The document discusses the human body, beginning with cells as the basic building blocks. Tissues are groups of cells that work together, such as epithelial, connective, muscle and nervous tissues. Organs are made of tissues and work together in organ systems like the musculoskeletal system. The musculoskeletal system combines the skeletal system of bones and joints, which provide structure, movement and protection, with the muscular system of muscles and tendons that allow movement. Bones are kept strong through connective tissue and stored minerals.