bone remodeling

Examples of bone remodeling in the following topics:

• Stages of Bone Development

  • Although bone initially forms during fetal development, it undergoes secondary ossification after birth and is remodeled throughout life.
  • When a tooth is lost and not replaced, bone remodeling will fill in much of the socket.
  • Bone remodeling also occurs in response to trauma, such as that following accidental bone fracture or the placement of dental implants.
  • Osteoblasts and osteoclasts, coupled together via paracrine cell signalling, are referred to as bone remodeling unit.
  • The bone remodeling period refers to the average total duration of a single cycle of bone remodeling at any point on a bone surface.

• Bone Remodeling

  • Bone remodeling or bone turnover is the process of resorption followed by replacement of bone and occurs throughout a person's life.
  • Remodeling or bone turnover is the process of resorption followed by the replacement of bone with limited change in shape; this process occurs throughout a person's life.
  • Osteoblasts and osteoclasts, coupled together via paracrine cell signaling, are referred to as bone remodeling units.
  • The purpose of remodeling is to regulate calcium homeostasis, repair micro-damaged bones (from everyday stress), and to shape and sculpture the skeleton during growth .
  • The action of osteoblasts and osteoclasts are controlled by a number of chemical factors that either promote or inhibit the activity of the bone remodeling cells, controlling the rate at which bone is made, destroyed, or changed in shape.

• Bone Scans

  • Bone scans are a special type of nuclear scanning test that is often used to find bone cancer or bone inflammation.
  • A bone scan is a nuclear scanning test to find certain abnormalities in bone that are triggering the bone's attempts to heal.
  • A nuclear bone scan is a functional test, which means it measures an aspect of bone metabolism or bone remodeling .
  • Nuclear bone scans are not to be confused with the completely different test often termed a "bone density scan," DEXA or DXA, which is a low exposure X-ray test measuring bone density to look for osteoporosis and other diseases where bones lose mass, without any bone re-building (osteoblastic) activity.
  • The technique, therefore, is sensitive to fractures and bone reaction to infections and bone tumors, including tumor metastases to bones, because all these pathologies trigger bone osteoblast activity.

• Parathyroid Hormone

  • Parathyroid hormone maintains the body's calcium levels by increasing the absorption of calcium from the bones, kidneys, and GI tract.
  • PTH is a small protein hormone that is integral to the regulation of the level of calcium in the blood via the bone, kidneys, and intestines.
  • This interaction between parathyroid hormone and calcitonin is also an important part of bone remodeling.
  • This is a lifelong process where mature bone tissue is removed from the skeleton and new bone tissue is formed.
  • Parathyroid hormone acts on a bone to increase its blood calcium levels by stimulating osteoclasts to break down bone and release calcium into the bloodstream.

• Bone Repair

  • Substitution of the woven bone with lamellar bone precedes the substitution of the hyaline cartilage with lamellar bone.
  • This new lamellar bone is in the form of trabecular bone.
  • The remodeling process continues with substitution of the trabecular bone with compact bone.
  • Eventually, the fracture callus is remodeled into a new shape that closely duplicates the bone's original shape and strength.
  • The remodeling phase takes three to five years depending on factors such as age or general condition.

• Exercise and Bone Tissue

  • If loading on a particular bone increases, the bone will remodel itself and have time to become stronger to resist that sort of loading.
  • If the loading on a bone decreases, the bone will become weaker due to turnover.
  • It is less metabolically costly to maintain and there is no stimulus for continued remodeling that is required to maintain bone mass .
  • Astronauts who spend a long time in space will often return to earth with weaker bones, since gravity hasn't been exerting a load on their bones.
  • Their bodies have reabsorbed much of the mineral that was previously in their bones.

• Capacity of Different Tissues for Repair

  • While the bone formation usually spans the entire duration of the healing process, in some instances, bone marrow within the fracture has healed two or fewer weeks before the final remodeling phase.
  • This new lamellar bone is in the form of trabecular bone.
  • The remodeling process substitutes the trabecular bone with compact bone.
  • Eventually, the fracture callus is remodeled into a new shape that closely duplicates the bone's original shape and strength.
  • The remodeling phase takes three to five years depending on factors such as age or general condition.

• Bone Grafting

  • Bone grafting is a surgical procedure that replaces missing bone in order to repair bone fractures.
  • Bone grafts may be autologous (bone harvested from the patient's own body, often from the iliac crest), allograft (cadaveric bone usually obtained from a bone bank), or synthetic (often made of hydroxyapatite or other naturally-occurring and biocompatible substances) with similar mechanical properties to bone.
  • Most bone grafts are expected to be reabsorbed and replaced as the natural bone heals over a few months' time.
  • As native bone grows, it will generally replace the graft material completely, resulting in a fully-integrated (remodeled) region of new bone.
  • Bone grafting is also used to fuse joints to prevent movement, repair broken bones that have bone loss, and repair broken bone that has not yet healed.

• Bone and Calcium Homeostasis

  • Calcium release from bone is regulated by parathyroid hormone.
  • Calcitonin stimulates incorporation of calcium in bone.
  • It circulates as a hormone in the blood, regulating the concentration of calcium and phosphate in the bloodstream and promoting the healthy growth and remodeling of bone.
  • The resulting high levels of calcitonin in the blood stimulate the bone to remove calcium from the blood plasma and deposit it as bone.
  • Removal of calcium from the bone is also inhibited.

• Development of Joints

  • Articular cartilage is a flexible material found between bones at movable joints.
  • Cartilage growth generally refers to matrix deposition, but can include both growth and remodeling of the extracellular matrix.
  • The epiphysis is the rounded end of a long bone, at its joint with adjacent bone(s).
  • The region of the long bone that forms the joint is called Pressure Epiphysis.
  • Image shows the location of the epiphyseal plates (or lines) and the articular surfaces of long bones.