Blood Buffer pH equation…
pH = 6.1 + log [bicarb] / (0.03 x PCO2)
A 1 unit change in pH indicates a ___-fold increase in hydrogen ion concentration
10x
13,000 - 20,000 mEq/day of volatile acid is handled by ______ and excreted as_____
lungs as CO2
Non-volatile, or fixed, acids are handled by…
the kidney
What is responsible for 75% of fixed acid production?
methionine and cysteine catabolism forming sulfuric acid
What are the primary intracellular buffers?
proteins
Phosphate
Mass action rule notes that for every ________ increase in PCO2, bicarb will increase by _______
10 mmHg PCO2 increase
1 mEq/L bicarb increase
Mass action rule notes that for every ________ decrease in PCO2, bicarb will decrease by _______
10 mmHg PCO2 decrease
2 mEq/L bicarb decrease
What regulates respiration?
plasma PCO2
By what 3 mechanisms do the kidneys keep bicarb steady between 22-26?
complete recovery of filtered bicarb when over 26
synthesis above GFR
Excretion when excess
What drives bicarb recovery in the nephron?
secretion of hydrogen ions
In the PT, H+ is __________ and in the DT H+ is ________
H+ - sodium exchange (NHE) in PT
Active secretion in DT
Bicarbonate is most absorbed in the _____ (x%), then the _____ (x%), and then the _____ (x%)
PT (85%)
Ascending thick limb (10%)
Collecting duct (5%)
What percent of filtered bicarb is reabsorbed?
99.9%
What two hormones, when acting on the PT, increase bicarb reabsorption?
AT II
Aldosterone
This hormone, when active in the PT:
increases expression of sodium-hydrogen exchanger, which pumps hydrogen from ICF to lumen, allowing Bicarb to be transported to the ECF via sodium cotransport
AT II
This hormone, when active in the PT:
increases expression of H+ ATPase, which pumps hydrogen from ICF to lumen, allowing Bicarb to be transported to the ECF via sodium cotransport
Aldosterone
What enzyme catalyzes the reaction of water and carbon dioxide to form hydrogen ions and bicarb?
carbonic anhydrase
This hormone, when active in the alpha-intercalated cells of the CD:
Increases expression of the H+-ATPase which pumps hydrogen from ICF to lumen, allowing Bicarb to be transported to the ECF via chloride cotransport
aldosterone
hydrogen ions leave the PT tubule cells by what two mechanisms?
Sodium - Hydrogen Exchanger
H+-ATPase
Hydrogen ions leave the alpha intercalated cells of the CD by what two mechanisms?
H+-ATPase
H+-Potassium Exchanger
Bicarb leaves the alpha intercalated distal tubule cell for reabsorption via what mechanism?
bicarb-chloride exchanger
Bicarb leaves the tubule cell of the PT via what two mechanisms?
Sodium-Bicarb cotransport
Bicarb-chloride exchange
for every bicarb neutralized in the tubule, ___ bicarb(s) is/are released into the PTC…
1
luminal pH may drop as low as ____ once bicarb is absent from filtrate
4.5
How is the kidney able to release more bicarb to the PTC than is present in the filtrate?
phosphate and NH3 accept H+ in the tubule to allow secretion of H+, and release of bicarb to PTC
Describe the mechanism by which bicarbonate can be produced in the distal nephron…
H20 + CO2 –> Carbonic acid
(catalyzed by carbonic anhydrase)
In order for carbonic acid to enter the tubule, there must be a non-bicarb buffer (PO4, NH3)
H+ crosses apical border to tubule, binds with NH4+ or PO4, and bicarb free to enter PTC
In the PT, Glutamine becomes ____ and _____ via glutaminase.
NH4+ splits to NH3 and hydrogen, they both diffuses to the lumen (together/separate?), where they are rejoined as NH4+
AKG is converted to ______, and is cotransported to the PTC with ______
AKG and NH4+
NH3 and H+ diffuse to lumen separately
AKG converted to bicarb
Cotransported with sodium
1 glutamine will yield ___ bicarbs and ____ NH4+s
2
What regulates synthesis of NH4+ from glutamine?
pH
acidosis _____ glutamine catabolism…
increases
What is the primary mechanism for dealing with chronic acid loads?
synthesis of NH4+ from glutamine