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Questions and Answers
What is the role of osteoprogenitor cells in bone tissue?
What is the role of osteoprogenitor cells in bone tissue?
Which type of cell is responsible for the actual deposition of bone matrix?
Which type of cell is responsible for the actual deposition of bone matrix?
Where are osteocytes located within the bone structure?
Where are osteocytes located within the bone structure?
What is the primary function of osteoid secreted by osteoblasts?
What is the primary function of osteoid secreted by osteoblasts?
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Which components are found in the matrix of bone tissue?
Which components are found in the matrix of bone tissue?
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How do osteocytes communicate with each other?
How do osteocytes communicate with each other?
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What is the main source of osteoblasts in bone tissue?
What is the main source of osteoblasts in bone tissue?
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What general function do specialized bone cells serve?
What general function do specialized bone cells serve?
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What is the primary function of osteoclasts in the formation of the medullary cavity?
What is the primary function of osteoclasts in the formation of the medullary cavity?
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Which zone of the epiphyseal plate is closest to the diaphysis?
Which zone of the epiphyseal plate is closest to the diaphysis?
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What effect do sex hormones have during puberty on bone growth?
What effect do sex hormones have during puberty on bone growth?
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What initiates growth in thickness (appositional growth) of bone?
What initiates growth in thickness (appositional growth) of bone?
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What happens to the epiphyseal plate as osteoblasts increase their activity?
What happens to the epiphyseal plate as osteoblasts increase their activity?
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How does bone remodeling contribute to bone health?
How does bone remodeling contribute to bone health?
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What is a consequence of regular weight training on bone structure?
What is a consequence of regular weight training on bone structure?
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Which of the following best describes the role of the endosteum in bone structure?
Which of the following best describes the role of the endosteum in bone structure?
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What is the primary function of osteoclasts in bone tissue?
What is the primary function of osteoclasts in bone tissue?
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Which of the following best describes the structure of osteoclasts?
Which of the following best describes the structure of osteoclasts?
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What is the purpose of the sealing zone in osteoclast function?
What is the purpose of the sealing zone in osteoclast function?
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Which organic material makes up about one-third of the bone matrix?
Which organic material makes up about one-third of the bone matrix?
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What primarily forms the inorganic component of the bone matrix?
What primarily forms the inorganic component of the bone matrix?
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Which protein binds calcium ions to collagen in the bone matrix?
Which protein binds calcium ions to collagen in the bone matrix?
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What is the primary function of calcitonin in blood calcium regulation?
What is the primary function of calcitonin in blood calcium regulation?
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What role does the periosteum play in bone structure?
What role does the periosteum play in bone structure?
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What does the ruffled border of osteoclasts release to aid in bone resorption?
What does the ruffled border of osteoclasts release to aid in bone resorption?
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Which hormone directly stimulates the resorption of calcium from bone?
Which hormone directly stimulates the resorption of calcium from bone?
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What is the first stage in the typical repair of bone fractures?
What is the first stage in the typical repair of bone fractures?
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What happens during the reparative phase of bone repair?
What happens during the reparative phase of bone repair?
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During which phase do osteoblasts replace spongy bone with compact bone?
During which phase do osteoblasts replace spongy bone with compact bone?
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Which condition describes a bone that heals in an abnormal position?
Which condition describes a bone that heals in an abnormal position?
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What is a major consequence of nonunion in bone healing?
What is a major consequence of nonunion in bone healing?
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What does calcitriol do in terms of calcium levels in the body?
What does calcitriol do in terms of calcium levels in the body?
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What type of cells do osteoclasts originate from?
What type of cells do osteoclasts originate from?
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Which lamella surrounds an osteon?
Which lamella surrounds an osteon?
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During which phase of bone repair is a fracture hematoma formed?
During which phase of bone repair is a fracture hematoma formed?
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What material is primarily found in spongy bone?
What material is primarily found in spongy bone?
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What is the primary function of osteoblasts?
What is the primary function of osteoblasts?
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What type of growth occurs at the epiphyseal plate?
What type of growth occurs at the epiphyseal plate?
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What is the role of chondroblasts during bone repair?
What is the role of chondroblasts during bone repair?
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Which hormone is known to help maintain blood calcium levels?
Which hormone is known to help maintain blood calcium levels?
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Study Notes
Bone Histology
- Bone tissue is composed of specialized cells, bone matrix, and a specific organization.
- Cells are classified as:
- Osteoprogenitor cells: Unspecialized stem cells that give rise to osteoblasts, located in the periosteum and endosteum, derived from mesenchymal tissue.
