Chapter 6: Osteoblasts, osteocytes, and osteoclasts
osteoblasts
stages: proliferation, maturation and extra-cellular matrix synthesis, and matrix mineralization
osteocytes osteoclasts
the process of reabsorption occurs when - activate -
osteocytes
as we age - die, leaving empty spaces, and making elderly more prone to fractures
osteocytes
in healthy bone tissue, - respond to mechanical stressors placed on the surface of the bone, making them a form of mechonosensory cells
ostoblasts
- secrete these things that contribute the the formation of osteoid, the softer, organic part of bone matrix: -type 1 collagen fibers -proteoglycans -non-collagen proteins such as osteocalcin -IGF-1 -alkaline phosphate (none are minerals)
osteoid
-also called ground substance -gelatinous, glue-like substance that attracts calcim and phosphate
osteocytes
-composed about 90% of all bone cells in mature, adult bones -longest lived bone cells that last decades
osteoblasts
-derived from mesenchymal stem cells -found in compact and spongy bone of all bones
osteoblasts cytokines
-play a role in the differentiation and reabsorption activity of osteoclasts by secreting cellular signals knows as -
osteoblasts
-polar clls -produce productes ->many proteins and collagen -large rER and golgi complex
calcium and phosphate
-represent the inorganic portion of an osteoid and cause it to harden, forming ossified bone -also referred to as hydroxyapatite
ossified bone
40% organic function and 60% inorganic function
osteoclasts
bone degrading cells
wolfe's law
bones may widen or change axis by addition or removal of bone tissue to or from appropriate areas and surfaces -requires coordination between osteoblasts/cytes/clasts and is regulated by the endocrine system
osteoclasts
derive from macrophages
osteocytes osteoblasts
exercising on a hard surface mechanically stresses the bone because muscles pull against them in order to contract. In response and with time, the bone becomes reinforced as - trigger the proliferation and activity of -
osteoclasts
inject hydrochloric acid into ossified matrix, lowering the pH to about 4.5, effectively dissolving the bone. -only known cell that can reabsorb mature bone
matrix mineralization osteocytes
last stage where osteoblasts become stuck in their own products and become stuck. When this happens, they get a new identity and become -
osteocytes
metabolically inactive cells embedded in bone matrix -spider-like appearance with denditic-like arms that radiate into the canaliculi and appear to almost touch neighboring osteocytes
balanced
osteoblasts activity is carefully - with the activity of osteoclasts -many diseases can occur when this - is off ->osteoporosis, osteoarthritis, and perhaps rheumatoid arthritis
bone remodeling
process begins with the removal of mature, mineralized bone tissue by osteoclasts. Their degradarive abilities allow osteoblasts to enter and secrete osteoid. Upon the osteoblasts becoming trapped in their own osteoid, new osteocytes are formed.
carbon dating
process used to estimate the age of a bone sample -relies more on the soft, organic fraction of osteoid instead of osteoid instead of the hardened, crystallized structure that is hydroxyapatite -hydrox. leaves itself open to contamination from groundwater
sequence of events
production of osteoblasts from MSCs->maturation of osteoblasts->production of osteoid and mineralization->trapping of osteoblasts withing this matrix, maturation of osteocytes and maintenance of bone, bone lining cells on surface->(decision pt.)-> signals from existing osteoblasts and osteocytes stimulate osteogenic differentiation of MSCs->beginning
osteoclasts
purpose is to degrade dead or dying chondrocytes in juveniles as well as degrade mature, mineralized bone in bone juveniles and adults
haversion canals
resorption of mature bone leaves pits and channels; in compact bone, reabsorption cuts new -
osteoblasts
responsible for bone formation -secrete bonematrix and play a major role in the calcification of the matrix