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
