Osteoporosis, reproductive cycle of osteoblasts and osteoclasts, treatments. View of bone trabeculae of spongy bone (blue). Osteoclasts (yellow) destroy the bone, while osteoblasts (roses) make bone. On the left is the cycle of the osteoclast with, from top to bottom, an osteoclast precursor with RANK receptors, a mature osteoclast destroying the bone, an osteoblast in apoptosis. On the right a preosteoblast, a mature osteoblast makes the RANK-L which will attach to the RANK receptor of the preosteoclast. Estrogen binds to the estrogen receptor of osteoblasts to inhibit osteoclast activity. Top right, a blood vessel and a bowel in sections.