L11 Acid-Base Balance Flashcards
- pH = ___
- typical physiological pH range = ______
- ideal plasma pH = ___
- 10-fold change in [H⁺] for ___ pH unit of change
- pH = -log[H⁺]
- typical physiological pH range = 6.8 - 7.8
- ideal plasma pH = 7.4
- 10-fold change in [H⁺] for 1 pH unit of change
processes → state
- ___ (generating acid) → ___
- ___ (generating base) → ___
processes → state
- acidosis (generating acid) → acidemia
- alkalosis (generating base) → alkalemia
reactions that generate endogenous acid? (4)
what is serum CO₂ closely linked to?
what are the effects of dialysis on CO₂?
- acids constantly generated in the body, gets titrated with bicarbonate → secreted in lungs as CO₂
- oxidation of organic sulfur to SO₄²⁻
- conversion of neutral foodstuffs to organic acids
- hydrolysis of phosphoesters
- serum CO₂ ~ plasma bicarbonate closely linked
- dialysis: large spike in CO₂, then decreases as body generates acid which consumes bicarbonate
- bicarbonate/CO₂ : main physiological ___ in plasma
- reaction
- Henderson-Hasselbalch equation: pH ______ = ______
- [HCO₃⁻] can be used to determine if someone has ___ ___ or ___ ___
- bicarbonate/CO₂ : main physiological buffer in plasma
- CO₂ + H₂O ⇆ H₂CO₃ ⇆ HCO₃⁻ + H⁺
- Henderson-Hasselbalch equation: pH = pK + log (HCO₃⁻ / CO₂) = pK + log (HCO₃⁻ / sPCO₂)
- [HCO₃⁻] can be used to determine if someone has metabolic acidosis or respiratory acidosis
Isohydric principle:
- when there’s different buffers in a solution, all equilibrate @ a pH according to their relative pKa
- rarely have just bicarbonate in solution (phosphate…)
- can use pH to calculate basic + acidic forms of each buffer in solution
plasma anion gap = ?
what is it a measure of?
- plasma anion gap = [Na⁺] - ([HCO₃⁻] + [Cl⁻]) = unmeasured anions (mEq/L)
- exaggerated in certain physiological states (ex. fasting → break down fats → generate different fatty acids → anion gap gets larger)
- measure of metabolic status
2 strategies for acid-base handling utilizing bicarbonate?
1st: in proximal tubule? in late distal tubule/ CCD?
2nd: 2 strategies? 2nd in proximal tubule? CCD?
- recapturing bicarbonate from ultrafiltrate
proximal tubule
- HCO₃⁻ freely filtered → filtrate [HCO₃⁻] ~= plasma [HCO₃⁻]
- most HCO₃⁻ is reabsorbed by CO₂, which is coupled to the secretion of protons (via NHE3 or H⁺ ATPase)
- cell-attached carbonic anhydrase converts HCO₃⁻ → diffuses in as CO₂ → converted back to HCO₃⁻ by carbonic anhydrase II inside the cell → if HCO₃⁻ accumulates: 1 CO₂ + 1 HCO₃⁻ leave the cell via the Na/HCO₃⁻ cotransporter
late distal tubule / CCD:
- A/α - H⁺ secreting intercalated cell: H⁺ pumps use energy to transport H⁺ into the lumen + K⁺/H⁺ exchanger
- B/β-type HCO₃⁻ secreting intercalated cell: secretes HCO₃⁻ into the lumen in exchange for Cl⁻
- synthesizing new bicarbonate
a. titrable acid excretion
- use titratable acid (phosphate) to bind H⁺ → trapped in the lumen → excreted
- maintains driving force to keep secreting protons into the lumen
- rate of secretion ≠ rate of excretion
b. NH₄⁺ excretion
- proximal tubule: glutamine is metabolized by cells → 2 NH₄⁺ generated → some change to NH₃ → traverse into tubular fluid → bind to H⁺ → secreted into lumen
- collecting duct: NH₄⁺ enters → effluxes as NH₃ → binds to H⁺ → excreted into the urine
Rhesus protein (RhCg)
- mediates transport for ___ to be transported at ___ rates physiologically
- Rh__g + Rh__g on basolateral side, Rh__g on apical side
- like urea, interstitial ammonia concentration ___ as you go down into medulla
- mediates transport for ammonia to be transported at high rates physiologically
- RhBg + RhCg on basolateral side, RhCg on apical side
- like urea, interstitial ammonia concentration increases as you go down into medulla
net acid excretion formula vs total acid secretion formula
what happens with both in the case of metabolic acidosis?
net acid excretion = urine NH₄⁺ + titratable acidity - urine HCO₃⁻ → gives measure of buffer capacity of urine
total acid secretion = HCO₃⁻ reabsorbed + urine NH₄⁺ + titratable acidity
paradox! metabolic acidosis: net acid excretion increases but total acid secretion may decrease… because bicarbonate is being reabsorbed to buffer acids
acid-base disorders
