calcium homeostasis :'( Flashcards
name for higher than normal calcium levels
hypercalcemia
3 domains of activity
intake and excretion
storage
control
intake calcium?
calcium absorbed across brush border of intestinal epithelial cells, immediately binds to calbindin (vitamin D dependant protein)
what is calcitriol
active form of vitamin D, regulates calcium intake in intestines
what does calcium intake in the intestines depend on?
adequate vitamin D
calcium excretion?
via bile
what increases renal excretion and inhibits reabsorption
calcitonin - more calcium lost in urine
PTH effects on kidney?
reduces renal excretion (opposite of calcitonin) and processes vitamin D into calcitriol
what gland is calcitonin from
thyroid gland
how is calcium stored
hydroxyapatite in bones (99%)
what does release of calcium depend on
normal bone activity
what directly inhibits osteoclast activity?
calcitonin (from the thyroid gland)
what indirectly stimulates osteoclast activity
RANK-L from osteoblasts
what causes RANK-L to be released from osteoblasts
PTH
where is parathyroid hormone excreted from
parathyroid gland
when is PTH released
when LOW serum Ca is detected
what does PTH act on
kidneys, intestines, osteoblasts
what does the thyroid gland release in response to HIGH calcium
calcitonin
what acts in opposition to PTH
calcitonin
what acts in opposition to calcitonin
PTH
what does calcitonin directly inhibit
osteoclast activity
what two different routes is vitamin D obtained through
absorption of lipid soluble vitamin D in intestines
UVB generation in skin
what happens once vitamin D is synthesised
undergoes two hydroxylations to reach active form
first in liver, second in kidneys
what stimulates hydroxylation of vitamin D in kidneys
PTH and low calcium
vitamin D’s three main actions
stimulating osteoblast to release RANK-L therefore stimulating osteoclasts to increase absorption in GI tract and kidneys
influence of oestrogen?
inhibits bone resorption by inhibiting release of RANK-L from osteoblasts (leads to reduced osteoclast activity therefore less bone resorption)
hypercalcemia response?
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
hypocalcaemia response?
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.
different speeds of pathways for hypocalcaemia?
slow - bone
intermediate - intestinal uptake
fast - renal uptake
