The key difference between periosteum and endosteum is that the periosteum consists of an outer fibrous connective tissue layer and an inner osteogenic layer while the endosteum is the thin membranous coating that covers the internal surface of the bone.
Bones play an important role in anatomy and physiology. Out of the types of bones, the long bones are the most common bones found, and it is important to study the formation and development of the bone. Long bones have two main components; namely, compact bone and spongy bone. The compact bone is the dense and hard part of the long bone. The spongy bone is the tissue filled cavity of the bone which is comparatively less hard and contains the red bone marrow. The structure of the bone consists of anatomical structures such as the proximal and distal epiphysis, spongy bone, and diaphysis consisting of the medullary cavity, endosteum, periosteum, and the nutrient foramen.
CONTENTS
1. Overview and Key Difference
2. What is Periosteum
3. What is Endosteum
4. Similarities Between Periosteum and Endosteum
5. Side by Side Comparison – Periosteum vs Endosteum in Tabular Form
6. Summary
What is Periosteum?
Periosteum is the main outer lining of the bone. It constitutes an outer fibrous connective tissue layer and an inner osteogenic layer. Primarily, the fibrous layer composes dense irregular connective tissue. Accordingly, this connective tissue contains strong collagen fibres and fibroblast cells. Fibroblasts are special cells that involve in producing bone fibre. It is mainly a bone repair mechanism in response to injury.
Consequently, the main function of the fibrous layer is to connect the bones with other vital parts such as ligaments, joints and tendons. The fibrous layer is the most highly vascularized part of the periosteum and is a significant contributor to the blood supply of bone. Thus, it involves in providing nourishment to the growing bone. It also includes a rich neural network. The deep portion of the outer layer contains a fibroelastic layer that contributes to maintaining elasticity of the bone.
Figure 01: Periosteum
Moreover, the osteogenic layer plays an important role in bone calcification and remodelling. It consists of stem cells and osteoblast cells lining the surface of the osseous tissue. The presence of the osteogenic layer results in introducing hardness to the bone. Thus, the osteogenic layer makes up the hard part of the bone. Osteoblasts are the cells involved in the calcification process. Through the bone calcification process, the periosteum participates in bone remodelling and development process via the deposition of calcium by the osteoblast cells.
What is Endosteum?
Endosteum is a thin, soft, connective tissue that lines the cavity of long bones. Hence, it also acts as the coating for the compact inner bone and the trabeculae of the spongy tissue. The characteristic feature of the endosteum is the presence of osteoprogenitor cells. These progenitor cells upon maturity differentiate into mature osteoblasts.
Figure 02: Endosteum
Moreover, these progenitor cells also participate in formatting the bone-matrix. Endosteum also contains haematopoietic stem cells that are responsible for the production of blood cells.
There are three main types of endosteum, based upon its location.
- Cortical endosteum – endosteum found on the inner walls of cortical bone acts as the border of the marrow cavity.
- Osteonal endosteum – located on the inner walls of the osteonal canal of the compact bone.
- Trabaculae endosteum – lines the inner walls of the trabeculae.
Also, endosteum mainly involves in bone remodelling, growth and development process.
What are the Similarities Between Periosteum and Endosteum?
- Periosteum and Endosteum are two main parts of the bone structure.
- They are located in the diaphysis region of the bone.
- Also, both are involved in bone remodelling and development.
- Furthermore, they contribute to the hardness of the bone through the calcification process.
What is the Difference Between Periosteum and Endosteum?
Periosteum and endosteum are two main layers of the bones, especially in the diaphysis region. Periosteum lines the outer surface of the bone and inner osteogenic layer. On the other hand, endosteum forms the inner thin membranous coating of the bone cavity. Therefore, this is the key difference between periosteum and endosteum. Furthermore, periosteum consists of two layers; fibrous layer and connective tissue layer while the endosteum consists of one layer; connective tissue layer. Hence, it is also a difference between periosteum and endosteum.
Moreover, periosteum and endosteum differ from each other in the thickness as well. Accordingly, the thickness of periosteum is about 0.01 mm while the thickness of endosteum is about 0.1- 0-5 mm. Also, a further difference between periosteum and endosteum is that the periosteum has mature osteoblasts as their cell type while endosteum has fibroblasts and hematopoietic cells. The below infographic on the difference between periosteum and endosteum shows more details on these differences.
Summary – Periosteum vs Endosteum
Periosteum and endosteum are widely important in the process of bone remodelling and repair of bone upon injury to the bone. It is a continuous process which is rapid during the growth phase and slows down its rate over the ageing process. Hence, the periosteum mainly involves calcium deposition and providing nutrition to the growing bone. Thus, it involves maintaining the integrity of the bone. On the other hand, endosteum which is the inner lining involves in producing osteoblasts via progenitor cells to initiate the bone development process. Therefore, this is the difference between periosteum and endosteum.
Reference:
1. Dwek, Jerry R. “The periosteum: what is it, where is it, and what mimics it in its absence?” Skeletal Radiology, Springer-Verlag, Apr. 2010. Available here
2. “Endosteum.” Human Anatomy. Available here
Image Courtesy:
1.”624 Diagram of Compact Bone-new”By OpenStax College – Anatomy & Physiology, Connexions Web site. Jun 19, 2013., (CC BY 3.0) via Commons Wikimedia
2.”606 Spongy Bone”By OpenStax College – Anatomy & Physiology, Connexions Web site. Jun 19, 2013., (CC BY 3.0) via Commons Wikimedia