--- title: "Bone Resorption | General Biology I" description: "Bone resorption is the osteoclast-driven breakdown of bone that releases calcium and phosphate into blood, linking bone remodeling to mineral balance in General Biology I." canonical: "https://fiveable.me/college-bio/key-terms/bone-resorption" type: "key-term" subject: "General Biology I" unit: "Unit 38" --- # Bone Resorption | General Biology I ## Definition Bone resorption is the process where osteoclasts break down bone matrix and release calcium and phosphate into the bloodstream. In General Biology I, it shows how bone stays dynamic and helps regulate mineral levels. ## What It Is Bone resorption is the part of bone remodeling where osteoclasts dissolve old or damaged bone in General Biology I. Instead of bone being a static material, it is constantly being broken down and rebuilt. That turnover lets the skeleton adapt to stress, repair tiny injuries, and keep calcium and phosphate available for the body. Osteoclasts attach to the bone surface and create a small sealed space. Inside that space, they release acids and enzymes that dissolve the mineral and protein parts of bone. The mineral portion is mainly hydroxyapatite, which contains calcium and phosphate, so when bone is resorbed those ions can enter the bloodstream. This process is tightly matched with bone formation. Osteoblasts build new bone while osteoclasts remove old bone, so healthy skeletons stay balanced. If resorption speeds up too much, bone becomes less dense and more fracture-prone. If it slows down too much, old or damaged bone can stay in place longer than it should. Hormones help control the rate of resorption. Parathyroid hormone (PTH), for example, increases bone resorption when blood calcium is low. That makes bone a mineral reservoir, not just a support structure. The body can trade a little bone strength in the short term to protect calcium-dependent processes like nerve signaling, muscle contraction, and blood clotting. A good way to picture it is as a remodeling site. One team clears away old material, and another team replaces it. Bone resorption is the clearing step, and without it, bone cannot properly renew itself or respond to changing mechanical load. ## Why It Matters Bone resorption shows up anywhere General Biology I connects structure to function. It explains why bone is living tissue, not just a rigid frame, and it ties skeletal biology to homeostasis. When you see calcium regulation, hormone signaling, or skeletal remodeling in a chapter, resorption is often the process that makes the change happen. It also helps you make sense of disease. If resorption outpaces formation for a long time, bones lose density and osteoporosis becomes more likely. If the balance shifts the other way, bones can become abnormally dense but still unhealthy. So this term is a shortcut to one big idea in biology: body systems stay stable by continually adjusting their structures. In lab or exam-style questions, bone resorption helps you read cause and effect. A rise in PTH, a drop in blood calcium, or an increase in osteoclast activity all point toward more resorption. That chain is common in questions about feedback loops, mineral storage, and bone turnover. ## Connections ### Osteoclasts Osteoclasts are the cells that carry out bone resorption. If a question asks which cell breaks down bone, this is the term to recognize. They dissolve the mineralized matrix so calcium and phosphate can be released, which makes them central to remodeling and calcium balance. ### Osteoblasts Osteoblasts do the opposite job from osteoclasts, they build new bone. Bone resorption and bone formation happen together in remodeling, so these two cell types are usually paired in questions about bone turnover. A healthy skeleton depends on both being balanced over time. ### [Calcium homeostasis](/college-bio/key-terms/calcium-homeostasis) Bone resorption is one of the body’s ways to keep blood calcium in range. When calcium drops, resorption can increase and release calcium from bone into the bloodstream. That makes this term a direct link between the skeleton and the endocrine system. ### [Bone remodeling](/college-bio/key-terms/bone-remodeling) Bone resorption is one step in bone remodeling, the ongoing cycle of breaking down and rebuilding bone. Remodeling helps bones repair microdamage and adjust to mechanical stress. If you see a question about turnover or adaptation, resorption is usually part of the answer. ## On the AP Exam A quiz question might ask you to identify which cells increase when blood calcium is low, or to trace how PTH affects bone. In a diagram, you may need to label osteoclast activity as the resorption side of remodeling. If the prompt gives a scenario like weak, porous bones, you should connect it to excessive resorption or an imbalance between osteoclasts and osteoblasts. In short-answer or discussion questions, use the term to explain how the skeleton contributes to mineral homeostasis, not just support. ## Bone resorption vs Bone remodeling Bone resorption is only the breakdown side of the process, while bone remodeling includes both resorption and new bone formation. If a question asks for the whole cycle of bone renewal, use remodeling. If it asks specifically about bone being broken down and minerals being released, use resorption. ## Key Takeaways - Bone resorption is the breakdown of bone tissue by osteoclasts, which releases calcium and phosphate into the blood. - It is one half of bone remodeling, the other half being bone formation by osteoblasts. - The process helps bones adapt to stress and repair small areas of damage over time. - Hormones like parathyroid hormone can increase resorption when blood calcium is low. - Too much resorption compared with formation can weaken bones and contribute to osteoporosis. ## FAQs ### What is bone resorption in General Biology I? Bone resorption is the process where osteoclasts break down bone matrix and release minerals into the bloodstream. In General Biology I, it comes up as part of bone remodeling and calcium homeostasis. It shows that bone is living tissue that is constantly being renewed. ### What cells carry out bone resorption? Osteoclasts carry out bone resorption. They attach to the bone surface, dissolve the mineral matrix, and release calcium and phosphate. If you see a question contrasting bone builders and bone breakers, osteoclasts are the bone-breaking cells. ### How is bone resorption different from bone remodeling? Bone resorption is the breakdown phase, while bone remodeling is the full cycle of resorption followed by new bone formation. Remodeling describes the whole maintenance process, but resorption refers only to the removal of old bone. That distinction matters in cell and hormone questions. ### Why does parathyroid hormone increase bone resorption? Parathyroid hormone increases bone resorption when blood calcium is low. Breaking down bone releases calcium into the bloodstream, which helps restore normal levels. This is a classic example of bone acting as a mineral store for homeostasis. ## Related Study Guides - [38.2 Bone](/college-bio/unit-38/2-bone/study-guide/TehCFt0dwHujxNN6) ## About This Document Canonical Fiveable pages are available as Markdown at the same path plus `.md`. - [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns - [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing - [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`) - [MCP server for AP teachers](https://fiveable.me/mcp/teachers): a teacher's classes, assignments and AP-rubric grading (`https://fiveable.me/api/mcp/teacher`) ## Structured Data ```json {"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/college-bio/key-terms/bone-resorption#resource","name":"Bone Resorption | General Biology I","url":"https://fiveable.me/college-bio/key-terms/bone-resorption","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/college-bio/key-terms/bone-resorption#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:21:07.934Z","isPartOf":{"@type":"Collection","name":"General Biology I Key Terms","url":"https://fiveable.me/college-bio/key-terms"},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/college-bio/key-terms/bone-resorption#term","name":"Bone resorption","description":"Bone resorption is the process where osteoclasts break down bone matrix and release calcium and phosphate into the bloodstream. 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