Bone Formation And Remodeling

Front 1

What is bone formation?

Back 1

Ossification (ossi-bone, fication-making)

Front 2

Initial bone formation in an embryo:

Back 2

Two methods:

METHOD 1-

Only occurs in the flat bone of the skull and the mandible during the first 6 weeks of development.

Occurs in between the two membranes that are formed from MESENCHYME (embryonic connective tissue from which all other connective tissues arise).

METHOD 2:

Endochondral Ossification:

Bone formation within hyaline cartilage that develops from Mesenchyme.

Both methods involve the replacement of connective tissue with bone, they're simply different methods.

Front 3

What are mesenchymal cells?

Back 3

Stem cells that can differentiate into a variety of cells types;

Osteoblasts - bone cells

Chondrocytes - cartilage cells

Myocytes - muscle cells

Adipocytes - fat cells

Front 4

Process of intramembranous ossification

Back 4

1) Development of ossification centre:

DICT 'CENTRE where bone forms'

Mesenchymal cells differentiate to osteogenic (stem) cells then develop into osteoblasts.

2) calcification:

Osteoblasts sprout cells that secrete ECM and surround themselves. They are then called Osteocytes (mature) that lie in lacuna and extend into canuliculi.

Within days other minerals are deposited in the ECM causing calcification.

3) Formation of Trabeculae:

As the ECM forms, it forms trabeculae.

They fuse with one another and form bone between two sheets of Mesenchyme which then condenses and develops into periosteum (the connective tissue surrounding bone).

4) Development of periosteum

Compact bone forms within Spongey bone.

Much of this Spongey bone will be remodelled into adult shape.

Front 5

What is Endochondral (chond- cartilage) ossification?

Back 5

STARTS WITH HYALINE CARTILAGE MODEL

All long bones form through this process.

Surrounded by Perichondrium made out of DICT- protects.

1) Development of cartilage:

Chemical messages cause cells to form in shape of future bone.

Cells develop into chondroblasts which secrete ECM of cartilage.

2) growth of cartilage:

Bony collar forms causing chrondroblasts to start dieing, send message to brain.

3) development of primary ossification centre:

Nutrient artery penetrates shaft and stimulates cells in the Perichondrium to differentiate into blasts to secrete ECM of bone. Regions where the bone tissue replaces cartilage grow toward the end of bone from Epiphyseal plate.

4) development of medullary cavity:

While Spongey bone is forming, osteoclasts break down the newly formed Spongey bone to form medullary cavity.

5) development of secondary ossification centre:

Secondary centres are forming where arteries have entered the Epiphyses of bones. Occurs around time of birth.

Process is similar except Spongey bone isn't broken down. Hyaline cartilage then becomes articular cartilage.

6) Formation of articular cartilage and Epiphyseal plate:

Hyaline cartilage makes up the Epiphyseal plate responsible for growth and remains here.