What are the 2 types of ossification?
- Intramembranous
2. Endochondral
What is ossification?
Formation of bones by the replacement of pre-existing CT
What bones are formed from intramembranous ossification?
Flat bones e.g. cranial bones
How many stages are there in intramembranous ossification?
4
What occurs at stage 1 of intramembranous ossification?
- Mesenchymal cells differential into osteoblasts
- Cluster of osteoblasts form ossification centre
What is the function of an ossification centre?
Lay down osteoid
What occurs at stage 2 of intramembranous ossification?
- Mineralisation of osteoid to produce island of bone
- Trapped osteoblasts become osteocytes
What occurs at stage 3 of intramembranous ossification?
- Islands of bone join to form trabeculae
- Mesenchyme cells at edges condense to form periosteum
What occurs at stage 4 of intramembranous ossification?
- Red marrow develops from mesenchymal cells in trabecular spaces
What bones are formed from endochondral ossification?
Long bones of the body
How many stages are involved in endochondral ossification?
5
Why is endochondral ossification called so?
Involves the ossification of a hyaline cartilage template
What makes up the hyaline cartilage template involved in endochondral ossification?
Hyaline deposited in the shape of the bone within a mass of mesenchymal tissue
What occurs at stage 1 of endochondral ossification?
- Cartilage cells in central diaphysis die to leave cavities
- Perichondrium produces osteoblasts which lay down bone collar by IM ossification
What occurs at stage 2 of endochondral ossification?
- Cartilage matrix in centre continues to deteriorate
- Diaphysis diameter increases by bone deposition on outside and resorption on inside
- Chondrocytes in bone multiply, increasing length and breadth
What occurs at stage 3 of endochondral ossification?
- Capillaries penetrate diaphysis carrying in osteoprogenitor cells
- Osteoprogenitor cells become osteoblasts and set up primary ossification centre
- Bone laid down to replace lost cartilage in centre
What occurs at stage 4 of endochondral ossification?
- Capillaries penetrate epiphyses of bone
- Osteoprogenitor cells pulled into epiphyses and produce secondary ossification centres
- Formation of medullary cavity
When does stage 4 of endochondral ossification occur?
Approx. at birth
What occurs at stage 5 of endochondral ossification?
- Ossification of epiphysis is complete
- Cartilage only remains in epiphyseal growth plate and articular cartilage
What are the 5 zones of the epiphyseal growth plate?
- Resting
- Proliferate
- Hypertrophic
- Ossifying Cartilage
- Bone Deposition
What occurs in the hypertrophic zone?
Osteoblasts get bigger and begin to calcify
What is the weakest part of the skeleton?
Joints
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Skin39
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Cartilage and Bone40
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Ossification22
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Ordinary Connective Tissue51
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Epithelium50
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Muscles28
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Nerve56
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Taste32
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Saliva30
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Oral Mucosa40
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Tooth Morphology 141
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Dentin29
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Enamel35
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Periodontal Ligament and Eruption21
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Pulp36
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Deciduous Teeth24
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Early Tooth Development34
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Shedding and Replacement30
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Root Development35
