Bone resorption

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Bone resorption_table_infobox_0

Bone ReabsorptionBone resorption_header_cell_0_0_0
SpecialtyBone resorption_header_cell_0_1_0 Rheumatology Q4941581?uselang=en#P1995Bone resorption_cell_0_1_1

Bone resorption is resorption of bone tissue, that is, the process by which osteoclasts break down the tissue in bones and release the minerals, resulting in a transfer of calcium from bone tissue to the blood. Bone resorption_sentence_0

The osteoclasts are multi-nucleated cells that contain numerous mitochondria and lysosomes. Bone resorption_sentence_1

These are the cells responsible for the resorption of bone. Bone resorption_sentence_2

Osteoclasts are generally present on the outer layer of bone, just beneath the periosteum. Bone resorption_sentence_3

Attachment of the osteoclast to the osteon begins the process. Bone resorption_sentence_4

The osteoclast then induces an infolding of its cell membrane and secretes collagenase and other enzymes important in the resorption process. Bone resorption_sentence_5

High levels of calcium, magnesium, phosphate and products of collagen will be released into the extracellular fluid as the osteoclasts tunnel into the mineralized bone. Bone resorption_sentence_6

Osteoclasts are prominent in the tissue destruction found in psoriatic arthritis and rheumatological disorders. Bone resorption_sentence_7

The human body is in a constant state of bone remodeling. Bone resorption_sentence_8

Bone remodelling is a process which maintains bone strength and ion homeostasis by replacing discrete parts of old bone with newly synthesized packets of proteinaceous matrix. Bone resorption_sentence_9

Bone is resorbed by osteoclasts, and is deposited by osteoblasts in a process called ossification. Bone resorption_sentence_10

Osteocyte activity plays a key role in this process. Bone resorption_sentence_11

Conditions that result in a decrease in bone mass can either be caused by an increase in resorption or by a decrease in ossification. Bone resorption_sentence_12

During childhood, bone formation exceeds resorption. Bone resorption_sentence_13

As the aging process occurs, resorption exceeds formation. Bone resorption_sentence_14

Bone resorption rates are much higher in post-menopausal older women due to estrogen deficiency related with menopause. Bone resorption_sentence_15

Common treatments include drugs that increase bone mineral density. Bone resorption_sentence_16

Bisphosphonates, RANKL inhibitors, SERMs—selective oestrogen receptor modulators, hormone replacement therapy and calcitonin are some of the common treatments. Bone resorption_sentence_17

Light weight bearing exercise tends to eliminate the negative effects of bone resorption. Bone resorption_sentence_18

Regulation Bone resorption_section_0

Bone resorption is highly stimulated or inhibited by signals from other parts of the body, depending on the demand for calcium. Bone resorption_sentence_19

Calcium-sensing membrane receptors in the parathyroid gland monitor calcium levels in the extracellular fluid. Bone resorption_sentence_20

Low levels of calcium stimulates the release of parathyroid hormone (PTH) from chief cells of the parathyroid gland. Bone resorption_sentence_21

In addition to its effects on kidney and intestine, PTH increases the number and activity of osteoclasts. Bone resorption_sentence_22

The increase in activity of already existing osteoclasts is the initial effect of PTH, and begins in minutes and increases over a few hours. Bone resorption_sentence_23

Continued elevation of PTH levels increases the abundance of osteoclasts. Bone resorption_sentence_24

This leads to a greater resorption of calcium and phosphate ions. Bone resorption_sentence_25

High levels of calcium in the blood, on the other hand, leads to decreased PTH release from the parathyroid gland, decreasing the number and activity of osteoclasts, resulting in less bone resorption. Bone resorption_sentence_26

Vitamin D increases absorption of calcium and phosphate in the intestinal tract, leading to elevated levels of plasma calcium, and thus lower bone resorption. Bone resorption_sentence_27

