Lecture 13: Acid/Base Regulation Flashcards
Nonvolatile acids
Aka fixed acids. Must be metabolized/excreted e.g. lactic acid, sulfuric/phosphoric acids, keto acids, uremic acids
Possible sources of fixed acids
- Anaerobic glycolysis
- FA beta oxidation
- AA metabolism
- Nucleic acid oxidation
- Fecal base loss
Volatile acids
Capable of diffusing in and out of liquids, e.g. CO2
Net Endogenous Acid Production
Body NEAP = 15-20 mol volatile, 50-100 mmol nonvolatile acids per day; kidneys must be able to excrete nonvolatiles
Renal bicarb reabsorption
Bicarb is freely filtered and entirely reabsorbed
Proximal tubule reabsorption process for bicarb
No direct apical transporter; uses carbonic anhydrase and CO2/H2O diffusion
Collecting duct bicarb transport cell types
- Intercalated α cell = H+ secreting
- Intercalated β cell = bicarb secreting
Intercalated α cell H+ secretion process
Notice K+/H+ exchanger
Intercalated β cell bicarb secretion process
Active during alkalosis (get rid of bicarb)
Buffers for renal bicarb production
- Phosphate
- Ammonium
Why are buffers needed for renal bicarb production?
Buffers titrate the fixed acids from metabolism; reabsorbed bicarb is not sufficient alone
Bicarb production with phosphoric acid buffering
- HPO4(2-) is filtered out
- Cell makes H+, HCO3-
- H+ secretion titrade with the buffer
- New HCO3- absorbed to blood
- 1/3rd of acid load is excreted this way
Bicarb production/acid excretion with ammoniagenesis
- Glutamine metabolism makes bicarb and NH4+
- Bicarb is absorbed and NH4+ is secreted
- NH4+ reabsorbed in thick AL
- NH3 secreted later in CDs along with H+, making NH4+
- Accounts for 2/3rds of excreted acid load
Renal response to increased acid load
- Bicarb reabsorption
- Increased H+ excretion via titratable acid
- Increased H+ excretion via more NH4+ production
Acidosis/alkalosis vs acidemia/alkalemia
Acid/alkalosis refer to [H+]; acid/alkalemia refer to blood pH
How does the body counter disturbances in physiological pH?
- Buffering
- Compensation (metabolic, respiratory)
How does the body buffer pH?
ECF: bicarb
ICF: proteins/phosphates
How does the body compensate for pH?
Respiratory: change in ventilation
Renal: change in bicarb reabsorption, acid excretion, bicarb production
How are respiratory and metabolic acid/base disorders different?
Respiratory: based in changes in pCO2
Metabolic: based in changes in bicarb concentration
