Renal Regulation of [H+]

Question 0

Bicarbonate Conservation

Answer 0

HCO3- + H+ => H20 + CO2
*CA on the lumina membrane catalyzes this rxn

• CO2 and H20 passively diffuses into the tubular cell where the reverse rxn occurs
• HCO3- is reabsorbed via HCO3-/Cl- cotransport or NaDC; H+ returns to the TF

Question 1

Three metabolic processes contributing to FIXED acid load (nonvolatile)

Answer 1

1. Oxidation of -SH groups => H2SO4
2. Hydrolysis of phosphoesters => H3PO4
3. Breakdown of carbs, fats => lactic acid (exercise), ketone bodies

Question 2

Bicarbonate Excretion

Answer 2

HCO3- enters the TF via HCO3-/Cl- antitransport during alkalosis

Question 3

Bicarbonate Replenishment

Answer 3

Occurs via 2 mechanisms:

1. Secretion of H+ ions; reabsorption of HCO3-
2. Catabolism of glutamine in the PT => secretion of NH3 and NH4+ into TF
   =>NH3 and NH4+ is reabsorbed in Henle’s Loop where it is secreted in the CD, reacts w/ other secreted H+ to become NH4+ and is excreted ;and HCO3- is reabsorbed

Question 4

Type-A intercalated Cells

Answer 4

Reabsorbs remaining filtered HCO3- in the DCT and also produces titratable acid

Question 5

Type-B intercalated Cells

Answer 5

Secretes HCO3- in the DCT

Question 6

NAE

Answer 6

“Net Acid Excretion”

NAE= (Urinary NH4 + titratable acidity - Urinary HCO3-)

NAE < 0 => Alkalosis

0 < NAE < 100 => Normal

NAE > 100 => Acidosis

Question 7

Altitude Sickness

Answer 7

Hypoxia stimulates hyperventilation causing low PCO2 levels and alkalosis

HCO3- will try to compensate by decreasing