Acid Base Balance

Question 1

consider exogenous/endogenous acid sources, outline how alterations of acid levels occur

Answer 1

exogenous: dietary intake (meat>veg acids)
endo: metabolic byproducts:
- volatile acids (H2CO3)
- non-volatile (H2SO4, H3PO4)
- organic

kidneys accomplish pH maintenance by:

1. reabsorption filtered HCo3- in PT
2. pair generation of NEW HCO3- with secretion of H+ as H2PO4- or NH4+

Question 2

describe pathways for HCO3- reclamation/generation in PT, explain how these act to accommodate increased acid load

Answer 2

NHE3 uses Na+ gradient (from Na/K ATPase) to move H+ out of lumen
CAIV (carbonic anhydrase) catalyzes conversion HCO3- and H+ to CO2 and H2O
tubular CO2/H2O enter cell. CAII converts to HCo3 and H+
HCO3- leaves via basolateral NBC1 and is reclaimed

= H+ recycled and filtered HCO3- reclaimed (no net gain)

Question 3

compare/contrast compensation mechanisms for acid-base disturbances

Answer 3

excretion ammonium most effective for increased acid load

log ratio [HCO3-]/PCO2 = 20:1, then pH will remain 7.4

Question 4

generation NEW HCO3-

Answer 4

PT:
CAII catalyzes production HCO3- and H+
NHE3 uses Na+ gradient to move H+ to lumen
secreted H+ titrates luminal HPO42- to form H2PO4-
newly generated HCO3- leaves via basolateral NBC1 and added to stores

NET: H+ excreted as H2PO4-, HCO3- generated

OR 2 H+ can be secreted as NH4+, and 2 HCO3- generated (more effective to get rid of acid/buffer quickly)

Question 5

metabolic vs respiratory disturbance

Answer 5

metabolic (i.e. change HCO3-) = respiratory compensation. if not enough HCO3- (acidosis), compensate by decrease PCO2. if too much HCo3, increase PCO2

respiratory= metabolic compensation. if too much PCO2 (acidosis), then increase HCO3-