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

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Life Science

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

From Molecules to Organisms: Structures and Processes

HS-LS1-2

Bone Remodeling

成人の骨格であっても 骨は活性組織であり 構造の変化を続けています。骨再形成と呼ばれるこのプロセスは 骨の再吸収、除去、沈着といった 等しい3つの段階から成ります。成熟した骨細胞が機械的ストレスを感じると 細胞を骨部位に伝えます。例えば、大腿骨端は 6ヶ月ごとに置換されます。再吸収のプロセスでは細胞の1種である破骨細胞が 表面にしっかりと付着します。リソソーム酵素とプロトンを分泌して 有機分を分解し 古い、または損傷したマトリクスを消化するため 侵食して空洞を作ります。カルシウムもまた血中に放出され ホルモンのフィードバック・ループにおいて重要な役割をします。骨が溶解したら 破骨細胞は骨がさらに破壊しないように アポトーシスによって自己破壊します。反転の開始には 次の段階に備えて 表面に単核細胞が現れます。形成段階では、骨芽細胞が空洞に移動し 類骨として知られる有機マトリックスの骨化を介して 新しい骨を沈着させます。この部分は、構造と柔軟性をもらたらす コラーゲン繊維が含まれます。マトリクスが合成されると 骨芽細胞は扁平になって骨の表面に存在するもの または骨細胞として骨に埋るものに区別されます。

Crockett, Julie C., Michael J. Rogers, Fraser P. Coxon, Lynne J. Hocking, and Miep H. Helfrich. "Bone Remodelling at a Glance." J Cell Sci 124, no. 7 (2011年4月1日): 991–98.[<a href="https://doi.org/10.1242/jcs.063032">出典</a>]

「Concise Review:Stem Cells in Osteoimmunology.」 幹細胞(オハイオ州デイトン) 35, no. 6 (2017年6月): 1461–67.[<a href="https://doi.org/10.1002/stem.2625" target="__blank">ソース</a>]

骨再形成

骨再形成（骨リモデリング）とは、破骨細胞による骨吸収と骨芽細胞による骨形成が連続的かつバランスよく行われることをいいます。成人の場合、骨量とカルシウムの恒常性の維持に役立ちます。機械的ストレスは、正常な維持と修復のプロセスの一部としてターンオーバー（代謝回転）を刺激しますが、いくつかのホルモンも骨再形成を制御します。 
 
 <h4>骨再形成を制御するホルモン</h4>
 
 副甲状腺ホルモン（PTH）は、骨吸収を制御することで血中カルシウム濃度の恒常性を維持しています。PTHは、血中カルシウム濃度の低下に応じて副甲状腺から分泌されます。PTHは、骨芽細胞を刺激して免疫分子を産生させ、前駆細胞から破骨細胞への分化を促進します。破骨細胞の活性化は骨吸収を促進し、鉱物化した骨基質が破壊されてカルシウムが血液中に放出されます。血中カルシウム濃度が回復すると、負のフィードバックループにより、PTHのさらなる放出が阻止されます。 
 
 <h4>骨粗鬆症（こつそしょうしょう）</h4>
 
 骨粗鬆症は、骨吸収が骨形成を上回り、骨密度が低下する病気です。骨粗鬆症は女性に多く見られ、特に閉経後に多く見られます。これは、女性ホルモンであるエストロゲンが骨再形成に重要な役割を果たしているためです。エストロゲンは、破骨細胞の形成を制限し、アポトーシスによる破骨細胞の破壊を促進します。これにより、骨形成量が骨吸収量を上回るようになります。しかし、更年期の女性では、エストロゲンの量が極端に減少します。そのため、骨吸収が骨形成を上回り、骨強度が低下し、骨折のリスクが高まります。

骨リモデリングは、破骨細胞による骨吸収と骨芽細胞による骨形成の連続的かつバランスの取れたプロセスです。大人では、それは維持するのに役立ちます...

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Biology

生物学

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ヒト生物学

Musculoskeletal System

筋骨格系

KEY TERMS AND CONCEPTS

主要用語と概念

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?

Human Skeleton: Bones, Cells, and Disease

The human skeleton is a living framework made of 206 bones in adults. Bones connect with cartilage, tendons, and ligaments. This system gives the body support, protects organs, and helps with movement and locomotion. The skeleton has two main parts: the axial skeleton and the appendicular skeleton. The axial skeleton has 80 bones and includes the skull, the vertebral column, and the rib cage. The cranium, or upper skull, has eight bones that enclose the brain, while the lower part of the skull...

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Inside a Long Bone

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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

Muscle Fibers, Tendons, and Contraction

Skeletal muscle moves the body by pulling on bones through tendons. Tendons are the connective tissue that attaches skeletal muscle to bones. When skeletal muscles contract, they create voluntary movement. Skeletal muscle is wrapped in layers of connective tissue. The outer layer is the epimysium, which helps protect the muscle. Beneath it, the perimysium surrounds and groups fasciculi, which are bundles of skeletal muscle cells called myocytes. These cells are also called skeletal muscle...

classification of skeletal muscle fibers

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muscle contraction

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cross-bridge cycle

Calcium Control in Muscle Contraction

Calcium control in muscle contraction depends on ATP, motor neurons, and the sliding action of actin and myosin. As a muscle contracts, the thin and thick filaments overlap more, and the sarcomere, which is the contractile unit of the muscle, becomes shorter. This process uses energy from ATP and happens in a repeating cycle at the molecular level. Myosin drives the movement of actin through a cross-bridge cycle. When ATP attached to the myosin head is hydrolyzed to ADP, myosin shifts into a...

motor units

How Motor Units Control Muscle Movement

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the spinal cord

Spinal Cord Structure and Dermatomes

The spinal cord is the main nerve pathway of the central nervous system. It carries sensory signals from the body to the brain and motor signals from the brain to the body. It begins at the foramen magnum, the opening at the base of the skull, and extends to the level of the first or second lumbar vertebra. In cross-section, the spinal cord is cylindrical and contains both gray matter and white matter. The central canal lies in the middle and is a remnant of the lumen of the primitive neural...

nociception

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Pain signaling begins when the body detects a harmful stimulus. Sharp objects, open flames, and corrosive chemicals can trigger this response. Sensory receptors called nociceptors, which sit on nerve endings, detect these noxious stimuli and use ion channels to turn them into electrical signals. Those electrical signals travel through sensory neurons to the brain, where they are experienced as pain. This warning system helps an organism avoid damage and stay safe. Pain is therefore an...

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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