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During bone development, which type of bone is produced first?
During bone development, which type of bone is produced first?
What is the primary function of osteoprogenitor cells in ossification centers?
What is the primary function of osteoprogenitor cells in ossification centers?
What is the outcome of continued matrix secretion and calcification in intramembranous ossification?
What is the outcome of continued matrix secretion and calcification in intramembranous ossification?
What is the origin of osteoblasts in intramembranous ossification?
What is the origin of osteoblasts in intramembranous ossification?
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What is the fate of mesenchymal regions that do not undergo ossification?
What is the fate of mesenchymal regions that do not undergo ossification?
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Which of the following bones is NOT formed through intramembranous ossification?
Which of the following bones is NOT formed through intramembranous ossification?
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What is the characteristic of bone formation in cranial flat bones?
What is the characteristic of bone formation in cranial flat bones?
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What is the result of the fusion of neighboring ossification centers?
What is the result of the fusion of neighboring ossification centers?
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What happens to the epiphyseal cartilage after completion of bone development?
What happens to the epiphyseal cartilage after completion of bone development?
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What is the primary function of chondrocytes in the zone of calcified cartilage?
What is the primary function of chondrocytes in the zone of calcified cartilage?
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What is the purpose of type X collagen in the zone of hypertrophy?
What is the purpose of type X collagen in the zone of hypertrophy?
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What occurs to the chondrocytes in the diaphysis side of the epiphyseal plate?
What occurs to the chondrocytes in the diaphysis side of the epiphyseal plate?
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How is the 'bone age' of a young person determined?
How is the 'bone age' of a young person determined?
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What is the function of the zone of reserve cartilage?
What is the function of the zone of reserve cartilage?
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What is the result of the opposing events of proliferation and destruction in the epiphyseal plate?
What is the result of the opposing events of proliferation and destruction in the epiphyseal plate?
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What is unique to the hypertrophic chondrocytes in developing bone?
What is unique to the hypertrophic chondrocytes in developing bone?
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What is the process by which osteoblasts develop from osteoprogenitor cells in the periosteum?
What is the process by which osteoblasts develop from osteoprogenitor cells in the periosteum?
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What happens to the epiphyses upon completion of bone development?
What happens to the epiphyses upon completion of bone development?
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What is the result of the activity of osteoclasts in the endosteum?
What is the result of the activity of osteoclasts in the endosteum?
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What type of bone is formed by osteoblasts settling in a layer over the spicules of calcified cartilage matrix?
What type of bone is formed by osteoblasts settling in a layer over the spicules of calcified cartilage matrix?
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What is the purpose of the proliferative zone in the epiphyseal growth plate?
What is the purpose of the proliferative zone in the epiphyseal growth plate?
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What is the significance of the epiphyseal plate's disappearance upon completion of bone development?
What is the significance of the epiphyseal plate's disappearance upon completion of bone development?
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What is the zone where bone tissue first appears?
What is the zone where bone tissue first appears?
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What is the process by which the circumference of long bones increases?
What is the process by which the circumference of long bones increases?
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What is the primary function of the bone collar in endochondral ossification?
What is the primary function of the bone collar in endochondral ossification?
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What is the result of hypertrophic chondrocytes releasing osteocalcin and alkaline phosphatase?
What is the result of hypertrophic chondrocytes releasing osteocalcin and alkaline phosphatase?
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What type of bone tissue is present in the central portion of compact bone?
What type of bone tissue is present in the central portion of compact bone?
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What is the purpose of the periosteum in endochondral ossification?
What is the purpose of the periosteum in endochondral ossification?
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What is the function of osteoblasts in the primary ossification center?
What is the function of osteoblasts in the primary ossification center?
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What is the significance of the fontanelles in newborn infants?
What is the significance of the fontanelles in newborn infants?
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What is the result of the expansion and remodeling of the primary and secondary ossification centers?
What is the result of the expansion and remodeling of the primary and secondary ossification centers?
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What is the name of the process by which most bones of the body are formed?
What is the name of the process by which most bones of the body are formed?
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Study Notes
Bone Development
- Bone development or osteogenesis occurs through two processes: intramembranous ossification and endochondral ossification.
Intramembranous Ossification
- Intramembranous ossification forms flat bones, such as those in the skull and jaws, scapula, and clavicle.
- It occurs within condensed sheets of embryonic mesenchymal tissue.
- Osteoprogenitor cells arise, proliferate, and form incomplete layers of osteoblasts around a network of developing capillaries.
- Osteoid secreted by osteoblasts calcifies, forming small irregular areas of woven bone with osteocytes in lacunae and canaliculi.
- Continued matrix secretion and calcification enlarge these areas, leading to the fusion of neighboring ossification centers.
- The anatomical bone forms gradually as woven bone matrix is replaced by compact bone that encloses a region of cancellous bone with marrow and larger blood vessels.
- Mesenchymal regions that do not undergo ossification give rise to the endosteum and periosteum of the new bone.
Endochondral Ossification
- Endochondral ossification forms most bones of the body, especially long bones.
- It takes place within a hyaline cartilage model of the bone to be formed.
- Ossification first occurs within a bone collar produced by osteoblasts that differentiate within the perichondrium (transitioning to periosteum) around the cartilage model diaphysis.
- The bone collar impedes diffusion of oxygen and nutrients into the underlying cartilage, causing local chondrocytes to swell up (hypertrophy), compress the surrounding matrix, and initiate its calcification.
- The hypertrophic chondrocytes eventually die, creating empty spaces within the calcified matrix.
- One or more blood vessels from the perichondrium (now the periosteum) penetrate the bone collar, bringing osteoprogenitor cells to the porous central region.
- Along with the vasculature, newly formed osteoblasts move into all available spaces and produce woven bone.
- The process in the diaphysis forms the primary ossification center, beginning in many embryonic bones as early as the first trimester.
Epiphyseal Growth Plate
- The epiphyseal cartilage is responsible for the growth in length of the bone and disappears upon completion of bone development at adulthood.
- Elimination of these epiphyseal plates (“epiphyseal closure”) occurs at various times with different bones and by about age 20 is complete in all bones.
- The epiphyseal growth plate shows distinct regions of cellular activity, including:
- The zone of reserve (or resting) cartilage
- The proliferative zone
- The zone of hypertrophy
- The zone of calcified cartilage
- The zone of ossification
Bone Growth
- Longitudinal growth of a bone occurs by cell proliferation in the epiphyseal plate cartilage.
- At the same time, chondrocytes in the diaphysis side of the plate undergo hypertrophy, their matrix becomes calcified, and the cells die.
- Osteoblasts lay down a layer of new bone on the calcified cartilage matrix.
- The epiphyseal plate does not change thickness, but is instead displaced away from the center of the diaphysis as the length of the bone increases.
- Growth in the circumference of long bones does not involve endochondral ossification but occurs through the activity of osteoblasts developing from osteoprogenitor cells in the periosteum by a process of appositional growth.
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Description
Learn about the two processes of bone development: intramembranous ossification and endochondral ossification, and how osteoblasts produce osteoid in each process.
