Osteoclast cells

FIGURE 10.17 Proton pumps cluster on the ruffled border of osteoclast cells and function to pump protons into the space between the cell membrane and the bone surface. High proton concentration in this space dissolves the mineral matrix of the bone. 

Bone metabolism comprises the processes of bone formation and bone resorption, the key actions by which skeletal mass, structure and quality are accrued and maintained throughout life. In the mature skeleton, anabolic and catabolic actions are mostly balanced due to the tight regulation of the activity of bone forming ( osteoblast) and bone resorbing ( osteoclast) cells through circulating osteotropic hormones and locally active cytokines. 

Bone maintenance during adulthood is dependent on the equilibrium between bone formation by osteoblast cells and bone resorption by osteoclast cells. Bone loss with age is linked to increased osteoclast activity compared to... 

Osteoclasts Cells responsible for bone resorption during the... 

Osteoclast cells generally require an apatitic substrate (dentine, enamel, bone slices or synthetic apatite coatings) to attach to and act on and the effect of fluoride ions in solution cannot be readily distinguished from the effect of fluoride on... 

Only a very few experiments have been published concerning the behaviour of osteoclast cells on fluoridated biomaterial surfaces, although this point seems crucial concerning the mode of action of osteoclast cells. Most studies report on the effect of fluoride ions in the solution, which may also change the surface on which these cells are cultivated. Ramaswamy et al. [191] have shown that osteoclasts attach to FA ceramic surfaces but that the resorption pits were barely observed. It is accepted that due to the very slow solubility of fluorapatite... 

Wiebe SH, Sims SM, Dixon SJ. 1999. Calcium signalling via multiple P2 purinoceptor subtypes in rat osteoclasts. Cell Physiol Biochem 9 323-37. 

Nakagawa H, Wachi M, Woo J-T, Kato M, Kasai S, Takahashi F, Fee I-S, Naga K. Fenton reaction is primarily involved in a mechanism of (—)-epigal-locatechin-3-gallate to induce osteoclastic cell death. Biochem Biophys Res Commun 2002 292 94-101. 

FUNCTION Decreases plasma calcium. Acts on bone by decreasing the activity of osteoclasts (cells that break down bone). Its net effect is opposite to that of parathyroid hormone. 

FUNCTION Maintains the level of calcium in the blood, acting mainly on bone and kidney. In bone, PTH stimulates osteoclast cells to produce bone breakdown with release of calcium and phosphorus (PTH has a similar effect in this regard as vitamin D, but operates by a different mechanism PTH acts through cyclic AMP). In the kidney, PTH increases calcium reabsorption and phosphate excretion (vitamin D, however, increases absorption of both calcium and phosphorus in the kidney). 

V. CROSS-LINKAGE OF COLLAGEN CONTROL OF RESORPTION BY OSTEOCLASTIC CELLS... 

The results of animal tests using rats, rabbits, and dogs have demonstrated high biocompatibility and high osteoconductivity. Moreover, the most impressive bone tissue reaction of the HAp/Col composites is incorporation of the composites into the bone-remodeling process, that is, they are resorbed by osteoclastic cells. ... 

Osteoclastic cells are the same cells as osteoclasts, but they are artificial cells that resorb bone. Therefore the cells that resorb the HAp/Col composites are not osteoclasts if one uses the histologic terminology correctly. 

Bone is a vital, dynamic connective tissue which has evolved to reflect a balance between its two major functions, provision of mechanical integrity for locomotion and protection and involvement in the metabolic pathways associated with mineral homeostatis. In addition, bone is the primary site of hemopoiesis and recent findings support its important role as a component of the immune system [1]. Bones continuously mend and rebuild themselves by opposing actions of two types of cells, the osteoblasts that form bone and the osteoclasts that resorb (destroy) bone. When the activity of the bone destroying osteoclast cell outpaces that of bone forming osteoblasts, the bottom line is bone loss and the result is osteoporosis. 

Bone tissue also contains osteoclasts, which are multinucleated cells that are derived from the hematopoietic (granulocyte-monocyte) cell line located in bone marrow. Osteoclasts are primarily responsible for bone resorption and they secrete enzymes and hydrochloric acid that break down collagen matrix and help dissolve the bone. The area where osteoclast cell membrane lies adjacent to bony tissue is known as a Howship s lacunae. The osteoclast cell membrane that lies in close proximity to bone can contain numerous villous extensions and form a ruffled border. These areas are also known as resorption pits. The plasmalemma border of the osteoclast cell in this region forms a specialized seal with the underlying bone to prevent the release of enzymes and hydrochloric acid. This process also results in the release of growth factors previously deposited in bone by osteoblasts, which are responsible for maintaining the process of regenerating new bone. 

Osteoporosis is a different disease. It can be ttiought of as osteoclast cells removing calcium more quickly that osteoblast cells car lay calcium down The result is porous, brittle bones that break easily. At one time calcitonin some-limes was prescribed to decrease the release of caldum from bone by osteoclast cells. In addition to the bisphosphonates and impact exercise, Lum with D vitamins is currently recom-bended to replace calcium being released from me and excreted through the kidney. 

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