WHAT IS THE ENDOSTEUM? CHARACTERISTICS, FUNCTIONS AND TYPES - ANATOMY AND PHYSIOLOGY - 2025

The endosteum is the structured membrane that lines the walls of the medullary cavity of the bony trabecula (the spongy part of the bone), the haversian canals, and the inner walls of the long compact bones.

It can be defined as the thin layer of connective tissue that covers both the compact internal part of the bone and the spongy internal part of the bone.

This membrane is made up of bone connective tissue and a layer of osteoprogenitor cells that allow it to participate in the process of osteogenesis or regeneration of bone tissue.

These cells are known as preosteoblasts, and they are divided into two main types, osteoblasts and bone lining cells (Glossary, 2017).

The osteoblasts located in the endosteum are often known as endostial cells, and their main function is to form bone cells that contribute to the growth and regeneration process of the bones in the event of trauma or fracture in the bones. themselves.

On the other hand, the endosteum, together with the periosteum, is responsible for stimulating the growth of bones.

The endosteum is also believed to have hematopoietic properties. This means that it can stimulate the production of hematopoietic cells.

These cells are those that can transform any type of cell in the body into blood cells such as white, red blood cells or platelets (Fixit, 2014).

Endosteal functions

Different researches have shown that endosteum has osteogenic properties, which means that it directly contributes to the growth and repair process of bones.

In fact, the endosteum, in conjunction with the periosteum, is responsible for healing different types of fractures.

The endosteum has an important reparative function, especially after collecting samples from the bone marrow. This is due to the fact that in these types of situations the bone mesh that makes up the bone (known as the trabecula) is damaged during the sample collection process.

For this reason, the endosteum must contribute to the mesh repair process, by increasing the production of tissue regenerating cells, known as osteoblasts and osteoclasts.

On the other hand, it is believed that the endosteum also has hematopoietic properties, that is, it has the ability to stimulate the production of hematopoietic cells.

Hematopoietic cells are those that can transform any type of cell in the body into blood cells (Modric, 2013).

Additional endosteal tasks

Apart from the aforementioned functions of the endosteum, it fulfills other tasks of vital importance for the support of the bone tissue of the body.

Stimulates bone growth

Despite being a thin layer of connective tissue, the endosteum is responsible for stimulating the diametrical growth of the bones. This is possible thanks to the stimulation of the osteoblasts present in the cortical endosteum.

Reshape the bones

The endosteum plays a fundamental role in the reabsorption of bone tissue. In this sense, it works hand in hand with the periosteum to stimulate the growth and regeneration of reabsorbed bone tissue.

Repair bones

In the case of a fracture, the endosteum contributes to the repair process of the fracture. When a hematoma occurs within the bone, osteoblasts reproduce to contribute to callus formation (Doctor, 2016).

Endosteal location

The endosteum is located on the inner surface of the bone. It is the membranous layer that lines the medullary cavity, the bony trabecula (the spongy part of the bone), the Haversian canals and the internal walls of the long compact bones.

The endosteum can be found in bones such as the femur and humerus, in flat bones (such as the hip), in the rib cage (ribs), and in the patella.

In the case of the skull, the endosteum is located as a lining within different cavities.

Types of endosteum

There are three different types of endosteum:

Cortical endosteum

The cortical endosteum has the function of lining the cortical bone wall. In this way, it separates the cavity of the bone marrow from the other structures of the bone.

Osteonal endostium

The osteonal endosteum has the function of internally covering the osteonal channels.

Trabecular endosteum

The trabecular endosteum is the one that covers the bone mesh or bone trabeculae.

Clinical importance of the endosteum

The chemical exchange between the bone marrow and the blood vessels is made possible by the osteoblasts present in the endosteum.

On the other hand, endosteal cells are essential for the growth, repair and remodeling of bones. In this sense, if the endosteum did not exist, it would be impossible for the body to regenerate bone tissue after a fracture.

There are some parts of the bone matrix that are not completely covered by the endosteum. These uncovered parts are the places where osteoblasts and osteoclasts are located.

From there, these cells can deposit or remove bony components from the bone matrix, in order to regenerate tissue.

The endosteum, together with the periosteum, contributes to the repair and reconstruction of the bones after they suffer some trauma.

In this sense, the blood vessels and surrounding tissue of the injured area bleed and eventually form a clot around the edges of the trauma or fracture (Cediel, Cárdenas, & García, 2009).

When this happens, the endosteal cells go into an agile process of mitosis and reproduce in an accelerated way.

These new cells then migrate close to the affected area and begin to form new bone tissue. This bone tissue serves as a bridge to stabilize the trauma or fracture.

Endosteal-related diseases

In case a spinal injury develops in the inner part of the cortical bones, especially in the long bones, it can be observed that the endosteum takes on a wavy shape.

Although spinal injuries usually grow slowly and are sometimes not serious, rippling of the endosteum is always associated with a malignant condition.

Some of the malignant conditions that can occur in the body when the endosteum ripples can be enchondroma, osteomyelitis, chondromyxoid fibroma, skeletal amyloidosis, periprosthetic osteolysis, brown tumor, chondrosarcoma, multiple myeloma, and skeletal metastasis.

References

1. Cediel, JF, Cárdenas, MH, & García, A. (2009). 4.2. Periosteum and Endostium. In JF Cediel, MH Cárdenas, & A. García, Manual of histology: Fundamental tissues (pp. 182 - 183). Bogota DC: Universidad del Rosario.
2. Doctor, BB (2016). Bye bye Doctor. Obtained from Endosteum: byebyedoctor.com
3. Fixit, H. (August 3, 2014). Health Fixit. Retrieved from Endosteum: Definition and Functions: healthfixit.com
4. Glossary, H. (2017). Pub Med Health. Obtained from Endosteum: ncbi.nlm.nih.gov
5. Modric, J. (December 12, 2013). eHealthStar. Obtained from Endosteum: ehealthstar.com.