Bone Homeostasis Flashcards
PTH on bone
⬆️activity and number of osteoclasts ➡️release of calcium and phosphate
what stimulates PTH secretion
fall in plasma ionized calcium level
PTH on kidney
⬆️tubular resorption of calcium and magnesium
⬇️absorption of phosphate, amino acid, bicarbonate, sodium chloride and sulfate
stimulation of 1,25 DH vit D
metabolic active form of vit D
1,25 OH2D
enzyme that catalyzes formation of 1,25 OH2D from 25 OHD
1 hydroxylase
PT gland contains
ca sensitive protease
ca sensing receptor
vit D receptor and CYP27B1
ca sensitive protease
cleaves PTH
ca sensing receptor
reduces PTH production when stimulated by Ca
vit D receptor and CYP27B1
produces active metabolite of vit D, ⬇️PTH
1,25 DH vit D on bone
release of calcium and phosphate
1,25 DH vit D on intestine
⬆️Ca absorption
1,25 DH vit D on kidneys
reabsorption of calcium and phosphate
phosphaturic hormone
FGF 23
fibroblast growth factor 23
FGF 23 on kidney
inhibits phosphate reabsorption
inhibits 1,25 DH vit D production
FGF 23 on phosphate level
hypophosphatemia
➡️inhibition or defective mineralization of bone
primary site of production of FGF 23
osteoblasts
osteoclasts
low 1,25 DH vit D level impact by FGF 23
absorption of calcium thus there will be lower levels of calcium
phospate on PTH
regulates PTH secretion : form complexes with ca➡️ ⬇️Ca stimulates PTH secretion
high phosphate levels stimulate
FGF 23 production➡️
phosphate excretion
recombinant human PTH
only FDA approved bone forming drug
TERIPARATIDE
TERIPARATIDE on bone
stimulates the osteoblasts to induce RANK ligand that acts on osteoclasts and precursors to increase their number and activity
TERIPARATIDE on kidneys
increases reabsorption of calcium and magnesium
decreasing the reabsorption of phosphate, aa, HCO3,
➡️stimulates 1,25 DH vit D formation
effects of PTH- TERIPARATIDE
elevates serum calcium level
lowers serum phosphate level
TERIPARATIDE form of admin
multiple doses of pre filled pen
moa of TERIPARATIDE
receptor binding increases cAMP
physiologic effect of PTH
bone resorption
pharmacologic effect of PTH: low intermittent dose
bone formation by stimulation of osteoblasts and inc collagen synthesis
inc skeletal mass and bone strength
uses of TERIPARATIDE
postmenopausal osteoporosis
glucocorticoid induced osteoporosis
primary hypogonadism in men
TERIPARATIDE duration of use
2 years only
to prevent risk of osteosarcoma
AE of TERIPARATIDE
nausea vomiting constipation lethargy muscle weakness hypercalcemia hypercalciuria
TERIPARATIDE CI
Paget’s dse of bone
cancer metastasis to bone
open epiphysis- children, young adults
absorption of vit d
intestines
first conversion of vit D by
25 hydroxylase
conversion by 1 hydroxylation
1,25 DH Vit D
conversion by 24 hydroxylation
24,25 DH vit d
storage of vit D
adipose tissue
liver
vit D clearance
liver
moa of vit d
receptor binding @➡️ gene transcription or repression
increase transcription by vit d
vit d receptor gene
calbindin gene
24 hydroxylase enzyme
vit D on the intestine
induction of new protein synthesis
- calcium binding CHON
- intestinal calcium channel
result: enhanced calcium absorption
vit D on bone
stimulates bone resorption - needs PTH
mineralization of newly formed osteoid
induces osteocalcin synth in osteoblasts
marker for osteoblastic bone formation
osteocalcin
vit D on kidney
increase calcium pumps ➡️ decrease calcium excretion
vit D on keratinocytes
calcitriol stimulates differentiation
inhibits proliferation
formation of cornified layer of epidermis ➡️psoriasis
vit D on PTH
decrease levels
vit D on immunity
promote innate immunity
inhibit adaptive immunity
vit D prohormones
cholecalciferol - vit D3
ergocalciferol - vit D2
vit d metabolite
calcitriol- 1,25 DH vit D
vit D analogs
paricalcitol
doxecalciferol
dihyrdrocalciferol
can increase calcium in 24-48 hours
vit d nutritional deficiency
rickets
osteomalacia
defective mineralization in growing bone
rickets