Three Types of Bone Cells: Osteoblasts, Osteoclasts, and Osteocytes in Bone Remodeling

There are three types of bone cells in bone marrow. Unless you have a fracture or a disease like osteoporosis, your physician may never talk about osteoblasts, osteoclasts, and osteocytes.

And thats OK. But if you are a anatomy and physiology student, youll need to understand the histology of these human bone cells and what they are used for in the body.

All are skeletal cells used in bone remodeling, but each has a similar but different role in the human skeleton. Well look at the differentiation of these 3 types of bone cells, along with process of bone growth and remodeling in this article.

Bony remodeling

Many people think bones are lifeless. Thats far from the truth.

Bones are living, dynamic organs that serve many functions. Functions include support, protection, aid in movement, being a reservoir for minerals such as calcium and phosphate, for hematopoiesis, and fat storage. They alter their composition through bony remodeling, which helps them maintain functions.

Mostly, though, bone remodeling takes place because of mechanical stress on the bones and through hormonal controls that maintain calcium levels in the blood.

The mechanical stress of running or even just walking and supporting our own weight creates microscopic damage to the bone.

If these microscopic damages are not repaired, its possible the damage could become larger, eventually causing a broken bone under minimal mechanical stress.

Hormonal control of bone remodeling is done mainly by the parathyroid glands, which produces parathyroid hormone.

This stimulates osteoclasts, which well discuss below, to begin their work as bone resorbing cells, sending calcium into the bloodstream.

Eventually, the blood-calcium level gets too high and triggers the PTH to stop. This will then cause blood-calcium levels to fall and trigger the process of bone remodeling again.

What is the meaning of osteoclasts and osteoblasts?

Before we discuss osteoclasts vs osteoblasts, lets break down some medical terminology about these two terms.

The root combining form for both words is oste/o, which means bone. (You may also see oss/i or osse/o all of which mean bone.)

Bone is a connective tissue, composed of a solid extracellular matrix and cells, including osteoclasts and osteoblasts

The suffixes of our two words are different, though. Blasts means embryonic a condition related to an early stage of development. Clasts means breaking down. As youll see, this does provide insight into the differences.

Osteoblast functions

An osteoblast is a cell that is generating new bone matrix i.e., a bone forming cell.

It does this by creating the organic component in bone, namely collagen.

As osteoblasts move along the bone matrix, they get stuck in the tissue and turn into osteocyctes.

This creates new bone growth and repair. It also strengthens your bones so they can handle the mechanical stress you put on them.

For example: Running is a weight bearing activity and it requires your body to engage in osteoblastic activity and bulk up the bones so they dont become injured.

Compare running with cycling. Cycling is not a weight bearing activity, which means osteoblastic activity is not needed.

The extra bulk would create a thicker bone and increase mechanical stress on the body, making it inefficient and unneeded.

The adage form follows function is apt if you consider that a bone grows or remodels itself based on the demands put on it, according to Wolffs law.

Osteoclast functions

An osteoclast is a multinucleated cell, derived from cells in bone marrow, that breaks down bone matrix.

Osteoclasts function by moving along a bone surface, channeling grooves with lysosomeal enzymes, breaking down the bone matrix. This creates a liquid calcium that is recycled back into the blood.

Now the next time you get a broken bone youll be able to talk with your doctor about the three different types of bone cells.

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