Name: how hormones control bone turnover
Uploaded: 2025-10-23T11:49:19.000Z
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Bone Remodeling

Даже в скелете взрослого человека, кости являются активными тканями, претерпевающими постоянные изменения в архитектуре. Этот процесс называется ремоделированием костей и состоит из равных фаз:костной резорбции, её удаления и размещения новой ткани. Когда зрелые костные клетки, остеоциты, ощущают механическое напряжение, они сигналят клеткам на участке кости, например, на концах бедренной кости, которые заменяются каждые шесть месяцев.Во время резорбции один тип клеток, остеокласты, накрепко прилипают к поверхности. Секретируя лизосомальный фермент и протоны водорода, они могут повредить органические компоненты, создавая эрозионные полости по мере того, как они переваривают старую или повреждённую матрицу. Кальций также выпускается в кровь и играет свою роль в гормональной петле обратной связи.После растворения материала происходит саморазрушение остеокласта через апоптоз, что препятствует дальнейшему разрушению кости. Чтобы начать обратный ход, на поверхности появляются мононуклеарные клетки для подготовки к следующему шагу. На этапе формирования, остеобласты перемещаются в полость и создают новые костные отложения через окостенение органической матрицы, известной как остеоид.Эта часть включает в себя коллагеновые волокна, которые способствуют структуре и гибкости. После синтеза матрицы, остеобласты могут дифференцироваться в сплюснутые клетки выстилки кости, или закапываются в кость как остеоциты.

Крокетт, Джули К., Майкл Дж. Роджерс, Фрейзер. Коксон, Линн Дж. Хокинг и Мип Х. Хелфрич. "Краткий обзор костной ткани." J Cell Sci 124, No7 (1 апреля 2011 г.): 991–98. [<a href="https://doi.org/10.1242/jcs.063032">исходник</a>]

Фиерро, Ф. А., Д. А. Нолта и И. Э. Адамопулос. «Краткий обзор: стволовые клетки в остеоиммунологии». Стволовые клетки (Дейтон, Огайо) 35, No 6 (июнь 2017 г.): 1461–67. [<a href="https://doi.org/10.1002/stem.2625" target="__blank">Источник</a>]

Ремоделирование костной ткани

Ремоделирование кости - это непрерывный и сбалансированный процесс резорбции кости остеокластами и образования кости остеобластами. У взрослых он помогает поддерживать костную массу и гомеостаз кальция. В то время как механический стресс может стимулировать обновление как часть нормального процесса поддержания и восстановления, некоторые гормоны также регулируют ремоделирование костей. 

<h4> Гормональный контроль ремоделирования костей </h4>

 Гормон паращитовидной железы (ПТГ) поддерживает гомеостатический контроль уровня кальция в крови, регулируя резорбцию костей. ПТГ высвобождается из паращитовидных желез в ответ на низкий уровень кальция в крови. Он стимулирует остеобласты к выработке иммунных молекул, которые способствуют дифференцировке клеток-предшественников в остеокласты. Активация остеокластов способствует резорбции кости, в результате чего минерализованный костный матрикс разрушается и высвобождает кальций в кровь. Когда уровень кальция в крови восстанавливается, петля отрицательной обратной связи предотвращает дальнейшее высвобождение ПТГ. 

<h4> Остеопороз </h4>

 Остеопороз - это заболевание, при котором резорбция кости превышает образование кости, что приводит к снижению плотности кости. Остеопороз чаще встречается у женщин, особенно после менопаузы. Это связано с критической ролью женского полового гормона - эстрогена - в ремоделировании костей. Эстроген ограничивает образование остеокластов и способствует их разрушению посредством апоптоза. Это гарантирует, что образование кости выше резорбции кости. Однако у женщин в период менопаузы уровень эстрогена сильно снижается. Следовательно, резорбция кости опережает ее создание, что приводит к потере прочности кости и повышенному риску переломов.

Ремоделирование кости – это непрерывный и сбалансированный процесс резорбции кости остеокластами и формирования костной ткани остеобластами. У взрослых он помогает поддерживать ...

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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?

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...

bone structure

Inside a Long Bone

Inside a long bone, osseous tissue is organized into two main types: cortical bone and cancellous bone. A femur is a clear example of this structure. The bone also includes outer coverings and inner spaces that support growth, repair, and blood cell production. Cortical bone, also called compact bone, forms the dense outer layer along the diaphysis, or shaft. It is covered by the periosteum, a membrane with connective tissue, capillaries, and nerves. Beneath the cortical layer is the medullary...

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Types of Joints in the Human Body

Joints are the places where adjacent bones connect. They are also called articulations or articular surfaces. Joints help the body move and stay stable. Joints can be classified by structure or by function. Structural classification depends on the material that forms the joint and whether there is a space between the bones. By structure, joints are fibrous, cartilaginous, or synovial. Fibrous joints are connected by fibrous tissue and have no cavity between the bones. Because of this, they do...

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

Skeletal Muscle Fiber Speed and Energy

Skeletal muscle fibers can be grouped by how fast they contract and how they make ATP, the energy cells use for movement. These differences also shape their physical features. Most human muscles contain all three fiber types, but in different amounts. Slow oxidative fibers, also called slow-twitch fibers, appear red because they have many capillaries and high levels of myoglobin, an oxygen-storing protein. They also contain more mitochondria, which make ATP through oxidative phosphorylation,...

muscle contraction

Nerve Signals That Trigger Muscle Contraction

Nerve signals trigger muscle contraction in both skeletal and smooth muscle, but the two muscle types use different control systems. In skeletal muscle, the signal begins at the motor end plate, which is the synapse between a motor neuron and a muscle fiber. In smooth muscle, contraction is controlled by the autonomic nervous system and happens without conscious control. In skeletal muscle, motor nerve terminals release acetylcholine. This neurotransmitter binds to receptors on the sarcolemma,...

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

Motor units control skeletal muscle movement. A motor unit includes one efferent motor neuron, which carries signals away from the central nervous system, and all of the muscle fibers it innervates. A single motor neuron can connect with multiple muscle fibers, but each muscle fiber is innervated by only one motor neuron. Lower motor neurons are the efferent neurons that control skeletal muscle, the most abundant type of muscle in the body. Their cell bodies are found in the spinal cord or...

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...

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Pain Signaling and Inflammation

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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Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis. [Clarification Statement: Examples of investigations could include heart rate response to exercise, stomate response to moisture and temperature, and root development in response to water levels.] [Assessment Boundary: Assessment does not include the cellular processes involved in the feedback mechanism.]

HS-LS1-3

How Hormones Control Bone Turnover

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