regulation of blood calcium

Question 1

blood calcium is tightly regulated between ___ and ___

Answer 1

8.5 and 10.5

<8.5 = hypocalcemia
>8.5 = hypercalcemia

Question 2

why is blood calcium tightly regulated?

Answer 2

calcium itself is a strong regulatory agent (Ca release & uptake controls skeletal, smooth and cardiac muscle contraction, and neurotransmitters)

Question 3

dietary calcium is absorbed by 2 mechanisms:

Answer 3

1- active transport when diet calcium is low - occurs at beginning of intestine (calcium transport, calcium-binding protein, and calcium ATPase dependent on presence and action of vitamin D –> vitamin D upregulates all these proteins & supercharges mechanism

2- passive transport when diet calcium is high - occurs at end of intestine (vitamin D production is low, calcium absorbed passively thru paracellular pathway)

Question 4

2 hormones involved in regulating blood calcium levels?

Answer 4

PTH & calcitonin

Question 5

parathyroid glands is made in the ___ cells of the ___ glands, it is synthesized and secreted in response to ___

Answer 5

principal/chief cells of parathyroid gland
low blood calcium (blood calcium sensed directly by principal cells by Ca sensing receptor) - normally when Ca is high, Ca sensor keeps parathyroid gene shut off

Question 6

PTH: Ca sensing receptor is a ___ binding protein, but is very sensitive to ___

Answer 6

low affinity Ca binding protein
small changes in calcium concentration (if blood Ca drops by as little as 5%, Ca sensor removes inhibition from PTH gene)

Question 7

PTH targets…

what is its function

Answer 7

bone, kidney, gut
PTH mobilizes calcium from bone to maintain blood levels, also stimulates kidney & intestines to reabsorb more calcium –> brings Ca back up

Question 8

Vitamin D is another regulatory factor in maintaining calcium levels - what is structure?

Answer 8

nonpolar, not very water soluble - has to be carried in blood by Vitamin D binding protein (85% of it carried by this protein)

Question 9

Vitamin D has 2 mechanisms for hormonal action:

Answer 9

1- nonpolar, can dissolve thru membrane to a vitamin D receptor –> migrates to nucleus where binds with retinoid receptor –> activates genes to synthesize all calcium transport proteins to actively transport calcium

2- also acts thru G proteins, phospholipase C, to rapidly insert proteins into membrane

Question 10

calcium deficiency leads to this disease

Answer 10

Rickets, chronic decreased absorption of calcium
long bones grow out

Question 11

calcitonin is ___ to PTH
it is synthesized from ___ of the ___

Answer 11

antagonistic
parafollicular C cells of thyroid

Question 12

calcitonin in synthesized and secreted in response to ____

how does it work?

Answer 12

high blood calcium

inhibits calcium absorption into kidney & intestines, promotes calcium deposition into bone –> lowers Ca levels back down

Question 13

calcitonin is ___ sensitive

Answer 13

estrogen-sensitive

normal action (normal maintenance of bone mass & strength) depends on normal levels of estrogen

osteoporsis downstream result of post-menopausal drop in estrogen