What is the Difference Between Periosteum and Endosteum

The main difference between periosteum and endosteum is that the periosteum covers the outer surface of bones whereas endosteum covers the inner surface of bones. Furthermore, periosteum occurs in all bones except at the joints of long bones while endosteum occurs in all bones. Moreover, periosteum consists of two layers while endosteum is a thin layer.

Periosteum and endosteum are two connective tissue membranes which cover the lining of bones. Both of them contain cells including osteoblasts and fibroblasts.

Key Areas Covered

1. What is Periosteum
     – Definition, Structure, Function
2. What is Endosteum
     – Definition, Structure, Function
3. What are the Similarities Between Periosteum and Endosteum
     – Outline of Common Features
4. What is the Difference Between Periosteum and Endosteum
     – Comparison of Key Differences

Key Terms

Bone Lining, Bone Remodeling, Connective Tissue, Endosteum, Osteoblasts, Periosteum

What is Periosteum

Periosteum or periosteal surface is the connective tissue layer that covers the outer surface of bones. However, it does not occur at the joints of long bones. It is made up of dense irregular connective tissue. Also, the two main divisions of periosteum are the outer fibrous layer and the inner cellular or osteogenic layer. The fibrous layer consists of fibroblasts and collagen bundles. And, this layer provides attachment points for tendons and ligaments. Also, it contains blood vessels, lymphatic vessels, and nerves. Therefore, periosteum provides nourishment to the bones as well.

Figure 1: Periosteum and Endosteum

On the other hand, the cellular layer consists of osteoblasts, osteoprogenitor cells, and bone lining cells. These osteoprogenitor cells differentiate into osteoblasts responsible for bone remodelling.

What is Endosteum

Endosteum or endosteal surface is the thin connective tissue layer that covers the medullary cavity of all long bones. That means; endosteum occurs beneath the periosteum. Endosteum consists of only a cellular layer, which contains bone lining cells, osteoblasts, and osteoprogenitor cells. Therefore, the main function of the endosteum is to help in the bone growth, repair, and remodelling.

During a long period of malnutrition, endosteum is reabsorbed reducing the cortical thickness. However, the reabsorption of bones by osteoclasts prevents the unnecessary thickness of the endosteum.

Similarities Between Periosteum and Endosteum

• Periosteum and endosteum are two membranes which cover the lining of bones.
• Both are made up of connective tissue.
• Also, both contain cells including fibroblasts, osteoblasts, and osteoprogenitor cells.
• Besides, both structures play a key role in bone remodelling.

Difference Between Periosteum and Endosteum

Definition

Periosteum refers to a dense layer of vascular connective tissue enveloping the bones except at the surfaces of the joints while endosteum refers to a layer of vascular connective tissue lining the medullary cavities of bone. Thus, this is the fundamental difference between periosteum and endosteum.

Occurrence

The main difference between periosteum and endosteum is that the periosteum lines the outer surface of bones while endosteum covers the inner surface of the bone.

Present in

Moreover, another difference between periosteum and endosteum is that the periosteum is present in all bones except at the joints of long bones while endosteum occurs in all bones.

Thickness

Furthermore, the periosteum is a thick layer while endosteum is a thin layer.

Layers

Layers is also a difference between periosteum and endosteum. Periosteum consists of two layers: the outermost fibrous layer and innermost cellular layer while endosteum consists of a single cellular layer.

Role

Periosteum nourishes compact bones and provides sites for the attachment of tendons and ligaments while endosteum is important in the growth, repair, and remodelling of bones. Hence, this is another difference between periosteum and endosteum.

Conclusion

Periosteum is the thick, connective tissue membrane that covers the outer surface of the bones. It consists of an outer fibrous layer and inner cellular layer. In comparison, endosteum is the thin connective tissue layer that covers the medullary surface of bones. It only contains a cellular layer. Significantly, the periosteum is important in nourishing bones while both periosteum and endosteum are important in bone growth and remodelling. However, the main difference between periosteum and endosteum is their location and role in bone physiology.

References:

1. “37 6.3 Bone Structure.” ANATOMY AND PHYSIOLOGY, Pressbooks, 6 Mar. 2013, Available Here

Image Courtesy:

1. “607 Periosteum and Endosteum” By OpenStax College – Anatomy & Physiology, Connexions Web site. (CC BY 3.0) via Commons Wikimedia