Name: how hormones control bone turnover
Uploaded: 2025-10-23T11:49:19.000Z
Duration: 1 min 40 s
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From Molecules to Organisms: Structures and Processes

HS-LS1-2

Bone Remodeling

אפילו בתוך שלד בוגר, עצמות הן רקמות פעילות הממשיכות לעבור שינויים באריכטקטורה. תהליך זה, הנקרא שחלוף עצם, מורכב משלבים שווים של פירוק העצם, הסרתה, והנחת רקמה חדשה. כאשר תאי עצם בוגרים, אוסטאוציטים, חשים לחץ מכני, הם משדרים תאים לאתר העצם.לדוגמה, הקצוות של עצם הירך, אשר מוחלפים כל שישה חודשים. במהלך הפירוק, סוג תא אחד, אוסטאוקלסטים, נאחזים בחוזקה בפני השטח. על-ידי הפרשת אנזימים ליזוזומליים ופרוטוני מימן, הם יכולים לפרק את המרכיבים האורגניים, תוך יצירת חללי ארוזיה על-ידי עיכול של המטריצה הישנה או הפגומה.סידן גם משוחרר לתוך הדם וממלא תפקיד בלולאת המשוב ההורמונלית. ברגע שהחומר מפורק, אוסטאוקלסטים משמידים את עצמם באפופטוזה, מה שמונע את המשך פירוק העצם. לתחילת השיקום, תאים חד-גרעיניים מופיעים על פני השטח בהכנה לשלב הבא.בשלב ההיווצרות, האוסטאובלסטים נכנסים אל החלל ומניחים עצם חדשה על-ידי ההתגרמות של המטריצה האורגנית המכונה אוסטאואיד. חלק זה כולל סיבי קולגן שתורמים למבנה ולגמישות. לאחר סינתזת מטריצה, אוסטאובלסטים יכולים להפוך לתאים שטוחים המרפדים את העצם, או לתאים הקבורים בעצם כאוסטאוציטים.

Crockett, Julie C., Michael J. Rogers, Fraser P. Coxon, Lynne J. Hocking ו-Miep H. Helfrich. "שיפוץ עצם במבט חטוף." J Cell Sci 124, no. 7 (אפריל 1, 2011): 991-98. [<a href="https://doi.org/10.1242/jcs.063032">מקור</a>]

פיירו, פ 'א', ג 'יי א' נולטה, ו I. E. Adamopoulos. "סקירה תמציתית: תאי גזע באוסטאימונולוגיה." תאי גזע (דייטון, אוהיו) 35, מס '6 (יוני 2017): 1461–67. [<a href="https://doi.org/10.1002/stem.2625" target="__blank">מקור</a>]

חידוש עצמות

<div style="direction:rtl">חידוש עצם הוא תהליך מתמשך ומאוזן של ספיגת עצם על ידי אוסטאוקלסטים ויצירת עצם על ידי אוסטאובלסטים. אצל מבוגרים, תהליך זה עוזר לשמור על מסת העצם והומאוסטזיס של סידן. בעוד שלחץ מכני יכול לעורר תחלופה כחלק מתהליך התחזוקה והשיקום הרגיל, מספר הורמונים מווסתים גם בנייה מחדש של עצם. <h4>בקרה הורמונלית של בניית עצם</h4> הורמון הפרתירואיד (PTH) שומר על שליטה הומאוסטטית על רמות הסידן בדם על ידי ויסות ספיגת העצם. PTH משתחרר מבלוטות הפאראתירואיד בתגובה לרמות נמוכות של סידן בדם. הוא מגרה אוסטאובלסטים לייצר מולקולות חיסוניות המקדמות את ההתמיינות של תאי קודמים לאוסטאוקלסטים. הפעלת אוסטאוקלסטים מעודדת ספיגת עצם, וגורמת למטריצת העצם המינרלית להתפרק ולשחרר סידן לדם. כאשר רמות הסידן בדם משוחזרות, לולאת משוב שלילי מונעת שחרור נוסף של PTH. <h4>אוסטאופורוזיס</h4> אוסטאופורוזיס היא מחלה שבה ספיגת העצם עולה על היווצרות העצם, וכתוצאה מכך צפיפות העצם מופחתת. אוסטאופורוזיס נפוץ יותר בנשים, במיוחד לאחר גיל המעבר. זאת בשל התפקיד הקריטי שממלא הורמון המין הנשי אסטרוגן בשיפוץ העצם. אסטרוגן מגביל את היווצרות אוסטאוקלסטים ומקדם את הרס שלהם באמצעות אפופטוזיס. זה מבטיח שיצירת עצם גבוהה יותר מספיגת עצם. עם זאת, רמות האסטרוגן יורדות בצורה חמורה אצל נשים בגיל המעבר. לכן, ספיגת העצם עולה על יצירתה, מה שמוביל לאובדן חוזק העצם ולסיכון מוגבר לשברים.</div>

עיצוב מחדש של עצם הוא תהליך מתמשך ומאוזן של ספיגת עצם על ידי אוסטאוקלסטים ויצירת עצם על ידי אוסטאובלסטים. אצל מבוגרים, זה עוזר לשמור על ...

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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

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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

Skeletal Muscle Fiber Speed and Energy

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muscle contraction

Nerve Signals That Trigger 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...

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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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HS-LS1-3

How Hormones Control Bone Turnover

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