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PMCOL 200 > Bone Minerals > Flashcards

Bone Minerals Flashcards

1
Q

what are the 2 main ions in bone mineral homeostasis?

A

Ca^2+ (mainly) and PO4^3-

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2
Q

where is the principal reservoir for Ca and phosphate?

A

bone (then ICF and circ)

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3
Q

why is regulation of Ca and PO4 important?

A

health/strength of bones (long-term), electrical excitability (acute), intracellular signalling for gene expression

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4
Q

what is osteoporosis, osteopenia, and osteopetrosis?

A

osteoporosis: severe bone density loss (breakable)
osteopenia: decr bone density/softening
osteopetrosis: incr bone density/hardening (breakable)

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5
Q

what are 3 control sites (input/exhaust pathways) for Ca and PO4 plasma levels?

A

Gut, bone, kidneys

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6
Q

what 2 hormones control Ca and PO4 levels in body?

A

vitamin D3 and PTH

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7
Q

what is the function of osteoblasts vs osteoclasts?

A

blasts: bone deposition
clasts: resorption

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8
Q

how do vit D and PTH regulate bone resorption?

A

hormones activate osteoblasts which secrete RANK ligand (RANKL) and activate osteoclasts (indirect activation)

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9
Q

what is the effect of PTH in bones and kidneys (Ca and PO4 levels)? net?

A

bones: incr resorption, incr Ca and PO4 levels
kidneys: incr Ca reabsorption and PO4 excretion, incr Ca and decr PO4 (+ stimulates vit D met.)
NET: incr Ca, decr or maintain PO4

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10
Q

what triggers incr PTH secretion from PTG?

A

decr Ca levels

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11
Q

what is vitamin D?

A

“steroid” hormone (secosteroid, steroid - 1 ring)

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12
Q

what is the metabolization process of vit D3?

A

(from diet or sunlight) liver metabolizes vit D3 to 25-OH-D3, kidney metabolizes into active calcitriol (1,25-hydroxy vit D3) or inactive secalciferol (24,25-hydroxy D3)

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13
Q

what is the effect of vit D3 in bones, kidneys, and gut (Ca and PO4 levels)? net?

A

bones: incr resorption, incr Ca and PO4
kidneys: decr Ca and PO4 excretion, incr Ca and PO4
gut: incr Ca and PO4 absorption, incr Ca and PO4
NET: incr Ca and PO4

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14
Q

what triggers vit D3 conversion to calcitriol (1,25-hydroxy vit D3) vs secalciferol (24,25-hydroxy D3)?

A

calcitriol: low Ca/high PTH
secalciferol: high Ca/calcitriol (1,25-OH D3)

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15
Q

what senses plasma Ca levels?

A

Ca receptors in PTG

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16
Q

where are PTH receptors found?

A

kidney and osteoblasts (bone)

17
Q

how does PTH affect vit D and thus Ca and PO4 levels?

A

PTH incr vit D conversion to 1,25 form (active) which incr Ca and PO4 levels (gut, kidneys, and bone)

18
Q

what are 3 symptoms and 2 treatments for acute hypocalcemia?

A

symptom: hyperexcitability, Trousseau’s sign (arm muscle contraction w/ BP cuff), seizures/spasms
treatment: Ca or active vit D3 supplement

19
Q

what is the long-term danger of hypocalcemia?

A

can develop 2ndary hyperparathyroidism (decr Ca causes constant PTH secretion), consistent breakdown/weakening of bone

20
Q

what are 2 underlying defects of hypocalcemia?

A

hypoparathyroidism (fix: Ca/vitD suppl) or vitamin D deficiency (fix: diet, suppl, sunshine)

21
Q

what are 3 symptoms and 4 treatments for acute hypercalcemia?

A

symptoms: hypoexcitability, lethargy, bone pain if high PTH (can go into coma)
treatments: resect PTG, vit D supplements, therapeutics to protect bone, calcimimetics

22
Q

what is a possible underlying defect of hypocalcemia?

A

primary hyperparathyroidism (tumor?)

23
Q

what is osteoporosis?

A

abnormal bone loss that can lead to fractures (slow onset, long-term) - bone is porous

24
Q

t/f: osteoporosis in common in ageing females

A

true, b/c decr estrogen

25
Q

what is a possible treatment for osteoporosis in ageing females?

A

hormone replacement or estrogen mimetics

26
Q

what are 2 other causes for osteoporosis? (not female ageing)

A

long-term glucocorticoid administration, hyperparathyroidism

27
Q

what is teriparatide?

A

recombinant, fully active PTH fragment (1-34)

28
Q

how does teriparatide (PTH fragment) treat osteoporosis if PTH incr bone resorption?

A

given in a pulsatile manner to stimulate bone deposition by osteoblasts (have PTH Rs) wo/ stimulating osteoclasts indirectly via RANKL

29
Q

what are bisphosphonates?

A

inhibitors of osteoclast resorption of bone (cause apoptosis)

30
Q

what are 3 possible side effects of bisphosphonates?

A

cancer, fractures, GC inhibition

31
Q

what is the general structure of bisphosphonates?

A

two phosphonate groups (pyrophosphate)

32
Q

what is the most commonly prescribed bisphosphonate?

A

alendronate

33
Q

what allows bisphosphonates to accumulate in bone?

A

PO4- groups have a high affinity for Ca2+ (can target osteoclasts)

34
Q

what is osteoprotenerin?

A

endogenous RANKL inhibitor (binds to RANKL)

35
Q

what is the effect of osteoprotegerin?

A

prevents RANKL from binding and activating osteoclasts, which decr bone resorption

36
Q

what is denosumab?

A

monoclonal Ab that inhibits RANKL (~osteoprotegerin)

PMCOL 200 (27 decks)

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