Acid-base imbalance - questions (Q1)

Here are some answer guides. They are merely guides. You can read up own your own.
Prof Faridah

Q1. Alkalosis causes decrease in free calcium ions due to association with protein. But in milk-alkali syndrome, the alkaemia will cause an increase in renal absorption of calcium --> hypercalcemia...so..?

a) Is it alkalosis will cause decrease in calcium, provided only if the kidney is dysfunctional? So there is no reabsorption?

b) Does alkaemia and alkalosis have different effects on the calcium ions? If yes, how? Examples?

My response:

1.  Calcium ion binding (association) and dissociation from albumin are reversible processes, and are dependent on blood pH. Acidosis favours calcium ion dissociation, while alkalosis favours calcium ion binding.
2. Calcium levels in blood are determined in the clinical lab 2 ways, as Total calcium and as Ionised calcium. Total calcium is the sum of free Ionised calcium + Protein-bound calcium. Total calcium is a cheaper test to do than Ionised calcium. For most clinical labs, Total calcium will suffice. Rarely is Ionised calcium requested by doctors.
3. Hypercalcemia prevails in alkalosis. This hypercalcemia is marked by high Total calcium levels but low Ionised calcium levels. This is because alkalosis itself favours binding of free Ionised calcium (Ca2+) to proteins, and the most abundant plasma protein is albumin. So, alkalosis favours binding of calcium ions to albumin, thus reducing the value for free Ionised calcium; Total calcium remains high.
4. Previously, people were taking "milk of magnesia" as a remedy for dyspepsia (any stomach upset). Milk of magnesia is an alkaline preparation and an OTC substance (over the counter; means can be purchased without prescription). Of course people may have taken it in excess and for extended periods as usually stomach complaints don't usually go away that easily.
5. When alkaline media is taken in large amounts and for extended periods, it can result in milk-alkali syndrome. If left untreated, milk-alkali syndrome may lead to metastatic calcification and renal failure. The kidneys is dysfunctional in renal failure. Since this condition is alkalosis, and the renal system is dysfunctional, excess bicarbonate and calcium are not excreted or are minimally excreted, if any. Thus, in milk-alkali syndrome with renal failure, we should see a severe alkalosis with hypercalcemia.
6. Alkalosis refers to alkaline conditions within cells; alkalaemia refers to alkaline conditions within blood; both have pH>7 (by chemical definiton) (>pH7.4 by physiological definition).