Bone is a hard connective tissue that forms the skeleton. It has an inorganic mineral component made up of calcium salts and an organic collagen matrix. Bone comes in two types - dense cortical bone forming the hard outer shell and spongy cancellous bone on the inside. Bone is constantly remodeled through the actions of bone-forming osteoblasts and bone-resorbing osteoclasts. Diseases like osteoporosis weaken the bones through decreased bone density while Paget's disease involves abnormal bone deposition and resorption.