Bones Skeletal System

About the Bones Skeletal System

The adult skeleton has 206 bones: 80 axial skull, vertebral column, ribs, sternum and 126 appendicular limbs, girdles. Bone types include long femur, humerus, short carpals, tarsals, flat skull, scapula, ribs, and irregular vertebrae. Long bone structure includes diaphysis shaft, epiphyses ends, metaphysis growth zone, epiphyseal plate growth plate, medullary cavity with yellow marrow, and articular cartilage. Bone tissue is 35 percent organic collagen type I providing tensile strength and 65 percent inorganic hydroxyapatite calcium phosphate providing compressive strength. Osteoblasts build bone, osteoclasts resorb bone, and osteocytes maintain bone. Bone remodeling is continuous, replacing approximately 10 percent of the skeleton annually. The hematopoietic red marrow in flat bones, vertebrae, and proximal femur and humerus produces all blood cells. The skeleton stores 99 percent of body calcium and 85 percent of phosphate. Wolff law states bone adapts to mechanical loading. Osteoporosis reduces bone mass, increasing fracture risk. Major bones include the femur longest and strongest, stapes smallest in middle ear, and pelvis protecting pelvic organs.