26. Renal Control of Acid/Base Balance Flashcards
What range does blood pH need to remain in?
7.35-7.45
What processes increase the amount of acid in blood?
- Metabolism produces CO2
- Breakdown of food produces non-volatile acids
- Metabolic intermediates (eg. lactic acid)
What are the 4 buffering systems in the body?
Bicarbonate
Phosphate
Haemoglobin
Plasma and cell proteins
What organs maintain blood pH?
Lungs (blow off CO2)
Kidneys (Control HCO3-)
What does blood pH depend on?
Ratio of HCO3- to H2CO3-
In practice, pCO2 is used for H2CO3
What concentration of HCO3- do the kidneys maintain?
24mmol/L
What pCO2 is maintained at by the lungs?
40mmHg
What concentration is H2CO3 maintained at?
1.2mmol/L
What is the Henderson-Hasselbach equation?
pKa+ log (base/acid)
What ratio of HCO3-/H2CO3 is needed to maintain a pH of 7.4?
20:1
What compensation occurs when acid is added to the blood?
- Bicarbonate is used up as a buffer
H2CO3 is broken to CO@ and H2O - CO2 can be blown off by the lungs
- Kidneys add new HCO3- to the blood and secrete H+
How do the kidneys control pH balance?
Reabsorb filtered bicarb
Make new bicarbonate (equal to amount used up by buffering)
Tubular secretion of H+
How is HCO3- reabsorbed?
H2CO3 converted to water and CO2 in the filtrate
These recombine in the tubular cell to produce H+ and HCO3-
HCO3- crosses basolateral membrane and H+ is secreted
How is bicarbonate made in the tubular cell?
CO2 from blood combined with OH- from water
Remaining H+ is buffered by HPO4^2-
What transporters are used to secrete H+?
ATP-driven H+ pump in CD
Na/H exchanger in PCT, DT, CD
H/K exchanger
What buffers titratable acid in urine?
Phosphate in PCT
Creatinine in DCT
What is the main site of NH3 synthesis?
PCT cells
What is needed for the reaction that converts glutamine to NH3 and glutamate?
Glutaminase
What are the advantages of the kidneys producing its own buffer?
Ensures plentiful supply
Can make more if there is increased acid
Glutaminase is stimulated by acidosis
