Bone Physiology Flashcards
hypocalcemia
hyperexcitablity
hypercalcemia
depressed activity
what triggers as result of low calcium
PTH secretion
four functions of PTH
- increased bone resorption
- increased kidney reabsorption
- block phosphate reabsorption
- stimulate conversion 25OH VitD to 1,25OH VitD
why is P excretion help with Ca absorption
if their levels rise together
-they will precipitate out
if want calcium up we need P down
role of 1,25OH VitD
- calcium reabsorption of gut
- stimulate P reabsorption
- allows mineralzation
- shuts off its own synthesis (negative feedback)
what happens in a loop
absorption and mineralization
where is 25OH Vit D converted to 1,25OH Vit D
kidney
insufficient 1,25 Vit D levels lead to what?
poor mineralization and impaired calcium absorption
calcitriol
1,25OH VitD
calcitonin
tumor marker
FGF23 absence?
hyper-P and hyper-Ca
markers for bone formation
alkaline phosphatase
osteocalcin
procollagen peptides (PINP/PICP)
markers of bone resorption
urinary hydroxyproline
NTX/CTX or N-telopeptides/C-telopeptides
pryidinoline
deoxypyridinoline
scurvy
Vit C deficinency (ascorbic acid)
- cannot crosslink collagen
- fragile bones
bone growth during childhood
growth of cartilage > endochondral bone formation
increase in bone width?
periosteal apposition
bone modeling
net bone formation
-two processes uncoupled
remodeling
coupled process where resorption followed by bone formation
no net gain in bone
osteoblast activity
lay down collagen and noncollagen proteins
mineralization of bone?
delayed a few days to allow cross linking
released by osteoblasts during bone formation?
osteocalcin and alkaline phosphatase
signal for osteoclast activity?
PTH > osteoblasts > activate osteoclasts
calcitonin receptor?
inhibitory for osteoclasts
PTH on osteoblasts?
causes release of M-CSF
-differentiation to osteoclast progenitors of hematopoietic stem cells
osteoblast affect on osteoclasts?
RANK-L by osteoblasts binds RANK on osteoclasts - triggers activity
OPG
osteoprotegerin
-inhibits bone resorption of osteoclast
soluble receptor for RANK-L
Vitamin D
necessary for mineralzation of bone
PTH
signals osteoblasts to activate osteoclasts (resorption)
calcitonin
inhibits bone resorption (osteoclasts)
hormones increasing bone formation?
growth hormone
thyroid hormone
insulin
gonadal hormones
hormones increasing bone resorption?
glucocorticoids
- suppress GI absorption
- induce osteoclastogenesis
- deplete osteoblasts
prostaglandins
stimulate bone resorption
DEXA scan and T scores?
can measure bone density
> -1 normal
-1 to -2.5 osteopenia
<-2.5 osteoporosis
bone biopsy
give architectural structure
risk factors for osteoporosis?
- modifiable
- nonmodifiable
modifiable
- age
- race
- gender
- menopause
- build
- family Hx
nonmodifiable
- Ca intake
- Vit D intake
- estrogen deficiency
- sedentary
- smoking
- alcohol
- caffeine
- meds
two drugs for osteoporosis?
antiresorptive and anabolic
antiresorptive drugs?
bisphosphonates
anabolic drugs?
intermittent PTH
osteomalacia
aka rickets
disorders in mineralization
-deficiency in Vit D
Pagets disease
excessive osteoblast activity
-treatment - bisphosphonates
extremely elevated alkaline phosphatase?
sclerotic phase of pagets
osteogenesis imperfecta
brittle bone disease
weakening of bone due to mutations in collagen leading to fractures and deformity
OI type I
most common
autosomal dominant
-one allele of alpha-1 procollagen is missing
OI type II
more rare
point mutation of COL1A1
-extreme bone fragility and death
osteopetrosis
marble bone disease
defective osteoclastic resorption
prolia
denosumab
monoclonal antibody for RANK-L
blocks bone resorption
benefit to combining antiresorptive and anabolic?
no
how to inhibit bone formation?
inhibit bone resorption by using bisphosphonates
