Lec 6 - Calcium

Question 1

how much NET intake of ca a day

Answer 1

200mg

Question 2

how much ca stored in bone

Answer 2

about 1kg

Question 3

how much ca excreted in kidneys

Answer 3

200mg
balance in whats absorbed and whays secreted

Question 4

what is 40% of ca in body bound to

Answer 4

macromolecular proteins e.g. albumin

Question 5

how much Ca complexed as Ca2+ salts in body

Answer 5

5%

Question 6

how much free ionised Ca conc in body

Answer 6

1.2mM

Question 7

3 calcitropic hormones

Answer 7

• parathyroid horomone
• vit D
• calcitonin

Question 8

where is parathyroid (pth) released from

Answer 8

chief cells in parathyroid gland

Question 9

relationship of PTH and Ca levels

Answer 9

inversly proportional
- low Ca = high PTH secretion
vice versa
(VERY tightly controlled, 1.1 or 1.3 not good enough)

Question 10

what do parathyroid cells have to detect ca levels

Answer 10

CaR
calcium sensing receptor
GPCR

Question 11

where else is CaR present

Answer 11

in kidney
to limit Ca reabsorption

Question 12

3 ways that pth increases Ca levels

Answer 12

• increases bone resorption
• increased renal ca2+ reabsorption
• increased vit D production

Question 13

how does bone turnover work

Answer 13

• chronically elevated PTH levels = mineralised bone resorption into demineralised bone
• which releases Ca2+ into plasma
• if PULSATILE pth release, increases bone formation

Question 14

% ca reabsorbed in proximal tubule

Answer 14

~70%
a lot cuz most stuff is reabsorbed

Question 15

% ca reabsorbed in thick ascending limb

Answer 15

~20%
lots of CaR here, PTH acts here

Question 16

% ca reabsorbed in distal convultued tubule

Answer 16

~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

Question 17

vit D production

Answer 17

provitamin D3 =
(via UVB)
previtamin D3=
vit D3=
25(OH)D3 (in liver)=
1,25(OH)2D3 (in kidney)

Question 18

which enzyme needed to make mature vit D

Answer 18

1 alpha OHase
(PTH increases its expression)

Question 19

what does vit D do that PTH cant

Answer 19

can do everything PTH does
AND
increases net intestinal Ca uptake

Question 20

how do we ensure free Ca levels dont go up too much in cell

Answer 20

calcium binding proteins
(CALBINDINS)
(otherwsie too much Ca is a death signal for a cell)

Question 21

name of claium selective channels in duodenum cells

Answer 21

TRPV5
TRPV6

Question 22

2 proteins needed to get Ca out of cell

Answer 22

plasma membrane calcium ATPase (PMCA)
and
sodium calcium exchanger (NCX)

Question 23

where else does calbindin act other than the gut

Answer 23

kidney
as calbindin D28K
(same principle as gut)

Question 24

only difference in gut and kidney absorption of vit D

Answer 24

in gut theres more TRPV6
in kidney theres more TRPV5

Question 25

where is calcitonin released from

Answer 25

parafollucular thyroid cells

Question 26

half life of calcitonin

Answer 26

5 mins
vry short

Question 27

name cells that degrade bone

Answer 27

osteoclasts

Question 28

what does claclitonin do

Answer 28

decreases Ca2+ in plasma
- by decreasing osteoclast activity
- so increasing bone deposition

Question 29

what is calcitonin inhibited by

Answer 29

low levels of ca in blood

Question 30

calcitonin in fish

Answer 30

plays larger role
more important to keep Ca down
high threat of hypercalcaemia

Question 31

what is primary hyperthyroidism

Answer 31

overactive parathyroid gland
too much PTH
too much Ca

Question 32

rickets

Answer 32

• vit D deficiency due to mutatiion in 1 alpha OHase