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

Mesmo no esqueleto adulto, ossos são tecidos ativos continuamente passando por mudanças na arquitetura. Este processo denominado remodelação óssea consiste em fases iguais de reabsorção óssea, a remoção e depósito de novo tecido. Quando as células ósseas maduras, osteócitos, sentem o estresse mecânico, eles sinalizam células para o local do osso, por exemplo, as extremidades do fêmur, que são substituídas a cada seis meses.Durante a reabsorção, um tipo de célula, osteoclastos, agarram-se firmemente à superfície. Secretando enzimas lisossomais e protões de hidrogénio, que podem degradar os componentes orgânicos criando cavidades de erosão enquanto digerem a matriz velha ou danificada. O cálcio também é liberado no sangue e desempenha um papel no ciclo de feedback hormonal.Uma vez que o material é dissolvido, o osteoclasto se autodestrói via apoptose o que impede mais destruição do osso. Para iniciar a reversão, células mononucleares aparecem na superfície em preparação para a próxima etapa. Na fase de formação, os osteoblastos se movem para a cavidade e depositam um osso novo através da ossificação da matriz orgânica conhecida como osteoide.Esta parte inclui fibras de colágeno que contribuem para a estrutura e flexibilidade. Após a síntese da matriz, osteoblastos podem se diferenciar em células de revestimento ósseo achatadas ou ficar enterrados nos ossos como osteócitos.

Crockett, Julie C., Michael J. Rogers, Fraser P. Coxon, Lynne J. Hocking e Miep H. Helfrich. "Remodelação óssea em resumo." J Cell Sci 124, nº 7 (1º de abril de 2011): 991–98. [<a href="https://doi.org/10.1242/jcs.063032">Fonte</a>]

Fierro, F. A., J. A. Nolta e I. E. Adamopoulos. "Revisão concisa: células-tronco em osteoimunologia." Células-tronco (Dayton, Ohio) 35, nº 6 (junho de 2017): 1461–67. [<a href="https://doi.org/10.1002/stem.2625" target="__blank">Fonte</a>]

remodelação Óssea

A remodelação óssea é um processo contínuo e equilibrado de reabsorção óssea por osteoclastos e formação óssea por osteoblastos. Em adultos, ela ajuda a manter a massa óssea e a homeostase de cálcio. Embora o stress mecânico possa estimular a rotatividade como parte do processo normal de manutenção e reparação, várias hormonas também regulam a remodelação óssea.
 
 <h4>Controlo Hormonal da Remodelação Óssea</h4>
 
 A hormona paratiróide (PTH) mantém o controlo homeostático dos níveis de cálcio no sangue regulando a reabsorção óssea. A PTH é libertada das glândulas paratiróides em resposta aos baixos níveis de cálcio no sangue. Ela estimula os osteoblastos a produzir moléculas imunes que promovem a diferenciação das células precursoras em osteoclastos. A ativação dos osteoclastos promove a reabsorção óssea, fazendo com que a matriz óssea mineralizada quebre e liberte cálcio no sangue. Quando os níveis de cálcio no sangue são restaurados, um ciclo de feedback negativo impede a libertação adicional de PTH.
 
 <h4>Osteoporose</h4>
 
 A osteoporose é uma doença na qual a reabsorção óssea excede a formação óssea, resultando na redução da densidade óssea. A osteoporose é mais prevalente nas mulheres, especialmente após a menopausa. Isso deve-se ao papel crítico desempenhado pela hormona sexual feminina—estrogénio—na remodelação óssea. O estrogénio limita a formação de osteoclatos e promove a sua destruição através da apoptose. Isso garante que a formação óssea seja maior do que a reabsorção óssea. No entanto, os níveis de estrogónio diminuem severamente nas mulheres em menopausa. Portanto, a reabsorção óssea supera a sua formação, levando à perda de força óssea e ao aumento do risco de fraturas.

Remodelação Óssea

A remodelação óssea é um processo contínuo e equilibrado de reabsorção óssea por osteoclastos e formação óssea por osteoblastos. Em adultos, ajuda a manter ...

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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

what is the skeletal system?

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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...

skeletal muscle anatomy

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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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