Bone metabolism and Ca homeostasis Flashcards
are bones static or dynamic tissue
dynamic
List the layers in bone from outside to inside
- periosteum
- compact/cortical bone (made of osteons)
- spongy bone (trabeculae)
- endosteum
- medullary cavity
where are sharpey fibers
between periosteum and outer compact bone
explain the composition of bone
- 67% inorganic hydroyapatite
- 33% organic (mainly collagen type 1 but also structural proteins and growth factors + cytokines)
what are the 2 models of bone organisation?
- rod like collagen molecules, stacked with space between them (quarter staggered). hydroyapatite crystals in between the rods
- collagen fibrils in a helix with hydroxyapatite crystals
how is bone remodled
- osteoclasts degrade bone
- osteoblasts produce bone
- when osteoblasts become encased in bone they become osteocytes
function of osteoblasts
- bone formation
- synthesis of matrix proteins (type 1 collagen, octeocalcin, others)
- mineralization
- activation of osteoclasts via RANKL production
function of osteoclasts
bone absorption
RANK is activated by RANKL and this leads to differentiation of cells to osteoclasts
why are bones remodeled?
prevent crystallization of mineral salts and prevent against brittle bones and fractures
what is osteoporosis
when here is more bone reabsorption than formation
what is osteopetrosis
when more bone formation than reabsorption
what are the 3 forms of circulating calcium
- 10% complex with phosphate, bicarbonate, citrate
- 50% ionized (free)
- 40% protein bound non diffusible
IL6
promotes bone resorption
oestrogen
inhibit bone resorption
PTH and Vitamin D roles
low calcium=PTH stimulation=more Ca release from bone and less phosphate in body
VD= increase in Ca and phosphate. This is stopped by low phosphate levels
