The skeletal system has 6 main functions including providing support and protecting internal organs. Bone is made up of water, organic proteins, and mineral salts. It is constantly remodeling and made of two main tissues, bone and cartilage. The skeletal system contains long bones, flat bones, and irregular bones that each have specific structures like compact and spongy bone. Bone growth and repair are complex processes involving cells like osteoblasts and osteoclasts. Calcium levels, hormones, and mechanical forces all influence bone metabolism and aging affects bone density and strength.