hco3 reabsorption

okey, i've been reading the acid base regulation of kidney for a few times. i got it when i was readng it, but i cant really summarise them in my mind when i tried to. they just didnt flow well.

so i tot i'll try to write down what i knew about them.

here is i think one of the most important fact about hco3 reabsorption.
hco3 is impermeable at the membrane, so they cant cross the membrane by themselves.
sooo, they coombine with H+ to become h2co3 which then will dissociate to become water and co2.
co2 is the one who can cross the membrane into the tubular cells.
in the cells, co2 will combine with water.catalysed by carbonic anhydrase and become h2co3.
h2co3 will dissociate into H+ and hco3.
then only hco3 can get into the interstitial and then blood.
hco3 transport into the interstitial is coupled with cl-(exchange) and na+(cotransport).

so it's like for every h+ secreted into the tubule, one hco3 will appear in the cells.
for the h+ secretions, they r a bit different in the proximal tubule and distal tubules.

in proximal tubules, h+ is secreted by secondary active transport. coupled with na+ reabsorption. na+ moves down concentration gradient. so the energy released is used to take h+ out of the cells into the tubule.
but start from late distal tubules, h+ is secreted by primary active transport. in a specialised cells - intercalated cells. h+ is transported by hydrogen ATPase. that means the energy is from the breakdown of ATP.

okey, that's only the reabsorption part. that's the most handle-able ones.

p/s : yeeey..i've become a nerd as i wished for,bcos who else will post this stuff into their blog if for they arent nerdy2 ??