- Osteoblasts: Immature bone cells that build bone in a process called bone deposition, found on the surface of bones, typically appearing as cuboidal-shaped cells in groups, osteoblasts secrete osteoid.
- Osteocytes: Mature osteoblasts surrounded by bone matrix, located within lacunae, essential for detecting mechanical stress and maintaining bone matrix, appear as small cells surrounded by compact bone, communicate with other osteocytes via canaliculi.
- Osteoclasts: Large, multi-nucleated bone cells that carve away bone in a process known as bone resorption, derived from monocytes (a type of leukocyte), found on the surface of bones, appear as massive, multinucleated cells with resorption lacunae, sealing zone, and ruffled border.
- Bone matrix is composed of organic and inorganic materials.
- Organic materials: (about 1/3 of bone) provide flexibility and a framework for the inorganic mineral salts, mainly secreted by osteoblasts as osteoid, collagen (I) is the most abundant organic substance in bone.
- Inorganic materials: (about 2/3 of bone) give bones their strength and rigidity, make up calcium hydroxyapatite which is the most abundant inorganic substance.
- Periosteum: Dense irregular connective tissue covering bone, comprises an outer fibrous layer (collagen (I), blood vessels, and nerves) and an inner cellular layer (osteoprogenitor cells)
- Endosteum: Connective tissue lining the medullary (marrow) cavity and the canals that pass through compact bone, composed of osteoprogenitor cells.
Bone Tissue Types
- Compact bone: Dense, solid bone that makes up the outer layer of most bones, it is resistant to compression and bending stress.
- Spongy (cancellous) bone: Lighter, porous bone that contains a network of trabeculae which forms the inner layer of most bones, it also helps to reduce weight, allow for bone marrow production, and provides strength.
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Lamellae: Concentric rings of bone matrix that make up osteons.
- Concentric lamellae: Rings in osteons surrounding the central canal.
- Interstitial lamellae: Incomplete lamellae between osteons.
- Circumferential lamellae: Rings located at the periphery of compact bone.
- Osteons: Cylindrical structures in compact bone that contain a central canal, lamellae, lacunae, and canaliculi.
Bone Formation
- Intramembranous ossification: Formation of bone directly from mesenchymal tissue, forming flat bones like the skull, clavicle, and jaw.
- Endochondral ossification: Begins with a hyaline cartilage model that is replaced by bone, forming most of the long bones in the body.
Bone Growth
- Lengthwise growth: Occurs at the epiphyseal plate, a region of hyaline cartilage between the epiphysis and diaphysis of a long bone, divided into five zones.
- Growth in thickness (appositional): Occurs by adding new bone tissue to the outer surface of existing bone, controlled by periosteal osteoprogenitor cells, creates new osteons.
Bone Remodeling
- Continuous process of bone replacement, adaptation of bone structure to different stresses.
- Osteoclasts resorb old bone tissue, Osteoblasts deposit new bone tissue.
Calcium Homeostasis
- Regulation of blood calcium levels through the action of hormones:
- Calcitonin (CT): Decreases blood calcium by inhibiting osteoclastic bone resorption and accelerating calcium deposition into bones.
- Parathyroid hormone (PTH): Increases blood calcium by indirectly stimulating osteoclastic bone resorption and stimulating the formation of calcitriol.
- Calcitriol: Increases blood calcium levels by promoting calcium absorption in the gastrointestinal tract.
Bone Repair
- Reactive (inflammatory) phase: Early inflammatory stage involving blood clot formation and cell death, debris is removed by macrophages and osteoclasts.
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Reparative phase: Formation of a fibrous cartilage callus following the reactive phase.
- Fibrocartilage callus: Connects the broken bone, formed by fibroblasts and chondroblasts.
- Bony callus: Replaces the fibrocartilage callus with spongy bone trabeculae formed by osteoblasts.
- Bone remodeling phase: Reshaping of the bony callus by osteoclasts, replacement of spongy bone with compact bone.
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Complications:
- Malunion: Bone heals in an abnormal position.
- Nonunion: Bone fails to heal, possibly due to inadequate blood supply, interference from other tissues, or excessive mobility.
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Description
Test your knowledge of bone histology with this quiz that explores the specialized cells involved in bone tissue. Understand the roles of osteoprogenitor cells, osteoblasts, osteocytes, and osteoclasts, as well as their functions and locations within the bone matrix. Challenge yourself on the key concepts of bone composition and organization.
