The osteoclasts remove bone by dissolving the mineral and breaking down the matrix in a process that is called bone resorption. The osteoclasts come from the same precursor cells in the bone marrow that produce white blood cells.
When Paget's disease is active in several bones, the overactive osteoclasts can release enough calcium from the bone as they break it down to cause an elevated calcium level in the blood. This rare complication might cause fatigue, weakness, loss of appetite, abdominal pain, or constipation.
Osteoblasts work in teams to build bone. They produce new bone called "osteoid" which is made of bone collagen and other protein. Then they control calcium and mineral deposition. They are found on the surface of the new bone.
They are very active, motile cells and move around the resorbing surfaces of bone. Furthermore, osteoclasts frequently form clusters of cells during resorption and in histological sections of bone several may be seen occupying eroded depressions in the surface known as Howship's lacunae (Figure 2-5).
Low levels of calcium stimulates the release of parathyroid hormone (PTH) from chief cells of the parathyroid gland. In addition to its effects on kidney and intestine, PTH increases the number and activity of osteoclasts.
The total skeletal mass consists of two components: (1) an organic unmineralized matrix which includes mainly type 1 collagen and which comprises about one third of total bone weight and (2) the inorganic mineral phase of bone which constitutes about two thirds of the skeleton and is mainly composed of hydroxyapatite
According to the current knowledge, the main function of osteoclasts is to resorb mineralized bone, dentine, and calcified cartilage. However, their close relationship with immune cells as well as mesenchymal stem cells in a bone marrow environment may indicate also new, previously unrecognized functions.
With aging and after the menopause, an imbalance in bone resorption relative to formation results in negative bone balance at the tissue level. This may lead to osteoporosis, a common skeletal disease characterized by reduced bone mass, deterioration of bone microarchitecture, and increased susceptibility to fractures.
Osteoblast and osteoclast are the two main cells participating in those progresses (Matsuo and Irie, 2008). Osteoclasts are responsible for aged bone resorption and osteoblasts are responsible for new bone formation (Matsuoka et al., 2014). The resorption and formation is in stable at physiological conditions.
Molecules secreted by osteoblasts, osteocytes, and osteoclasts influence each other in a paracrine manner to maintain the balance of bone formation and bone resorption.
Osteoclasts dissolve bone mineral by massive acid secretion and secrete specialized proteinases that degrade the organic matrix, mainly type I collagen, in this acidic milieu.
While the osteoclasts resorb bone at various sites, other cells called osteoblasts make new bone to maintain the skeletal structure. During childhood, bone formation outpaces destruction as growth proceeds. After skeletal maturity is reached, the two processes maintain an approximate balance.
Bone is composed of four different cell types; osteoblasts, osteocytes, osteoclasts and bone lining cells.
During osteogenesis, osteoblasts lay down osteoid and transform into osteocytes embedded in mineralized bone matrix. That is, cells that continue to produce matrix actively bury cells producing less or no new bone matrix (passive burial).
10 Natural Ways to Build Healthy Bones
- Eat Lots of Vegetables. Vegetables are great for your bones.
- Perform Strength Training and Weight-Bearing Exercises.
- Consume Enough Protein.
- Eat High-Calcium Foods Throughout the Day.
- Get Plenty of Vitamin D and Vitamin K.
- Avoid Very Low-Calorie Diets.
- Consider Taking a Collagen Supplement.
- Maintain a Stable, Healthy Weight.
To destroy bone, osteoclasts use specific cell structures called podosomes, which are organized into rings by the actin cytoskeleton.
Estrogen Inhibits Osteoclastic Bone-resorbing Activity and Promotes Osteoclast Apoptosis Through ER-mediated Mechanisms.
Estrogen plays an important role in the growth and maturation of bone as well as in the regulation of bone turnover in adult bone. During bone growth estrogen is needed for proper closure of epiphyseal growth plates both in females and in males.
Prior to ovulation, the role of estrogen is considered to be important in the regeneration and growth of the endometrium and to prepare the tissue to respond to progesterone post-ovulation.
Taking estrogen can increase bone density and lower the risk of breaking bones. Estrogen alone is also called ET (estrogen therapy) and estrogen given with progesterone is also called HT (hormone therapy). The Food and Drug Administration (FDA) has approved ET and HT to prevent osteoporosis in postmenopausal women.
Estrogen deficiency not only accelerates bone loss in postmenopausal women but also plays a role in bone loss in men. Estrogen deficiency can lead to excessive bone resorption accompanied by inadequate bone formation. Osteoblasts, osteocytes, and osteoclasts all express estrogen receptors.
Estrogen is a sex hormone that is essential to female bone health because it promotes the activity of osteoblasts, which are cells that produce bone. When estrogen levels drop during menopause, the osteoblasts aren't able to effectively produce bone.
Testosterone is an important hormone for both bone gain and maintenance in men. Hypogonadal men have accelerated bone turnover and increased fracture risk.
Estrogen has multiple other effects that relate to the skeleton. For example, enhanced intestinal calcium absorption can be beneficial to bones. Estrogen protects the bone from the resorptive effects of PTH. Estrogens may interact with mechanical forces to build bone.
Estrogen, a hormone in women that protects bones, decreases sharply when women reach menopause, which can cause bone loss. This is why the chance of developing osteoporosis increases as women reach menopause.
What affects bone health?
- The amount of calcium in your diet. A diet low in calcium contributes to diminished bone density, early bone loss and an increased risk of fractures.
- Physical activity.
- Tobacco and alcohol use.
- Gender.
- Size.
- Age.
- Race and family history.
- Hormone levels.
Osteoclasts are specialised bone-resorbing cells. This particular ability makes osteoclasts irreplaceable for the continual physiological process of bone remodelling as well as for the repair process during bone healing.
Defects in osteoclast function, whether genetic or iatrogenic, may increase bone mass but lead to poor bone quality and a high fracture risk. Pathological stimulation of osteoclast formation and resorption occurs in postmenopausal osteoporosis, inflammatory arthritis, and metastasis of tumors to bone.
When we think of bones, a lifeless skeleton usually comes to mind, but our bones are a living organ that grows and changes shape throughout our life. Much of this shaping results from forces which press, pull and twist the skeleton as we move, and the biggest of these forces is caused by our muscles.
It may be important to note that while osteoclasts are derived from the hematopoietic lineage, osteoblasts are derived from mesenchymal stem cells.
Rheumatologists treat patients with age-related bone diseases. They can diagnose and treat osteoporosis. Endocrinologists, who see patients with hormone-related issues, also manage the treatment of metabolic disorders such as osteoporosis. Orthopedic surgeons may fix fractures.
