Osteogenesis (Bone Formation): Intramembranous Ossification (Nursing)

00:01 So now let's talk about bone formation.

00:04 The process of bone formation is referred to as ossification or osteogenesis.

00:11 There are four situations where bone formation will occur.

00:17 First, during embryological or fetal development.

00:21 Second, when you are growing or as your bones grow before adulthood.

00:28 Third, all throughout your life as your bones remodel.

00:33 And finally, in a situation where you have to heal a fracture.

00:41 So there are two forms of bone formation or ossification.

00:46 There is intramembranous ossification and then there is endochodral ossification.

00:52 Intramembranous ossification is usually associated with the formation of the flat bones like those in the skull.

01:00 Whereas, endochondral ossification is usually associated within formation of the other bones in the body, and specifically the long bones in the body.

01:11 So when it comes to intramembranous ossification or the formation of flat bones, there are four major steps.

01:21 In the first step, the mesenchymal cells, in the mesenchyme of the fetus, are going to create an ossification center.

01:31 These cells will then differentiate into osteoblasts cells.

01:37 These osteoblasts cells then secrete extracellular matrix including collagen fibers.

01:46 In the second step, as the osteoblasts are surrounded by the extracellular matrix that they secrete, they been differentiate into mature osteocyte cells.

01:59 These osteocytes are now housed inside of little areas called lacunae.

02:05 From their bone matrix begins to calcify.

02:12 The third step is now the formation of the outer portion of the bone or the periphery of the bone.

02:19 First, the mesenchyme is going to form a periosteum and the mesenchymal cells are now going to be replace with osteoblasts cells.

02:29 As well, in this step, we start to form the trabeculae which are the little projections that are found in spongy bone.

02:38 Also, blood vessels start to infiltrate through the holes that are found throughout the trabeculae.

02:47 And the final step of intramembranous ossification compact bone is starting to be formed toward the periphery of the bone.

02:57 The periosteum starts to form the fibrous periosteum layer on the outside of the bone.

03:03 And inside of the bone, the spongy bone begins to be filled with red marrow, as the red blood cells are starting to form marrow tissue.