilage is made of a fibrous tissue matrix mixed with a gel-like substance. Unlike bone, cartilage does not contain much calcium. Cartilage acts as a cushion between bones and, together with ligaments and some other tissues, forms the joints between bones. The bone itself is very hard and strong. Some bone is able to support as much as 12,000 pounds per square inch. It takes as much as 1,200 to 1,800 pounds of pressure to break a femur (thigh bone). The outside of the bone is covered with a layer of fibrous tissue called periosteum. The bone itself contains 2 kinds of cells. The osteoblast is the cell responsible for forming bone, and the osteoclast is the cell responsible for dissolving bone. Although bone looks to be a very unchanging organ, the truth is that it is very active. New bone is constantly forming, and at the same time, old bone is dissolving. Bone marrow is the soft tissue inside the hollow bones. The marrow of some bones consists only of fatty tissue. The marrow of other bones is a mixture of fat cells and blood-forming (hematopoietic) cells. These blood-forming cells produce red blood cells, white blood cells, and blood platelets. There are some other cells in the marrow such as plasma cells, fibroblasts, and reticuloendothelial cells. All these tissues can develop into a cancer.

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