Steps of Intramembranous Ossification

Lesson Transcript
Instructor: Danielle Haak

Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

Bone forms in a process called ossification. There are two main types of ossification, including intramembranous. Read this lesson to learn about intramembranous ossification and the steps involved in this process. Updated: 09/23/2022

What Is Ossification?

Osteoblasts are cells that create new bone. Ossification is the formation of bone by osteoblasts. The process begins about six weeks after fertilization during an embryo's development and continues to about the age of 25. There are two primary processes that create bone: intramembranous ossification and endochondral ossification. But for this lesson, we'll focus on the intramembranous kind.

Intramembranous ossification is when bone develops from fibrous connective tissue called mesenchyme. This process produces flat bones, including bones in the skull and face, the pelvic bone, and the clavicle, to name a few.

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Steps of Intramembranous Ossification

Different sources categorize the steps slightly differently, but the process is the same. Let's outline the four steps of intramembranous ossification.

Step 1

First, stem cells in the mesenchyme develop into osteoblasts, which act as ossification centers, which form when mesenchyme cells can differentiate into either calcium-secreting osteoblasts or bone matrix-secreting osteoblasts, but both become like a bone-creation headquarters.

Step 2

Next, the bony, extracellular matrix is formed, called an osteoid. The osteoblasts developed during Step 1 secrete proteins that form this osteoid matrix. As it forms, osteoblasts become trapped inside it. Cells that reside within fully formed bone are called osteocytes. In other words, the difference between osteoblasts and osteocytes are just their location. During this step, osteoid combines with calcium to make up calcified bones.

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