calcium homeostasis :'( Flashcards

1
Q

name for higher than normal calcium levels

A

hypercalcemia

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2
Q

3 domains of activity

A

intake and excretion
storage
control

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3
Q

intake calcium?

A

calcium absorbed across brush border of intestinal epithelial cells, immediately binds to calbindin (vitamin D dependant protein)

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4
Q

what is calcitriol

A

active form of vitamin D, regulates calcium intake in intestines

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5
Q

what does calcium intake in the intestines depend on?

A

adequate vitamin D

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6
Q

calcium excretion?

A

via bile

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7
Q

what increases renal excretion and inhibits reabsorption

A

calcitonin - more calcium lost in urine

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8
Q

PTH effects on kidney?

A

reduces renal excretion (opposite of calcitonin) and processes vitamin D into calcitriol

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9
Q

what gland is calcitonin from

A

thyroid gland

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10
Q

how is calcium stored

A

hydroxyapatite in bones (99%)

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11
Q

what does release of calcium depend on

A

normal bone activity

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12
Q

what directly inhibits osteoclast activity?

A

calcitonin (from the thyroid gland)

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13
Q

what indirectly stimulates osteoclast activity

A

RANK-L from osteoblasts

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14
Q

what causes RANK-L to be released from osteoblasts

A

PTH

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15
Q

where is parathyroid hormone excreted from

A

parathyroid gland

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16
Q

when is PTH released

A

when LOW serum Ca is detected

17
Q

what does PTH act on

A

kidneys, intestines, osteoblasts

18
Q

what does the thyroid gland release in response to HIGH calcium

A

calcitonin

19
Q

what acts in opposition to PTH

A

calcitonin

20
Q

what acts in opposition to calcitonin

A

PTH

21
Q

what does calcitonin directly inhibit

A

osteoclast activity

22
Q

what two different routes is vitamin D obtained through

A

absorption of lipid soluble vitamin D in intestines
UVB generation in skin

23
Q

what happens once vitamin D is synthesised

A

undergoes two hydroxylations to reach active form
first in liver, second in kidneys

24
Q

what stimulates hydroxylation of vitamin D in kidneys

A

PTH and low calcium

25
Q

vitamin D’s three main actions

A

stimulating osteoblast to release RANK-L therefore stimulating osteoclasts to increase absorption in GI tract and kidneys

26
Q

influence of oestrogen?

A

inhibits bone resorption by inhibiting release of RANK-L from osteoblasts (leads to reduced osteoclast activity therefore less bone resorption)

27
Q

hypercalcemia response?

A

detected by thyroid which releases CALCITONIN which acts on kidneys to reduce renal uptake of calcium therefore more is lost in urine. calcitonin also inhibits osteoclast activity so less calcium is released into circulation from bone

28
Q

hypocalcaemia response?

A

parathyroid gland releases PTH. stimulates osteoblasts increasing release of RANK-L, IL/MCSF. this stimulates osteoclast differentiation and activity, and the reabsorb bone.

PTH also stimulates hydroxylation of vitamin D into active form CALCITRIOL. PTH and calcitriol increase RANK-L released from osteoblasts, increase calcium uptake in kidneys and intestine.

29
Q

different speeds of pathways for hypocalcaemia?

A

slow - bone
intermediate - intestinal uptake
fast - renal uptake