Ossification = Osteogenesis Ossification = Osteogenesis

• Parts of the fetal skeleton form during the first few weeks after conception • By the end of the 8th week, the skeletal pattern is formed : cartilage & connective tissue membranes

There are two classifications of ossification: Intramembranous: Endochondral: *Replacement of *Replacement of sheetlike connective hyaline cartilage tissue with bony tissue with bony tissue *Primarily in flat bones *Most bones are of skull & some irregular formed this way bones Intramembranous Ossification

• Osteoblasts migrate to the membrane and deposit bony matrix around themselves. Intramembranous Ossification

• Osteoblasts migrate to the membrane and deposit bony matrix around themselves. • Once surrounded by matrix, they are called osteocytes. Intramembranous Ossification

• Osteoblasts migrate to the membrane and deposit bony matrix around themselves. • Once surrounded by matrix, they are called osteocytes. • “Islands” of bone grow outward from the origin and connect with one anaother Intramembranous Ossification

• Osteoblasts migrate to the membrane and deposit bony matrix around themselves. • Once surrounded by matrix, they are called osteocytes. • “Islands” of bone grow outward from the origin • After formation, growth and connect with one continues only from border anaother cells Endochondral Ossification

• Hyaline cartilage ‘bones’ are infiltrated with blood vessels & osteoblasts. • Formation of ‘Collar’ of compact bone around diaphysis Endochondral Ossification

• At the same time, cartilage in center of diaphysis begins to disintegrate • Replaced with spongy bone * Primary Ossification Center* Ossification continues from the primary ossification center towards the ends of the bones. Ossification continues from the primary ossification center towards the ends of the bones. After spongy bone is formed in diaphysis, osteoclasts break it down to open up medullary cavity Ossification continues from the primary ossification center towards the ends of the bones. After spongy bone is formed in diaphysis, osteoclasts break it down to open up medullary cavity The cartilage in the epiphysis continues to grow, so developing bone increases in length Ossification continues from the primary ossification center towards the ends of the bones. After spongy bone is formed in diaphysis, osteoclasts break it down to open up medullary cavity The cartilage in the epiphysis continues to grow, so developing bone increases in length After birth, secondary ossification centers form in epiphyses – ossification is similar, except spongy bone is not broken down. Ossification continues from the primary ossification center towards the ends of the bones. After spongy bone is formed in diaphysis, osteoclasts break it down to open up medullary cavity The cartilage in the epiphysis continues to grow, so developing bone increases in length After birth, secondary ossification centers form in epiphyses – ossification is similar, except spongy bone is not broken down. Once ossification is complete – the cartilage is all replaced except at the surface of the epiphysis [articular cartilage] and between the diaphysis and epiphysis [epiphyseal plate]