Calcitriol (1,25-dihydroxycholecalciferol) is the active form of vitamin D3. Bone resorption_sentence_28

It has numerous functions involved in blood calcium levels. Bone resorption_sentence_29

Recent research indicates that calcitriol leads to a reduction in osteoclast formation, and bone resorption. Bone resorption_sentence_30

It follows that an increase in vitamin D3 intake should lead to a decrease in bone resorption — it has been shown that oral administration of vitamin D does not linearly correlate to increased serum levels of calcifediol, the precursor to calcitriol. Bone resorption_sentence_31

Calcitonin is a hormone secreted by the thyroid in humans. Bone resorption_sentence_32

Calcitonin decreases osteoclast activity, and decreases the formation of new osteoclasts, resulting in decreased resorption. Bone resorption_sentence_33

Calcitonin has a greater effect in young children than in adults, and plays a smaller role in bone remodeling than PTH. Bone resorption_sentence_34

In some cases where bone resorption outpaces ossification, the bone is broken down much faster than it can be renewed. Bone resorption_sentence_35

The bone becomes more porous and fragile, exposing people to the risk of fractures. Bone resorption_sentence_36

Depending on where in the body bone resorption occurs, additional problems like tooth loss can arise. Bone resorption_sentence_37

This can be caused by conditions such as hyperparathyroidism and hypovitaminosis D or even decreased hormonal production in the elderly. Bone resorption_sentence_38

Some diseases with symptoms of decreased bone density are osteoporosis, and rickets. Bone resorption_sentence_39

Some people who experience increased bone resorption and decreased bone formation are astronauts. Bone resorption_sentence_40

Due to the condition of being in a zero-gravity environment, astronauts do not need to work their musculoskeletal system as hard as when on earth. Bone resorption_sentence_41

Ossification decreases due to a lack of stress, while resorption increases, leading to a net decrease in bone density. Bone resorption_sentence_42

Alcoholism Bone resorption_section_1

The effects of alcohol on bone mineral density (BMD) are well-known and well-studied in animal and human populations. Bone resorption_sentence_43

Through direct and indirect pathways, prolonged ethanol exposure increases fracture risk by decreasing bone mineral density and promoting osteoporosis. Bone resorption_sentence_44

Indirect effects of alcohol abuse occur via growth hormone, sex steroids, and oxidative stress. Bone resorption_sentence_45

Growth hormone is an important regulator of bone growth and remodeling in adults, and it acts via insulin-like growth factor I (IGF1) to stimulate osteoblastic differentiation. Bone resorption_sentence_46

Chronic alcoholism decreases the levels of IGF1, which suppresses the ability of GH to increase bone mineral density. Bone resorption_sentence_47

Increasing alcohol consumption is linked with decreasing testosterone and serum estradiol levels, which in turn lead to the activation of RANK (a TNF receptor) protein that promote osteoclast formation. Bone resorption_sentence_48

Oxidative stress results when ethanol induces NOX expression, resulting in ROS production in osteoblasts which can ultimately result in cell senescence. Bone resorption_sentence_49

Direct effects of chronic alcoholism are apparent in osteoblasts, osteoclasts and osteocytes. Bone resorption_sentence_50

Ethanol suppresses the activity and differentiation of osteoblasts. Bone resorption_sentence_51

At the same time, it has a direct effect on osteoclast activity. Bone resorption_sentence_52

This results in an increased bone resorption rate and a decreased bone mineral density due to increased pit numbers and pit areas in the bone. Bone resorption_sentence_53

Research has shown that viable osteocytes (another type of bone cell) may prevent osteoclastogenesis, whereas apoptotic osteocytes tend to induce osteoclast stimulation. Bone resorption_sentence_54

Stimulation of osteocyte apoptosis by alcohol exposure may explain decreased bone mineral density in chronic drinkers. Bone resorption_sentence_55

See also Bone resorption_section_2

Bone resorption_unordered_list_0


Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Bone resorption.