The backbone vertebrae, skull, and rib cage make up the _______ skeleton. Among other types of cells, bone marrow produces _______ blood cells, which carry oxygen in the blood. _______ can eventually become osteocytes. If bones rapidly deconstruct faster than new bone tissue grows, this can lead to less dense and more fragile bones. When severe, this condition is called _______. _______ such as the MCL and ACL connect bone to other bone at joints.