Bone remodeling

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Bone remodeling (or bone metabolism) is a lifelong process where mature bone tissue is removed from the skeleton (a process called bone resorption) and new bone tissue is formed (a process called ossification or new bone formation). Bone remodeling_sentence_0

These processes also control the reshaping or replacement of bone following injuries like fractures but also micro-damage, which occurs during normal activity. Bone remodeling_sentence_1

Remodeling responds also to functional demands of the mechanical loading. Bone remodeling_sentence_2

In the first year of life, almost 100% of the skeleton is replaced. Bone remodeling_sentence_3

In adults, remodeling proceeds at about 10% per year. Bone remodeling_sentence_4

An imbalance in the regulation of bone remodeling's two sub-processes, bone resorption and bone formation, results in many metabolic bone diseases, such as osteoporosis. Bone remodeling_sentence_5

Physiology Bone remodeling_section_0

Bone homeostasis involves multiple but coordinated cellular and molecular events. Bone remodeling_sentence_6

Two main types of cells are responsible for bone metabolism: osteoblasts (which secrete new bone), and osteoclasts (which break bone down). Bone remodeling_sentence_7

The structure of bones as well as adequate supply of calcium requires close cooperation between these two cell types and other cell populations present at the bone remodeling sites (eg. immune cells). Bone remodeling_sentence_8

Bone metabolism relies on complex signaling pathways and control mechanisms to achieve proper rates of growth and differentiation. Bone remodeling_sentence_9

These controls include the action of several hormones, including parathyroid hormone (PTH), vitamin D, growth hormone, steroids, and calcitonin, as well as several bone marrow-derived membrane and soluble cytokines and growth factors (ex. Bone remodeling_sentence_10

M-CSF, RANKL, VEGF, IL-6 family...). Bone remodeling_sentence_11

It is in this way that the body is able to maintain proper levels of calcium required for physiological processes. Bone remodeling_sentence_12

Thus bone remodeling is not just occasional "repair of bone damage" but rather an active, continual process that is always happening in a healthy body. Bone remodeling_sentence_13

Subsequent to appropriate signaling, osteoclasts move to resorb the surface of the bone, followed by deposition of bone by osteoblasts. Bone remodeling_sentence_14

Together, the cells that are responsible for bone remodeling are known as the basic multicellular unit (BMU), and the temporal duration (i.e. lifespan) of the BMU is referred to as the bone remodeling period. Bone remodeling_sentence_15

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: remodeling.