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
effect of calcitonin
is secreted when high Ca plasma levels, and causes less Ca absorbtion in intestine and less Ca resorption from bone by osteoclasts
high levels of calcitriol
inhibit transcription, because it binds to VD receptors and this affects transcription of genes (calbindin)
calcium sensing receptor CaSR
- present in parathyroid chief cells, thyroid C cells, kidney, brain
- is a GPCR of G-PLC and GS
- generates IP3
explain the PTH related protein
- binds PTH receptor
- lactation: is the hormone for mobilisation of Ca to the milk
- hypercalcemia of malignancy- in some lug cancers
explain calcitonin
product of parafollicular C cells of the thyroid
- inhibits bone resorption
- promotes renal excretion of Ca
abosrption of calcium is greater at
a low ph
list 7 factors that affect bone mass
- gender
- race
- genetics (estrogen receptor gene, type 1 collagen gene, vitamin D receptor gene)
- gonadal steroids (increases)
- growth hormone (increases)
- calcium intake
- exercise
