Weight bearing activity and stress on bone causes small electrical fields to be generated by the minerals of the bone. This detected by the by the osteoblasts which migrate to lay down new bone in the stressed area. Unstressed bone will decrease in size, microgravity, bed rest. Bones of athletes tend to be bigger than those of non-athletes. Somatomedins act on the osteoprogenitor cells which form the osteoblasts.
Osteoblasts increase growth of long bones at the epiphyseal plate.
Testosterone and estrogen stimulate osteoblast activity and bone synthesis. This results in the closure of the epiphyseal plate and bone growth stops. Hyper-secretion of growth hormone in childhood causes increased length of long bones. The plasma concentration of calcium is closely regulated. Function of cardiac cells very dependent on calcium ions 2.