Bone tissue remodeling corresponds to bone remodeling that occurs permanently within bone tissue. Bones are adapted to current loading conditions by the remodeling processes of osteoclasts and osteoblasts. Excessive bone remodeling characterizes Paget’s disease.
What is bone tissue remodeling?
Bone tissue remodeling corresponds to bone remodeling that occurs permanently within bone tissue. Bone tissue damage is reversible. For example, revision of bone tissue damage aims to remodel bone tissue, which is also known as bone remodeling or bone tissue remodeling. During this process, old bone tissue is broken down and subsequently compensated for by newly formed bone by osteoblasts. Through the processes of bone tissue remodeling, the human organism maintains a stable skeletal system. If the repair mechanism did not exist, the human skeleton would show rapid signs of wear. The everyday stress on the bones is great. This stress always leaves structural damage in the bone tissue, which is compensated by the remodeling processes. Remodeling of bone tissue also responds to changes in loading conditions and adapts the structure of the bones to current stresses. Bone remodeling not only helps the skeleton withstand changing loads, but also plays a critical role in fracture healing. For example, the processes of remodeling replaced the callus of a healed fracture with fully functional hard bone.
Function and task
The process of bone tissue remodeling is a permanent body process. Bones, although so solid, are not a rigid and static structure, but permanently adapt to changes in external conditions. Each year, for example, about three of the cortical bone and about a quarter of the trabecular bone are remodeled. In about ten years, the entire bone mass of a person is thus completely broken down and rebuilt once. Bone remodeling simultaneously requires the presence and activity of bone-degrading osteoclasts and bone-building osteoblasts. For this reason, the process of bone tissue remodeling relies on some control, also known as coupling. The exact process of coupling has not yet been conclusively investigated. The bone-building osteocytes are thought to play an important role in the control. The same applies to parathyroid hormone, which stimulates the differentiation of osteoclasts and at the same time has a stimulating effect on osteoblasts. Vitamin D and cytokines, such as osteoprotegerin or RANKL, also play an important role in the control of bone remodeling. In adult humans, bone remodeling consists of relatively equal parts of resorption and new synthesis. In people in the growth phase, buildup exceeds breakdown. From postmenopause onward, resorption exceeds new synthesis in bone remodeling. Bone is the largest body reservoir of calcium and phosphates in addition to its support and mobility functions. For this reason, bone tissue remodeling is also often associated with a regulatory function in the homeostasis of calcium and phosphate. The mechanism of bone tissue remodeling takes place permanently and therefore does not need to be specially started when calcium or phosphates are needed. For this reason, the organism is able to react relatively quickly to fluctuations in the balance of the two substances. Thus, if the calcium level in human blood is too low, rapid compensation is possible thanks to bone remodeling.
Diseases and ailments
Bone remodeling depends, among other things, on a person’s age. Thus, for example, it is not necessarily to be evaluated as a pathological phenomenon if redmodeling in old age manifests itself predominantly as resorption and only inferiorly as new synthesis of bone tissue. Rather, the physician refers to this phenomenon as a change caused by the physiology of aging. The high proportion of new bone synthesis and the low proportion of resorption in the growth phase must also be regarded as age-physiological. Nevertheless, the remodeling of bone tissue can also be affected by pathological changes.For example, if significantly more tissue is resorbed than is newly synthesized, irrespective of older age, this phenomenon may well be related to diseases. One of these is tumor-related bone resorption, which is one of the complications of bone metastases. The bone is destroyed in this phenomenon, which results in an uncontrolled release of calcium. The calcium causes the calcium level in the blood to rise above the normal level. In this way, the kidney sometimes receives more calcium than the organ is able to excrete. Due to these interactions, many patients with malignant tumors therefore suffer from hypercalcemia. Paget’s disease is also sometimes manifested by bone remodeling. It is a disease that results in excessive remodeling of bone tissue. The increased remodeling can deform the bones and change the structure so that the bone becomes susceptible to fracture. At the beginning of its course, Paget’s disease manifests itself in abnormally high osteoclast activity. In isolated cases, pain occurs. In other cases, the disease remains asymptomatic for a long time and is therefore rarely diagnosed at an early stage. In the course of the disease, the increased bone resorption of the osteoclasts is followed by an overactivity of the osteoblasts, which attempts to compensate for the resorption processes. The compensation attempts of the osteoblasts result in an uncoordinated and excessive growth of bone tissue and usually correspond to undermineralized bone growth. For this reason, frequent bone fractures are expected in late Paget’s disease.
