Questions and Answers
What is the characteristic of collagen fibers in mature lamellar bone?
Parallel layers resulting in strong mature bone
What is the primary function of woven bone?
To facilitate rapid bone formation during fracture repair
What is the term for the functional unit of lamellar bone?
Osteon
What is the primary location of woven bone formation?
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What is the process by which woven bone is remodeled into lamellar bone?
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What is the characteristic of trabecular bone in bird bones?
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What is the role of osteoid in bone formation?
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What is the term for the channels that connect lacunae in osteons?
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What is the primary component of osteoid, making up approximately 90%?
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What is the role of parathyroid hormone (PTH) in bone metabolism?
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What is the function of osteoclasts in bone remodeling?
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Which of the following hormones inhibits bone resorption?
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What is the role of osteoblasts in bone remodeling?
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What is the composition of hydroxyapatite, the inorganic component of bone?
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Which of the following is involved in the mineralization of osteoid?
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What is the origin of stem cells that give rise to osteoclasts?
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What is the primary function of osteoblasts in bone tissue?
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What is the term for the thin channels running between lacunae in the Haversian system?
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What is the purpose of Howship's lacunae in bone remodeling?
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What is the origin of osteoclasts?
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What is the term for the canal that runs through the center of an osteon?
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What is the role of parathyroid hormone (PTH) in bone remodeling?
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What is the composition of cortical bone?
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What is the location of osteons in mature bone?
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What is the function of osteonectin and osteocalcin in bone development?
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What occurs if osteoid fails to mineralize?
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Which type of ossification occurs in flat bones of the skull and pelvis?
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What precedes endochondral ossification?
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What is the function of the physis?
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What is the term for the growth plate at the ends of bones?
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What is the term for the shaft of a long bone?
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What is the term for the region of bone tissue that regulates bone growth in width?
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What is the primary function of osteoblasts during bone formation?
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What is the type of bone that forms through the process of endochondral bone formation?
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What is the main difference between osteoid and bone tissue?
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What is the direction of blood flow in the cortex of young animals?
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What is the term for the process of bone tissue replacement and reshaping?
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What is the primary function of the metaphyseal arteries?
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What is the term for the mature, organized bone tissue that forms through the process of bone remodeling?
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What is the primary function of the bone marrow?
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Study Notes
Bone Structure
- Mature lamellar bone is hard and strong, with collagen fibers arranged in parallel layers, while woven bone is soft and weak, with disorganized collagen fibers
- Lamellar bone is formed slowly and is present in trabeculae and cortical bone, while woven bone is produced quickly and is present at sites of rapid bone formation (e.g. fracture repair, inflammation, neoplasia)
Osteon and Haversian System
- Osteon is the functional unit of lamellar bone, consisting of circles of bone around a central canal (Haversian canal) and interstitial bone between the circles
- Haversian canal is seen at the center of each osteon, with Volkmann's canals running in bone and connecting Haversian canals
Bone Cells
- Osteoblasts produce osteoid (the organic component of bone matrix) and initiate its mineralization, and can become osteocytes
- Osteocytes reside in lacunae surrounded by mineralized matrix, with long filopods to increase their cell area
- Osteoclasts are responsible for bone resorption, residing in shallow pits (Howship's lacunae) and releasing acid hydrolases for extracellular digestion
Regulation of Bone Metabolism
- Parathyroid hormone (PTH) stimulates bone resorption and promotes calcium absorption
- 1,25-dihydroxyvitamin D3 is required for normal bone growth and mineralization, and also stimulates bone resorption
- Calcitonin inhibits bone resorption
- Glucocorticoids inhibit bone formation and stimulate resorption
- Estrogen inhibits bone resorption
Bone Composition
- Osteoid (organic component) contains type I collagen, osteonectin, osteocalcin, proteoglycans, and growth factors
- Hydroxyapatite [Ca10(PO4)6(OH)2] is the inorganic component of bone
Bone Development
- Intramembranous ossification occurs in flat bones of the skull and pelvis, and on all periosteal surfaces throughout life, responsible for growth in width
- Endochondral ossification occurs in most bones, preceded by hyaline cartilage, responsible for growth in length
Bone Blood Supply
- Blood enters the marrow cavity of bones through nutrient, metaphyseal, and epiphyseal arteries
- In young animals, the cortex is supplied mainly from the endosteal surface and exits via periosteal veins
- With age, the cortex becomes increasingly dependent on periosteal arteries
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