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Bone Development: Intramembranous Ossification

Bone Development: Intramembranous Ossification

Author: Aaron Mullally

- Define and apply the following terms to bone growth and development: lamellae, lacunae, canuliculi, Haversian systems, compact bone, cancellous bone, trabeculae

- Describe what the term mesenchyme means

- Identify what type/class of bone intramembranous ossification is used to form

- Describe the basic steps of endochondral ossification

- Describe how the design of a flat bone is essential to its role

- Identify that red bone marrow is found within flat bones & the proximal ends of the femur and humerus; also describe the role of red bone marrow

- Identify where you find flat bones and long bones of the body

In this packet you will dive into the topic of how flat bones develop from the embryo. You will also get some new terminology tossed your direction that will apply to more than this particular packet (remodelling, endochondral ossification, structure of bone, histology of bone).

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Overview of Intramembranous Ossification

There are two major processes that create bone during embryonic development, intramembranous and endochondral ossification. This packet will focus on intramembranous ossification.

Intramembranous ossification is the embryonic development of flat bones from an embryonic tissue called the mesenchyme. The word mesenchyme is a more or less a term used to describe embryonic connective tissue. There are four major steps that occur throughout this process that I will highlight here and elaborate more on in the video presentation below:

1) Formation of ossification centers: centrally located stem cells within the mesenchyme differentiate (specialize) into osteoblasts, forming the ossification center

2) Matrix formation: osteoblasts start to secrete the fibers (proteins) that make up the bony matrix, called osteoid. Soon after the osteoid will combine with calcium to form calcified bone. This calcified bone will engulf the osteoblasts which will make them form into osteocytes.

3) Periosteum and Weaving: The osteoid is continually laid down randomly around blood vessels. Structures called trabeculae (little beams) form around the vessels and pores are found where the blood vessels are located, thus forming spongy bone. The blood vessels on the outside of the spongy bone condense and form into the periosteum (outer vascular CT outside of bone)

4) Compact bone formation: as the trabeculae thicken within the spongy bone the osteoblasts on the periphery will continue to lay down osteoid. This osteoid will condense to form lamellar bone (compact bone) around the spongy bone (on both sides). As this process contines red bone marrow will start to appear where the blood vessels were located in the spongy spaces

Source: The mind of Aaron

Overview of Intramembranous Ossification

After reading the objectives and summary above watch this video to get a more visual experience on this topic.

Source: Self made with images from Marieb and

Terminology Slides

Slides from the presentation

Source: Self made