Body processes

Osteolysis – Function, Task & Diseases

Osteolysis

Osteolysis is the process of bone breakdown. This usually takes place as part of normal metabolism . However, if the balance between bone resorption and bone formation is disturbed, pathological loss of bone substance can occur.

What is osteolysis?

Osteolysis is the scientific term for bone resorption , which is a normal and necessary process in bone metabolism. During this process, bones are constantly being remodeled by breaking down existing bone substance and rebuilding it elsewhere. Bone metabolism is regulated hormonally.

There are two cell types in bone. These are the osteoblasts on the one hand and the osteoclasts on the other . Osteoblasts are responsible for bone formation. After mineralization , they transform into osteocytes (bone cells) that are no longer capable of dividing.

Osteoclasts, in turn, control bone resorption. These are multinucleated cells that have transformed into macrophage-like cells through the merger of stem cells from the bone marrow . Their task, as so-called scavenger cells, is to dissolve the bone substance. There are two forms of osteolysis. This is on the one hand the osteolysis in the context of bone remodeling and on the other hand the circumscribed osteolysis.

Bone remodeling is a general process in which there is a balance between bone loss and bone formation. In the case of circumscribed osteolysis, local bone loss takes place, but this is pathological.

function & task

Osteolysis is a necessary process in the organism, which simultaneously fulfills various functions. During bone remodeling, bone substance must constantly be broken down and rebuilt elsewhere. This is referred to as bone tissue remodeling. 

The bone and skeletal system is the body’s largest supporting organ. The constant strain on this support system leads to structural damage within the bones, which must be compensated for at any time in order to keep the musculoskeletal system functional. This only works through the continuous breakdown of damaged bone and the build-up of new bone.

Furthermore, this process also keeps the calcium and phosphate levels constant at the same time. The skeletal system represents the largest calcium and phosphate reservoir.

If, for example, too little calcium is supplied through food, increased bone loss occurs. In this way, fluctuating calcium and phosphate levels can be quickly compensated.

Overall, the bone and calcium metabolism is subject to hormonal regulation. The parathyroid hormone ensures a constant level of calcium in the blood by causing increased bone resorption by stimulating the osteoclasts. At the same time, if the calcium level in the blood is too high, it also affects the osteoblasts, which are responsible for bone formation.

In a healthy, adult person who is still fertile, there is a balance between bone resorption and bone formation. This constant bone remodeling process ensures a healthy musculoskeletal system.

Diseases & Ailments

If the balance between osteolysis and osteogenesis (bone formation, also known as ossification) is disturbed, damage to the bone structure occurs. With these disorders, the relationship between bone resorption and bone formation is usually shifted in favor of bone resorption. In very rare cases, however, the reverse relationship also occurs, with bone formation predominating over bone resorption. This is the case, for example, with genetically determined osteopetrosis (marble bone disease). 

The more common cases of general bone loss are due to a variety of causes. The balance can shift, among other things, due to the reduced activity of the osteoblasts, which disrupts the bone formation process. Due to the normal process of osteolysis, however, general bone resorption still takes place.

Furthermore, osteolysis can be increased in rheumatic processes, hormonal disorders ( hyperparathyroidism ), osteoporosis or metastases on the bone. General osteoporosis also always occurs in old age. Bone formation slows down here, while bone resorption is accelerated at the same time, often due to a lack of minerals as a result of resorption disorders. Hormonal causes of osteoporosis are often found in postmenopausal women .

In addition to osteoporosis, osteomalacia can also occur. While the entire bone substance, which is made up of organic and mineral components, is broken down in osteoporosis, only the mineral component is lost in osteomalacia. The cause here is often insufficient calcium incorporation into the bones, a lack of vitamin D or a disturbed phosphate metabolism .

In addition to the disruption of the balance between bone formation and bone resorption in the context of general bone remodeling, there is also the circumscribed osteolysis. Circumscribed osteolysis is always pathological and describes local bone loss due to local osteoclast overactivity without increased osteoblast activity. This means that there is local degradation of bone substance, which is no longer reproduced. Circumscribed osteolysis occurs, among other things, in the case of inflammatory processes, local tumors or metastases on the bone in the case of foreign tumors or constant foreign body contact with the bone. For example, implants , endoprostheses or osteosynthesis(surgical connection of several bones) can lead to osteolysis, which can ultimately lead to loosening of the prosthesis . The same applies to dental implants , which can lead to destruction of the jawbone if there is constant external contact .

As a result of chronic polyarthritis , bone cysts can appear near the affected joints . These bone cysts are cavities created by osteolysis. Local bone marrow suppuration caused by a bacterial infection can also lead to osteolysis.

A very rare disease is the so-called Gorham-Stout syndrome . This is where the bone completely dissolves, which then turns into lymphoid tissue. The cause of this disease is currently unknown.

Lisa Newlon
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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.