This combination of collagen and calcium makes bone strong and flexible to withstand stress. More than 99 percent of the body's calcium is contained in the bones and teeth. The remaining one percent is found in the blood. Cortical bone is dense and compact. It forms the outer layer of the bones.
Trabecular bone makes up the interior of bone, and has a spongy, honeycomb-like structure.
Bone Remodeling Throughout life, bone is constantly renewed through a process called remodeling . During resorption, old bone tissue is broken down and removed by special cells called osteoclasts. Once this has been done, bone formation begins and new bone tissue is laid down to replace the old. This task is performed by special cells called osteoblasts. Osteoclast and osteoblast function is regulated by several hormones, such as estrogen in women and testosterone in men, calcitonin, parathyroid hormone, and vitamin D, among others.