Calcium reabsorption from egg shell during embryogenesis, how is carbonate neutralized?
As the embryo reabsorbs calcium from the shell, it also reabsorbs an equal quantity of carbonate. Calcium is in quite high concentrations in the body, the same molarity for carbonate causes a very alkaline environment. Carbonate has a pKa near 10, seen in that the egg white in "food eggs" (non-incubated and non-impregnated) becomes alkaline as the egg ages, approaching pH 9 to 10.
Throwing some numbers in there, assuming 2.2 gram of CaCO3, 8% reabsorbed to cause the average 8% thinning documented here (this is also just day 3-5 I think. ) 2.2 gram*8% = 0.176 gram carbonate released. The molecular weight of carbonate is 61 g/mol, 0.176 g / 61 g/mol = 0.003 mol = 3 mmol. If newborn chicken weighs 85 gram, and is 70% fluid, 85 gram * 70% = 60 gram. 60 gram is 0.06 L water. 3 mmol carbonate equivalent to 3 mmol/0.06 L = 50 mmol/L. The solution gets a pH of 11, and if you add 25 mmol/L of hydrochloric acid it is still at pH 9.2.
How is that carbonate neutralized?
At least 1 carbonate ion in 5 can be neutralized by bone formation, since hydroxyapatite has a ratio of 5:1 calcium to hydroxide ions, and, 99% of calcium is in bone (assuming somewhat similar ratio in infant as well. 979
) What about the other 4?
EDIT: A user <PERSON> emphasizes that Wikipedia's entry on Calcium carbonate gives a pKa of 9. I based pKa closer to 10 on equilibrium between carbonate and bicarbonate. 9 or 10 does not really change the question that much since its about the huge quantity of base, quite strong in either case. I used http://www.aqion.onl/ for pH calculations giving pH 11. Feel free to use the correct value.
EDIT: Carbonic acid from CO2 from cellular respiration was mentioned. Carbonic acid from cellular respiration is at least part of it. But I don't know if it is all of it or close to all of it. 3 mmol of calcium absorbed (see <PERSON>, 1973) if average egg volume is 50 mL, molarity is 60 mmol/L, and this is as carbonate which saturates pCO2/H2CO3/HCO3-/CO3^2- as well.
EDIT: Also quite a lot of uric acid created, 2.3 gram per L by day 13, jbc.org/content/70/2/535.full.pdf, molarity 14 mmol/L.
SUMMARY: Bone formation likely takes care of 1 in 5 carbonates. Carbonic acid from cellular respiration, uric acid from nitrogen excretion, both contribute. Other factors? 979