Bone Physiology CIS 9/20 Flashcards
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PTH
secreted when Ca is low in serum. results in stimulation of bone calcium resorption from bone, kidney reabsorption of calcium, decrease in phosphate reabsorption in kidneys, increase in Vitamin D activated
1,25 (OH)2 - Vitamin D
Activated form of vitamin D
- results in gut calcium absorption
- phosphate reabsorption
- kidney tubule calcium reabsorption
- bone calcium reabsorption
hypocalcemia
decreased calcium levels, decreases the sodium voltage threshold, which results in hyperexcitability and spontaneous muscle contraction –> tetany
hypercalcemia
increased calcium levels, results in increased sodium voltage threshold, causing NS depression and slow reflex responses
osteon
structural unit of the bone
lacunae
irregular plates on trabecular bone where bone resportption has occured (contain osteocytes)
lamellar bone
layers of organized bone
osteoid
organic matrix of bone (laid down by osteoblasts)
increased bone formation due to which hormones….
growth hormone, thyroid, insulin, gonadal hormones
glucocorticoids
suppress calcium gut absorption by depleting osteoblasts –> suppresses bone formation
Plekho 1
Pleckho1 is responsible for degradation of cofactors for osteoblastic activity. inhibition of Pleckho1 will result in increased bone density. Findings support increased bone density in a mouse model with Pleckho1 siRNA treatment. A novel finding in this article was the uncoupling of bone resorption and bone formation.
Sclerostin
The normal function of sclerostin is a reduction in osteoblast activity. By inhibiting sclerostin action (blocking antibody) bone formation can potentially be increased.
T score
low T score is indicative of osteoporosis (less than -2.5)
urine N-telopeptide
- marker of collagen degredation
- result of increased osteoporosis
alkaline phosphatase
- linked with bond formation
- seen high in children and in those with Paget’s disease
How do osteoblasts work along with osteoclasts?
- Low Calcium levels results in release of PTH. PTH activates osteblasts which secrete MCSF and RankL/IL6. MCSF recruits osteoclasts. Osteoclasts are activated by RankL?IL-6 and the reabsorption of bone by osteoclasts , which is followed by the osteoblasts laying down new bone. This results in an increase in plasma calcium levels
- decreased RankL is seen in osteopetrosis
- increased RankL is seen in osteoporosis
secondary causes of osteoporosis
- vitamin D deficiency
- increased PTH
- renal failure
- glucocorticoid excess
- hypogonadism
- increased thyroid hormone
- idiopathic hypercalcemia
OPG
inhibits RankL/IL6 - and stops osteoclast action
FGF23
- phosphate regulation at kidney level
- increase in FGF23 results in decreased Vitamin D and decreased Phosphate levels
bisphosphates
- inhibit bone resorption – could lead to hypocalcemia, but is used to treat osteoporosis
- Prolia drug has a similar affect, but instead inhibits the binding of RankL/Rank and IL6R/IL6
Osteoporosis
decreased bone density
Osteomalacia/Rickets
disordered bone mineralization (due to decrease in vitamin D) –> decreased bone density/brittle bones
Paget’s Disease
hyperactive bone remodelling by osteoblasts
Osteogenesis Imperfecta (OI)
brittle bone disease: due to mutations in collagen
- Type I: decreased amount of collage, with normal structure due to inherited missing allele
- Type II: (most severe) - due to a point mutation in colagen resulting in abnormal collagen structure
osteopetrosis
defective osteoclasts, results in increased bone density and disorganized bone structure
