Name: how hormones control bone turnover
Uploaded: 2025-10-23T11:49:19.000Z
Duration: 1 min 40 s
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Bone Remodeling

- Même dans le squelette adulte,les os sont des tissus actifs,subissant des changements d'architecture continuels. 
Ce processus, appelé restructuration de l'os,consiste en phases égales de résorption de l'os,d'élimination, et de dépôt de nouveau tissu. 
Lorsque les cellules osseuses matures, les ostéocytes,décèlent un stress mécanique,elles le signalent aux cellules sur le site de l'os,ici, les extrémités du fémur,qui sont remplacées tous les six mois. 
Au cours de la résorption, un type de cellule,les ostéoclastes, s'accrochent fermement à la surface. 
En sécrétant des enzymes lysosomauxet des protons d'hydrogène,elles peuvent dégrader les composants organiques,créant des cavités d'érosionpar la digestion de la matrice endommagée. 
Le calcium est alors relâché dans le sang,et joue un rôle dans la boucle de régulation des hormones. 
Une fois le matériel dissout,les ostéoclastes s'autodétruisent par apoptose,ce qui empêche de continuer à détruire l'os. 
Pour initier un renversement,des cellules mononucléaires apparaissent à la surfaceen préparation de l'étape d'après. 
Lors de la phase de formation,les ostéoblastes se déplacent vers la cavitéet dépose du nouvel osgrâce à l'ossification de la matrice organique, l'ostéoïde. 
Cette partie comprend des fibres de collagènequi contribuent à la structure et à la flexibilité. 
Après la synthèse de la matrice,les ostéoblastes peuvent se différencieren cellules aplaties qui recouvrent l'os,ou s'enfoncer dans l'os en tant qu'ostéocytes.

Crockett, Julie C., Michael J. Rogers, Fraser P. Coxon, Lynne J. Hocking et Miep H. Helfrich. « Le remodelage osseux en un coup d’œil. » J Cell Sci 124, no. 7 (1er avril 2011) : 991–98. [<a href="https://doi.org/10.1242/jcs.063032">Source</a>]

Fierro, F. A., J. A. Nolta et I. E. Adamopoulos. « Revue concise : les cellules souches en ostéoimmunologie ». Cellules souches (Dayton, Ohio) 35, n° 6 (juin 2017) : 1461-67. [<a href="https://doi.org/10.1002/stem.2625 » target="__blank">Source</a>]

remodelage osseux

Le remodelage des os est un processus continu et équilibré de résorption osseuse par les ostéoclastes et de formation osseuse par les ostéoblastes. Chez les adultes, il aide à maintenir la masse osseuse et l’homéostasie du calcium. Alors que le stress mécanique peut stimuler un roulement dans le cadre du processus normal d’entretien et de réparation, plusieurs hormones régulent également le remodelage osseux.
 
 <h4>Le contrôle hormonal du remodelage des os</h4>
 
 L’hormone parathyroïdienne (PTH) maintient le contrôle homéostatique des niveaux de calcium dans le sang en régulant la résorption osseuse. La PTH est libérée des glandes parathyroïdes en réponse à de faibles niveaux de calcium dans le sang. Elle stimule les ostéoblastes à produire des molécules immunitaires qui favorisent la différenciation des cellules précurseurs en ostéoclastes. L’activation des ostéoclastes favorise la résorption osseuse, ce qui provoque la rupture de la matrice osseuse minéralisée et la libération de calcium dans le sang. Lorsque les niveaux de calcium dans le sang sont rétablis, une boucle de rétroaction négative empêche la libération de la PTH.
 
 <h4>L’ostéoporose</h4>
 
 L’ostéoporose est une maladie dans laquelle la résorption osseuse dépasse la formation osseuse, ce qui entraîne une diminution de la densité osseuse. L’ostéoporose est plus répandue chez les femmes, surtout après la ménopause. Cela est dû au rôle essentiel joué par l’hormone sexuelle féminine — l’œstrogène — dans le remodelage des os. L’œstrogène limite la formation d’ostéoclastes et favorise leur destruction par l’apoptose. Cela garantit que la formation osseuse est plus élevée que la résorption osseuse. Cependant, les niveaux d'œstrogène diminuent sévèrement chez les femmes ménopausées. Par conséquent, la résorption osseuse dépasse sa création, ce qui entraîne une perte de force osseuse et un risque accru de fractures.

Remodelage osseux

Le remodelage osseux est un processus continu et équilibré de résorption osseuse par les ostéoclastes et de formation osseuse par les ostéoblastes. Chez l’adulte, il aide à maintenir ...

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how hormones control bone turnover

Bone turnover is a continuous process in which old bone is broken down and new bone is built. Osteoclasts carry out bone resorption, and osteoblasts carry out bone formation. In adults, this balanced cycle helps maintain bone mass and calcium homeostasis. Mechanical stress can also stimulate turnover as part of normal maintenance and repair.

Parathyroid hormone, or PTH, helps control blood calcium levels by increasing bone resorption when calcium is low. It is released from the parathyroid glands in response to low calcium in the blood. PTH stimulates osteoblasts to produce immune molecules that promote the differentiation of precursor cells into osteoclasts. Once osteoclasts become active, they break down the mineralized bone matrix and release calcium into the blood. When calcium levels return to normal, a negative-feedback loop reduces further PTH release.

Osteoporosis develops when bone resorption becomes greater than bone formation, which lowers bone density. It is more common in women, especially after menopause. Estrogen, the female sex hormone, helps limit the formation of osteoclasts and also promotes their destruction by apoptosis, or programmed cell death. When estrogen levels drop after menopause, bone resorption can outpace bone creation. This weakens bone strength and raises the risk of fractures.

How Hormones Control Bone Turnover

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bone remodeling

Bone turnover is a continuous process in which old bone is broken down and new bone is built. Osteoclasts carry out bone resorption, and osteoblasts carry out bone formation. In adults, this balanced cycle helps maintain bone mass and calcium homeostasis. Mechanical stress can also stimulate turnover as part of normal maintenance and repair. Parathyroid hormone, or PTH, helps control blood calcium levels by increasing bone resorption when calcium is low. It is released from the parathyroid...

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key terms and concepts

Learn how PTH and estrogen regulate bone turnover, calcium balance, and osteoporosis. Clear high school biology coverage of osteoclasts and osteoblasts.

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How Hormones Control Bone Turnover

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