Summary of endosteum

Summary of Endosteum:

Definition :

The endosteum (plural endostea) is a thin vascular membrane of connective tissue that lines the inner surface of the bony tissue that forms the medullary cavity of long bones.

Iit also lines the Haversian canal and all the internal cavities of the bone.

This endosteal surface is usually resorbed during long periods of malnutrition, resulting in less cortical thickness.

The outer surface of a bone is lined by a thin layer of connective tissue that is very similar in morphology and function to endosteum. It is called the periosteum, or the periosteal surface. During bone growth, the width of the bone increases as osteoblasts lay new bone tissue at the periosteum.

 To prevent the bone from becoming unnecessarily thick, osteoclasts resorb the bone from the endosteal side.

Composition of endosteum:

The endosteum consists of a layer of flattened osteoprogenitor cells and a type-III collagenous fibers (reticular fibers).

 

 The endosteum is noticeably thinner than the periosteum.

Classification of endosteum:

 it  is classified into three types based on their site: (i) Cortical endosteum: endosteum lining the bone marrow cavity, (ii) Osteon endosteum: Endosteum lining the osteons mainly contains nerves and blood vessels. (iii) Trabecular endosteum: Lines the trabecula near the developing part of the bone. It plays a role in the growth and development of the bone.

Functions:

Endosteum plays a role in the formation of an internal matrix by absorption and deposition of tissue.

The endosteum stimulates the uninterrupted internal bone resorption. The medullary canal, along with the overall bone diameter, increases because of endosteum-stimulated resorption.

Endosteal endoblasts secrete bone matrix and compose ridges beside the periosteal blood vessels. The bony ridges expand and fuse to convert the groove into a vascularized tunnel.

 Endosteal osteoblasts compose new lamellae and form new osteons. Finally, a new circumferential lamella appears beneath the periosteum. This process repeats for continuous bone diameter enlargement, which slows down with adulthood

Bone modeling and remodeling: Periosteum, endosteum, and its cells play a critical role in modeling and remodeling. 

Bone modeling and remodeling: Periosteum, endosteum, and its cells play a critical role in modeling and remodeling. 

• Bone remodeling is a process where osteoclasts and osteoblasts work sequentially to reshape and renew bone; the process continues throughout life. It divides into four phases; (a) recruitment and activation of osteoclasts, (b) resorption of old bony tissue, (c) apoptosis of osteoclasts, and activation of osteoblasts (d) laying of new organic matrix and mineralization.
• Bone modeling is a process to shape the bone during growth, development, and healing. Mechanical factors like stress, strain, tension, muscular attachment, etc. play an important role in bone modeling. Osteoblasts and osteoclast play an independent role in bone modeling.