Calcium Homeostasis in Children

00:02 In this lecture we will review calcium homeostasis disorders such as hypocalcemia and hypercalcemia.

00:10 So in order to think about this let's try and remember the basic fundamental control mechanism of our calcium levels in our blood.

00:20 Parathyroid hormone is controlling this and the parathyroid hormone receptor.

00:25 We have vitamin D controlling this and we have a calcium-sensing receptor and these are all things that are helping us to control our levels.

00:34 On this slide you can see a general overview of how we control calcium levels.

00:39 Let's go through this bit by bit.

00:41 Remember vitamin D in general is absorb from the skin through light exposure or in the diets.

00:49 In patients with darker skin there is less effective absorption of light and conversion of vitamin D in our blood.

00:58 Generally, this vitamin D level is then travels to the liver where this metabolize into 25-hydroxy vitamin D.

01:07 It then goes from the liver to the kidney and the kidney turns this in to 1,25-Dihydroxy vitamin D which is the active metabolite of vitamin D.

01:18 The kidney can dispose of 1,25-hydroxy vitamin D.

01:24 So it's a bit difficult to overdose on that particular formulation.

01:28 The 1,25-hydroxy vitamin D then goes to the bone where it promotes the resorption of calcium and phosphate from the bone and into the blood.

01:39 Likewise, the 1,25-hydroxy vitamin D, proceeds to the intestine where it promotes absorption of calcium and phosphate from ingested contents.

01:52 Also, remember that PTH has an effect of increasing 1,25-hydroxy vitamin D conversion in the kidney and promotes resorption via the osteoclast.

02:07 And remember there is a negative feedback loop where 1,25-hydroxy vitamin D is actually inhibiting the activity of parathyroid hormone.

02:18 Basically all of these activities promote the production of calcium and phosphorus in the blood and those two metabolites go on to be important in both bone mineralization, a variety of metabolic functions and neuromuscular functions, especially the calcium.

02:38 There are a few things that can inhibit calcium in the blood outside of the system, one is high phosphate levels.

02:46 High phosphate levels reduce serum calcium through simple binding of the two elements together and deposition in tissues.

02:54 Likewise, a low magnesium will inhibit the production of calcium because magnesium is a cofactor for the function of the parathyroid hormone.

03:04 So ionized calcium can be measured, probably we should stop getting calcium levels because that will go up and down depending on binding to albumin.

03:16 But ionized calcium can be measured and this is the true amount of calcium in the blood.

03:21 Total calcium needs to be corrected if there is low albumin, because some albumin is binding some of that calcium and thus the calcium levels maybe off.

03:32 In fact we're going to adjust that using a formula.

03:35 For every gram that your albumin is low you should actually correct your calcium up by 0.8.