The structure of the bone Your bone is made up of a dense protective outer layer of compact bone called the cortex, and an inner honeycomb-like network of spongy bone. It is made up of collagen for flexibility and calcium for hardness. Bones protect, support, and produce and store blood cells and minerals. Bone cells play a crucial role in the health of the bone. Cells called osteocytes maintain the bone matrix, whilst osteoblast form new bone and osteoclast breakdown old