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

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Bone Remodeling

Sogar im erwachsenen Skelett sind Knochen aktive Gewebe, die sich ständig in der Struktur verändern.
 Dieser Prozess, der als Knochenumbau bezeichnet wird, besteht aus gleichen Phasen der Knochenresorption, der Entfernung und der Ablagerung von neuem Gewebe.
 Wenn reife Knochenzellen, Osteozyten, mechanischen Stress spüren, signalisieren sie Zellen an der Knochenstelle, zum Beispiel den Femurenden, die alle sechs Monate ausgetauscht werden.
 Während der Resorption haftet ein Zelltyp, Osteoklasten, fest an der Oberfläche.
 Durch die Sekretion von lysosomalen Enzymen und Wasserstoffprotonen können sie die organischen Komponenten abbauen und beim Verdauen der alten oder beschädigten Matrix Erosionshohlräume bilden.
 Calcium wird auch ins Blut abgegeben und spielt eine Rolle in hormonellen Rückkopplungsschleifen.
 Sobald das Material aufgelöst ist, zerstört sich die Osteoklaste durch Apoptose selbst, wodurch eine weitere Zerstörung des Knochens verhindert wird.
 Um die Umkehrung einzuleiten, erscheinen einkernige Zellen auf der Oberfläche, um den nächsten Schritt vorzubereiten.
 In der Entstehungsphase dringen Osteoblasten in den Hohlraum ein und lagern durch die Verknöcherung der als Osteoid bekannten organischen Matrix neuen Knochen ab.
 Dieser Teil enthält Kollagenfasern, die zur Struktur und Flexibilität beitragen.
 Nach der Matrixsynthese können sich Osteoblasten in abgeflachte, knochenauskleidende Zellen differenzieren oder als Osteozyten im Knochen vergraben werden.

Crockett, Julie C., Michael J. Rogers, Fraser P. Coxon, Lynne J. Hocking und Miep H. Helfrich. "Knochenumbau auf einen Blick." J Cell Sci 124, Nr. 7 (1. April 2011): 991–98. [<a href="https://doi.org/10.1242/jcs.063032">Quelltext</a>]

Fierro, F. A., J. A. Nolta und I. E. Adamopoulos. "Concise Review: Stammzellen in der Osteoimmunologie." Stammzellen (Dayton, Ohio) 35, Nr. 6 (Juni 2017): 1461–67. [<a href="https://doi.org/10.1002/stem.2625" target="__blank">Quelle</a>]

knochenumbau

Der Knochenumbau ist ein kontinuierlicher und ausgewogener Prozess der Knochenresorption durch Osteoklasten und der Knochenbildung durch Osteoblasten. Dadurch werden die Knochenmasse und die Kalziumhomöostase im erwachsenen Menschen aufrechterhalten. Während mechanischer Stress diese Umwandlung als Teil des normalen Erhaltungs- und Reparaturprozesses stimulieren kann, wird er auch durch verschiedene Hormone reguliert.
 
 <h4>Hormonelle Steuerung des Knochenumbaus</h4>
 
 Parathyroidhormon (PTH) erhält die homöostatische Kontrolle des Blutkalziumspiegels durch die Regulierung der Knochenresorption aufrecht. PTH wird von den Nebenschilddrüsen als Reaktion auf einen niedrigen Kalziumspiegel in das Blut freigesetzt. Es stimuliert die Osteoblasten zur Produktion von Immunmolekülen, die die Differenzierung von Vorläuferzellen in Osteoklasten fördern. Die Aktivierung der Osteoklasten fördert die Knochenresorption, wodurch die mineralisierte Knochenmatrix abgebaut wird und das Kalzium dann ins Blut freigesetzt wird. Wenn der Kalziumspiegel im Blut wieder hergestellt ist, verhindert eine Rückkopplungsmechanismus die weitere Freisetzung von PTH.
 
 <h4>Die Osteoporose</h4>
 
 Osteoporose ist eine Krankheit, bei der die Knochenresorption die Knochenbildung überwiegt, was zu einer reduzierten Knochendichte führt. Die Osteoporose ist bei Frauen, insbesondere nach der Menopause, stärker ausgeprägt. Dies ist auf die kritische Rolle des weiblichen Geschlechtshormons Östrogen beim Knochenumbau zurückzuführen. Östrogen beschränkt die Bildung von Osteoklasten und fördert ihre Zerstörung durch die Apoptose. Dadurch wird sichergestellt, dass die Knochenbildung höher ist als der Knochenabbau. Bei Frauen in den Wechseljahren nimmt der Östrogenspiegel jedoch stark ab. Daher ist die Knochenresorption schneller als die Knochenbildung, was zu einem Verlust der Knochenfestigkeit und einem erhöhten Bruchrisiko führt.

Knochenumbau

Der Knochenumbau ist ein kontinuierlicher und ausgewogener Prozess der Knochenresorption durch Osteoklasten und der Knochenbildung durch Osteoblasten. Bei Erwachsenen hilft es, ...

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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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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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HS-LS1-3

How Hormones Control Bone Turnover

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