Full transcript
0:00So now let's talk about bone formation.
0:03The process of bone formation is referred to as
0:06ossification or osteogenesis.
0:11There are four situations where bone formation will occur.
0:16First,
0:17during embryological or fetal development.
0:21Second,
0:22when you are growing
0:23or as your bones grow before adulthood.
0:27Third,
0:28all throughout your life as your bones remodel.
0:33And finally,
0:34in a situation where you have to heal a fracture.
0:40So there are two forms of bone formation or ossification.
0:46There is intramembranous ossification
0:48and then there is endochodral ossification.
0:52Intramembranous ossification is usually associated
0:55with the formation of the flat bones like those in the skull.
0:59Whereas, endochondral ossification
1:02is usually associated within formation of the other bones
1:05in the body,
1:06and specifically the long bones in the body.
1:11So when it comes to intramembranous ossification
1:14or the formation of flat bones,
1:17there are four major steps.
1:20In the first step,
1:22the mesenchymal cells, in the mesenchyme of the fetus,
1:26are going to create an ossification center.
1:30These cells will then differentiate into osteoblasts cells.
1:36These osteoblasts cells then secrete extracellular matrix including
1:42collagen fibers.
1:45In the second step,
1:47as the osteoblasts are surrounded
1:50by the extracellular matrix that they secrete,
1:53they been differentiate into mature osteocyte cells.
1:58These osteocytes are now housed inside of little areas
2:02called lacunae.
2:05From their
2:06bone matrix begins to calcify.
2:12The third step is now the formation of the outer portion of the bone
2:16or the periphery of the bone.
2:18First,
2:19the mesenchyme is going to form a periosteum
2:22and the mesenchymal cells are now going to be replace
2:26with osteoblasts cells.
2:28As well, in this step,
2:30we start to form the trabeculae
2:33which are the little projections that are found in spongy bone.
2:37Also, blood vessels start to infiltrate
2:41through the holes that are found throughout the trabeculae.
2:47And the final step of intramembranous ossification
2:51compact bone is starting to be formed
2:53toward the periphery of the bone.
2:56The periosteum starts to form the fibrous periosteum layer
3:01on the outside of the bone.
3:03And inside of the bone,
3:04the spongy bone begins to be filled with red marrow,
3:09as the red blood cells are starting to form marrow tissue.