The human skeleton starts with 270 bones at birth and reduces to 206 bones by adulthood, consisting of an axial skeleton including the skull, vertebral column, and rib cage, and appendicular skeleton with shoulder and pelvic girdles and limb bones. The skeleton functions to support movement, protect organs, produce blood cells, store minerals, and regulate hormones, and can be affected by diseases like osteoporosis, scoliosis, and arthritis.