What Is the Endosteum?

A diagram of the anatomy of a bone, showing the endosteum.
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  • Written By: Constance Simmons
  • Edited By: Michelle Arevalo
  • Last Modified Date: 31 August 2014
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Endosteum is a soft, thin connective tissue that lines the inner cavity of long bones. It plays an important role in the healing of fractures by creating new cells necessary for the bone to fuse. This connective tissue also has hematopoietic potencies, which means that it contains haematopoietic stem cells (HSCs). HSCs are significant because they can create any type of blood cell.

There are a couple of medical terms used to describe the area of bone that contains endosteum. These include medullary cavity and medullary membrane. This membrane is found in the diaphysis, or shaft, of long bones. The walls of this cavity are made of cancellous bone, also called spongy bone. This is responsible for only 20-percent of the skeleton’s weight. The medullary cavity contains red and yellow bone marrow.

There are three different types of endosteum. They are cortical, osteonal, and trabecular. The name of each type refers to the area of the inner bone where it is located.

The cortical endosteum lines the cortical bone. It also forms the boundaries of the marrow cavity. This cavity contains yellow bone marrow, which stores fat cells for the body. In cases of extreme malnutrition these cells are used by the body to fuel itself.

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The trabecular endosteum covers the inner surface of trabeculae, which covers the spongy bone at the shaft. Trabeculae are bony bars that help the bone absorb contact without damage. They also contain red marrow, which contains HSCs and is responsible for creating new blood cells for the body.

Osteonal endosteum forms the lining of osteonal canals. These are found in compact bone and are home to the bone’s blood and nerve supplies. They are also known as Haversian Canals, after the physician who discovered them.

When an individual is malnourished, endosteum is reabsorbed by the body. Since it is part of the inner bone, a decrease results in less bone thickness and density. This thereby reduces the cortical thickness of the bone, which is devastating to the body because cortical bone is responsible for many bodily functions, including storing and releasing calcium. It can also reduce weight because cortical bone makes up about 80-percent of the human skeleton’s weight.

Periosteum is the equivalent to endosteum on the outside of the bone. It is durable and firm. Periosteum is also important in the healing of fractures because it produces cells needed to rebuild the bone.

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KoiwiGal
Post 3

It wasn't until I took a biology class on the structure of the skeletal system that I realized how complex our bones really are. They aren't just supports for our muscles and organs, they are living tissue just like every other part of the body.

One thing I found interesting was when our professor told us that the weight of the skeleton can vary over time depending on how much force it's subject to. So, if you are a heavy person, you'll end up with heavy bones as well (so that old saying "she's got big bones" has a kind of truth to it!).

He didn't go into it in depth, but it must be this part of the bone that increases, as it says in the article, it makes up most of the weight.

bythewell
Post 2

@pleonasm - I'm sure they are working toward being able to do this. I know they are with ordinary stem cells at least.

And I've heard there is some progress. From what I remember they are pretty good at getting the stem cells to turn into the cells that they want, although I don't know if that applies to HSCs particularly.

It would be fantastic for research too, you see. If you had what amounts to an infinite supply of blood cells you'd be able to test different medications on them without needing to worry.

Unfortunately, I don't think they have a foolproof way of making cells live in the lab, or they would have already eliminated the stem cell debate by simply making their own supply.

pleonasm
Post 1

If the endosteum contains haematopoietic stem cells, I wonder if it can be used to create blood for people. If they could make a sample of endosteum grow in a lab indefinitely, they could create as many of the HSCs as they wanted for each person.

And in turn they could stimulate those HSCs to become different kinds of blood cells.

It would eliminate the need for blood donors, and the very careful screening that needs to be done when people donate blood, in order to make sure they are disease free and that their blood type will match the person receiving the donation.

This would be invaluable, especially to people with rare blood types who might otherwise have difficulty finding donor blood.

And I assume it can also make marrow cells, which would be even more useful, because marrow extraction is so much worse than blood donation.

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