The positioning of this "sealing zone" appears to be mediated by integrins expressed on the osteoclast surface. With the sealing zone in place, the multinucleated osteoclast reorganizes itself. Developing the highly invaginated ruffled membrane apposing the resorption compartment allows massive secretory activity. In addition, it permits the vesicular transcytosis of the mineral and degraded collagen from the ruffled border to the free membrane of the cell, and its release into the extracellular compartment. This activity completes the bone resorption, and both the mineral components and collagen fragments are released to the general circulation. Regulation
Osteoclasts are regulated by several hormones, including parathyroid hormone (PTH) from the parathyroid gland, calcitonin from the thyroid gland,  and growth factor interleukin 6 (IL-6). This last hormone, IL-6, is one of the factors in the disease osteoporosis. Osteoporosis occurs when there is an imbalance between the bone resorption activities of osteoclasts and the bone formation activities of osteoblasts.Osteoclast activity is also mediated by the interaction of two molecules produced by osteoblasts, namely osteoprotegerin and RANK ligand. Note that these molecules also regulate differentiation of the osteoclast. Odontoclast
An odontoclast (/odon·to·clast/; o-don´to-klast) is an osteoclast associated with absorption of the roots of deciduous teeth. Alternate use of term
An osteoclast can also be an instrument used to fracture and reset bones (the origin is Greek osteon: bone and klastos: broken). To avoid confusion, the cell was originally termed osotoclast. When the surgical instrument went out of use, the cell became known by its present name.
Mutations in the cathepsin K gene are associated with pycnodysostosis, a hereditary osteopetrotic disease, characterised by a lack of functional cathepsin K expression. Knockout studies of cathepsin K in mice lead to an osteopetrotic phenotype, which, is partially compensated by increased expression of proteases other that cathepsin K and enhanced osteoclastogenesis. Cathepsin K has an optimal enzymatic activity in acidic conditions. It is synthesized as a proenzyme with a molecular weight of 37kDa, and upon activation by autocatalytic cleavage, is transformed into the mature, active form with a molecular weight of ~27kDa. Upon polarization of the osteoclast over the site of resorption, cathepsin K is secreted from the ruffled border into the resorptive pit. Cathepsin K transmigrates across the ruffled border by intercellular vesicles and is then released by the functional secretory domain. Within these intercellular vesicles, cathepsin K, along with reactive oxygen species generated by TRAP, further degrades the bone extracellular matrix. Several other cathepsins are expressed in osteoclasts including cathepsins B, C, D, E, G, and L.  The function of these cysteine and aspartic proteases is generally unknown within bone, and they are expressed at much lower levels than cathepsin K.
Studies on cathepsin L knockout mice have been mixed, with a report of reduced trabecular bone in homozygous and heterozygous cathepsin L knockout mice compared to wild-type and another report finding no skeletal abnormalities. Matrix metalloproteinases
The matrix metalloproteinases (MMPs) comprise a family of more than 20 zinc-dependent endopeptidases.