BONE REMODELING

bone resting

activiation of quiescent, or resting bone

bone deposition process

how new bone is formed, a matrix of minerals and collagen fibers, called osteoid, is added to the newly formed bone cavity by the action of mature osteoblast cells. Osteoid is laid down between an area of unmineralized bone matrix, called an osteoid seam, and the area of old, mineralized bone.

Bone remodeling

constantly undergoing in bones, occurs in approximately 5% of total bone mass at any given time and occurs at varying rates in different regions of the body

osteoclast cells resorb a

discrete amount of bone, creating a groove as they move along the cell surface, breaking down the extracellular matrix

Bone remodeling particularly targets bone that is

injured, or areas where additional strength is required

bone resorption

loss of minerals and collagen fibers from bone tissue by the action of osteoclasts.

Osteoclast precursor cells are recruited to the activated surface, and fuse to form

mature, multinucleated osteoclasts.

bone deposition

occurs when new layers of bone tissue are formed

bone resorption

occurs when there is a loss of minerals and collagen fibers from bone.

Osteopregenitor cells/osteoblast precursor cells, are

recruited to the area, and subsequently proliferate and differentiate into mature osteoblast cells

proteoglycan

substance deposited by mononuclear cells, forming a cement line and release growth factors that initiate the bone formation phase of the remodeling cycle

in adult skeletons, compact bone is replaced every

10 years

in adult skeletons, spongy bone is replaced every

3-4 years

bone mineralization

Once embedded in the osteoid, osteoblast cells become trapped and mature into osteocytes.

2 processes of bone remodeling:

bone resorption and bone deposition

Layers of osteoid build up and subsequently mineralize, forming

new bone tissue

The dissolved minerals are then transported through the

osteoclast cell, along with the products from the digested matrix, and enter the blood via the interstitial fluid

bone remodeling 5 stages

bone resting, bone resorption, bone reversal, bone formation, bone mineralization

bone lining cells

inactive osteoblast cells cover all available surfaces of the resting bone

bone reversal occurs after

osteoclasts have completed their bone removal

The osteoblasts now lying on the surface of this newly formed bone once again become

quiescent, lining the cells until they become activated again at the start of another remodeling cycle

the osteoclast maintains contact with the surface of the bone, via its

ruffled border which secretes two destructive substances lysosomal enzymes that digest the matrix, and hydrochloric acid that breaks down the calcium salts in bone and converts them into a soluble form

Bone remodeling processes act together on the surfaces of

the periosteum and endosteum