Bone B

Front

Ossification (osteogenesis)

Back

 is the process of bone tissue formation

◦Formation of bony skeleton begins in month 2 of development

◦Replaces connective tissue

◦Postnatal bone growth occurs until early adulthood

◦Bone remodeling and repair are lifelong

Front

Endochondral ossification

Back

◦Bone forms by replacing hyaline cartilage

◦Bones are called cartilage (endochondral) bones

◦Form most of skeleton

Front

Intramembranous ossification

Back

◦Bone develops from fibrous membrane (dense irregular fibrous c.t.)

◦Bones are called membrane bones

Front

Endochondral ossification

Back

◦Forms essentially all bones inferior to base of skull, except clavicles

◦Begins late in month 2 of development

◦Uses previously formed hyaline cartilage models

◦Requires breakdown of hyaline cartilage prior to ossification

◦Begins at primary ossification center in center of shaft

◦Blood vessels infiltrate perichondrium, converting it to periosteum

◦Mesenchymal cells specialize into osteoblasts

Front

What are the five main steps in the process of endochondral ossification

Back

1.Bone collar forms around diaphysis of cartilage model

2.Central cartilage in diaphysis calcifies, then develops cavities

3.Periosteal bud invades cavities, leading to formation of spongy bone

◦Bud is made up of blood vessels, nerves, red marrow, osteogenic cells, and osteoclasts

4.Diaphysis elongates, and medullary cavity forms

◦Secondary ossification centers appear in epiphyses

5.Epiphyses ossify

◦Hyaline cartilage remains only in epiphyseal plates and articular cartilages

Front

Intramembranous ossification

Back

◦Begins within fibrous (dense irregular) connective tissue membranes formed by mesenchymal cells (multipotent stem cells for bone, cartilage, and marrow adipose)

◦Forms frontal, parietal, occipital, temporal, and clavicle bones

Front

Four major steps are involved in intramembranous ossification

Back

1.Ossification centers are formed when mesenchymal cells cluster and become osteoblasts

2.Osteoid is secreted from the osteoblasts, and then calcifies

3.Woven bone is formed when osteoid is laid down around the developing blood vessels, resulting in trabeculae

◦Outer layer of woven bone forms periosteum

4.Lamellar bone replaces woven bone near the outer edge/periosteum, and red marrow appears within

Front

Postnatal bone growth

Back

 Long bones grow lengthwise by interstitial (longitudinal) growth of epiphyseal plate

 Bones increase thickness through appositional growth

 Bones stop growing during adolescence

◦Some facial bones continue to grow slowly through life

Front

Interstital growth

Back

 Interstitial growth requires presence of epiphyseal cartilage in the epiphyseal plate

 Epiphyseal plate maintains constant thickness

◦Rate of cartilage growth on one side balanced by bone replacement on other

Front

Epiphyseal plate consists of five zones

Back

1.Resting (quiescent, reserve) zone

2. Proliferation (growth) zone

3. Hypertrophic (maturation) zone

4. Calcification zone

5. Ossification (osteogenic) zone