Lec 6 - Calcium Flashcards
how much NET intake of ca a day
200mg
how much ca stored in bone
about 1kg
how much ca excreted in kidneys
200mg
balance in whats absorbed and whays secreted
what is 40% of ca in body bound to
macromolecular proteins e.g. albumin
how much Ca complexed as Ca2+ salts in body
5%
how much free ionised Ca conc in body
1.2mM
3 calcitropic hormones
- parathyroid horomone
- vit D
- calcitonin
where is parathyroid (pth) released from
chief cells in parathyroid gland
relationship of PTH and Ca levels
inversly proportional
- low Ca = high PTH secretion
vice versa
(VERY tightly controlled, 1.1 or 1.3 not good enough)
what do parathyroid cells have to detect ca levels
CaR
calcium sensing receptor
GPCR
where else is CaR present
in kidney
to limit Ca reabsorption
3 ways that pth increases Ca levels
- increases bone resorption
- increased renal ca2+ reabsorption
- increased vit D production
how does bone turnover work
- chronically elevated PTH levels = mineralised bone resorption into demineralised bone
- which releases Ca2+ into plasma
- if PULSATILE pth release, increases bone formation
% ca reabsorbed in proximal tubule
~70%
a lot cuz most stuff is reabsorbed
% ca reabsorbed in thick ascending limb
~20%
lots of CaR here, PTH acts here
% ca reabsorbed in distal convultued tubule
~9%
because after this point only 1% is left to excrete= little changes can lead to big difference in whether Ca excreted
- PTH acts here too
vit D production
provitamin D3 =
(via UVB)
previtamin D3=
vit D3=
25(OH)D3 (in liver)=
1,25(OH)2D3 (in kidney)
which enzyme needed to make mature vit D
1 alpha OHase
(PTH increases its expression)
what does vit D do that PTH cant
can do everything PTH does
AND
increases net intestinal Ca uptake
how do we ensure free Ca levels dont go up too much in cell
calcium binding proteins
(CALBINDINS)
(otherwsie too much Ca is a death signal for a cell)
name of claium selective channels in duodenum cells
TRPV5
TRPV6
2 proteins needed to get Ca out of cell
plasma membrane calcium ATPase (PMCA)
and
sodium calcium exchanger (NCX)
where else does calbindin act other than the gut
kidney
as calbindin D28K
(same principle as gut)
only difference in gut and kidney absorption of vit D
in gut theres more TRPV6
in kidney theres more TRPV5
