B6.052 - CBCL Osteoporosis Prework 2 Biology of Bone Flashcards
what makes up bone
organic matrix - 35% inorganic salts - 65%
what makes up organic matrix
EC organic phase, composed of proteins, glycoproteins, proteoglycans synthesized by osteoblasts consists of type 1 collagen fibers embedded in amorphous ground substance
inorganic matrix
hydroxyapatite crystals
osteoprogenitor cells
pluripotential, stem cells originating from mesenchyme. Differentiate into osteoblasts Found in periosteum and endosteum
osteblasts
synthesize and secrete organic matrix of bone: collagenous (type 1) and non collagenous and alkaline phosphatase that initiates calcification
osteocytes
osteoblasts that have entrapped themselves in calcified matrix. Alive and play critical role in maintenance and metabolism
osteoclasts
giant, multinucleated cells derived from monocytes. Do not function like vacuum cleaners but rather produce an acidic environment ideal for dissolution of bone matrix. Cell membrane of osteoclasts is thrown into folds and villous like processes constituiting ruffled border
origin of bone cells
mesenchyme –> osteoprogenitor cells –> osteoblasts –> osteocytes bone marrow –> monocytes –> osteoclasts
what doe osteoblasts synthesize
osteoid (type 1 collagen and proteoglycans) alkaline phosphate non coll proteins (RANKL, OPG, Osteocalcin, osteopontin, GFs)
what does osteoprotegerin do
a decoy receptor for RANKL (OPG)
what does osteocalcin do
required for mineralization
what does osteopontin do
formation of sealing zones
what do osteocytes do
assist in maintenance of calcium and phosphate ion levels in the blood stress sensors, mechanotrsansduction, synthesize sclerostin which inhibits osteoblastic activity
1 - osteoblasts
2 - osteoprogenitor cells
3 - osteoclast
4 - osteocytes trapped in bony matrix
