Calcium metabolism and homeostasis

Question 1

how much calcium is in the body?

Answer 1

1-1.4 kg

Question 2

what Is the distribution of calcium in the body?

Answer 2

bone - 99%
extracellular - Ionised Ca 1.2mmol/L
intracellular - cytosolic 10-4 - 10-3 mmol/L

Question 3

what are the biological roles of calcium?

Answer 3

-mineralisation of bones and teeth
Ca5(PO4)3OH (hydroxyapatite)
-calcium ions in intracellular and extracellular fluid are essential to many biochemical processes

Question 4

which biochemical processes are calcium ions involved in?

Answer 4

-neuromuscular excitability and maintenance of membrane potential
-blood clotting cascade
-hormonal secretion
-enzymatic regulation
-cell signalling

Question 5

what is calciums role in heart muscle excitation?

Answer 5

depolarisation produced by action potential opens calcium channels in surface membrane and transverse tubules in cardiomyocytes

Question 6

what does calcium release from sarcoplasmic reticulum result in?

Answer 6

-calcium binds to troponin
-sliding of thick filament and thin filaments
-cell shortening
-development of pressure within the ventricle and ejection of blood

Question 7

of the 1% of calcium not in the bone, where is it found?

Answer 7

50% - non bound called as ionised or free dialysable
10% - bound to anions PO4,HCO3,SO4, citrate
40% - blood calcium, protein bound, (albumin =70% to 80%)

Question 8

what is tested for in a bone profile?

Answer 8

calcium
adjusted calcium
phosphate
albumin
alkaline phosphate

Question 9

what is the composition of calcium in plasma?

Answer 9

free (unbound/ionised) -47%
bound to albumin -47%
complexed -6%

Question 10

how do we measure albumin?

Answer 10

feedback mechanisms are regulated by the free fraction - physiologically important- although were not very good at measuring it
measure total calcium
=free+bound+complexed

Question 11

what happens if a patient has a low albumin conc?

Answer 11

the total calcium will also be low but the free calcium might be quite normal

Question 12

what is calciums role in metabolic control?

Answer 12

parathyroid hormone (PTH)
1,25 dihydroxyvitamin D (1,25DHCC)

Question 13

what organs are involved in the metabolic control of calcium?

Answer 13

parathyroid glands
-calcium sensing receptors
-kidney
-gut
-bone

Question 14

how do calcium sensing receptors work?

Answer 14

on parathyroid cells - minute to minute responses to ionised Ca
main physciologicsala ligand is Ca
serves as a calciostat for calcium homeostasis

Question 15

how does parathyroid hormone work?

Answer 15

-a 84 amino acid polypeptide produced by the parathyroid glands
-secretion is regulated by free/ ionised calcium, sensed by the calcium sensing receptors
-measurment is by immunoassay

Question 16

how much vitamin D do we generally get from sunlight?

Answer 16

80%

Question 17

what is the process of vitamin D metabolism?

Answer 17

cholecalciferol
25(OH)cholecalciferol
1,25(OH)2 cholecalciferol

Question 18

where does cholecalciferol change to 25(OH)cholecalciferol?

Answer 18

in the liver

Question 19

where does 25(OH)cholecalciferol change into1,25(OH)2 cholecalciferol?

Answer 19

in the kidney

Question 20

what happens in response to a decrease in ionised Ca, PTH?

Answer 20

-stimulates calcium resorption in renal tubule
-stimulates formation of 1,25 DHCC in kidney which enhances calcium absorption from gut and bone resorption
-promotes bone resorption