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

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from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

HS-LS1-2

Bone Remodeling

- [Konuşmacı] Yetişkin iskeletinde dahi kemikler, mimaride devamlı değişim geçiren aktif dokulardır.
 Bu süreç, eşit aşamaların kemik rezorbsiyonu, alınması ve yeni dokunun nakli dahil, kemiğin yeniden yapılandırılması olarak adlandırılır.
 Olgunlaşmış kemik hücreleri, osteositler, mekanik stres hissettiklerinde kemiklere hücre sinyallerler, her altı ayda bir değiştirilen uyluk kemiğinin ucu buna örnek olarak gösterilebilir.
Rezorbsiyon sırasında, bir hücre türü olan osteoklastler, sıkıca yüzeye tutunur.
 Lizozom enzimi ve hidrojen protonları salgılayıp organik bileşikleri indirgeyebilir, eskiyi parçalarken aşınma oyukları ya da hasarlı matriks yaratabilirler.
 Ayrıca kalsiyum kana karışır, hormonal geribildirim döngüsünde rol oynar.
Madde çözündükten sonra osteositler apoptoz aracılığıyla kendilerini imha ederler, bu da kemiğin daha fazla zarar görmesini engeller.
 Tersini başlatmak için mononükleer hücreler bir sonraki aşama için hazır şekilde yüzeyde belirir.
 Oluşum evresinde, kemik yapıcı hücreler oyuklara doğru ilerler ve osteoid olarak da bilinen organik matriks osifikasyonu ile yeni bir kemik biriktirir.
Bu kısım esneme ve şekle katkısı olan kolajen lif içerir.
 Matriks sentezinden sonra, kemik yapıcı hücreler, düzleşmiş bone-lining hücrelere ayrılabilir, ya da osteositler olarak kemik içerisine gömülü kalırlar.

Crockett, Julie C., Michael J. Rogers, Fraser P. Coxon, Lynne J. Hocking ve Miep H. Helfrich. "Bir Bakışta Kemik Yeniden Şekillenmesi." J Cell Sci 124, no. 7 (1 Nisan 2011): 991–98. [<a href="https://doi.org/10.1242/jcs.063032">Kaynak</a>]

Fierro, F. A., J. A. Nolta ve I. E. Adamopoulos. "Kısa İnceleme: Osteoimmünolojide Kök Hücreler." Kök Hücreler (Dayton, Ohio) 35, no. 6 (Haziran 2017): 1461–67. [<a href="https://doi.org/10.1002/stem.2625" target="__blank">Kaynak</a>]

kemiğin yeniden biçimlenmesi

Kemik yeniden yapılanması, osteoklastlar tarafından kemik rezorpsiyonu ve osteoblastlar tarafından kemik oluşumu içeren sürekli ve dengeli bir süreçtir. Yetişkinlerde, kemik kütlesinin ve kalsiyum homeostazının korunmasına yardımcı olur. Mekanik stres, normal bakım ve onarım sürecinin bir parçası olarak yeniden yapılanmayı uyarabilirken, bazı hormonlar da kemik yeniden şekillenmesini düzenler.

<h4>Kemik Yeniden Yapılanması Hormonal Kontrolü</h4>

Paratiroid hormonu (PTH), kemik rezorpsiyonunu düzenleyerek kan kalsiyum seviyelerinin homeostatik kontrolünü sağlar. PTH, kandaki düşük kalsiyum seviyelerine yanıt olarak paratiroid bezlerinden salınır. Osteoblastları, prekürsör hücrelerin osteoklastlara farklılaşmasını teşvik eden bağışıklık molekülleri üretmek üzere uyarır. Osteoklastların aktivasyonu kemik rezorpsiyonunu teşvik ederek mineralize kemik matrisinin parçalanmasına ve kalsiyumun kana salınmasına neden olur. Kandaki kalsiyum seviyesi geri yüklendiğinde, negatif geri besleme döngüsü PTH'nin daha fazla salınmasını önler.

<h4>Osteoporoz</h4>

Osteoporoz, kemik erimesinin kemik oluşumuna baskın geldiği, düşük kemik yoğunluğu ile sonuçlanan bir hastalıktır. Osteoporoz kadınlarda, özellikle menopozdan sonra daha yaygındır. Bu durum, kadın seks hormonunun (östrojen) kemik yeniden şekillenmesinde oynadığı kritik rolden kaynaklanmaktadır. Östrojen osteoklastların oluşumunu sınırlar ve apoptoz yoluyla bu hücrelerin yıkımını teşvik eder. Bu, kemik oluşumunun kemik rezorpsiyonundan daha yüksek olmasını sağlar. Bununla birlikte, menopozdaki kadınlarda östrojen seviyeleri ciddi şekilde azalır. Bu nedenle, kemik rezorpsiyonu kemik üretimine baskın gelir, bu da kemik gücü kaybına ve kırık riskinin artmasına neden olur.

Kemiğin Yeniden Biçimlenmesi

Kemiğin yeniden şekillenmesi, osteoklastlar tarafından kemik rezorpsiyonu ve osteoblastlar tarafından kemik oluşumunun sürekli ve dengeli bir sürecidir. Yetişkinlerde, korunmasına yardımcı olur ...

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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...

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cross-bridge cycle

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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.

How Hormones Control Bone Turnover | JoVE K12

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HS-LS1-3

How Hormones Control Bone Turnover

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