Acid Base Balance Flashcards
How many mmol of non-volatile acid per day does the body generate?
70 mmol
A buffer system has highest buffering capacity near its ____.
pKa
True or false: the kidneys divide 70 mMols of carbonic acid into its respective “acid” and “base” components. Then it excretes 70 mMols of the “acid” (proton) component into the urine. And transports the 70 mMols of the “base” (bicarbonate) back into the blood to neutralize the daily acid load.
True
Describe how bicarbonate is reabsorbed in the kidney tubules.
- Protons are secreted, they combine with the filtered bicarb to form carbonic acid (H2CO3).
- Extracellular carbonic anhydrase converts H2CO3 to H2O and CO2.
- CO2 diffuses into tubular cells.
- Intracellular carbonic anhydrase re-synthesizes carbonic acid.
- Carbonic acid dissociates into H+ and bicarb.
- Bicarb exits the cell into blood, the H+ is re-used (pumped back into the tubular lumen, cycle starts over).
Describe three ways in which the body deals with acidosis.
- Hepatic urea synthesis decreases, sparing bicarbonate (2HCO3- + 2NH4+ –> urea + CO2 + 3H2O).
- Renal metabolism of glutamine –> ammonia + a-KG –> 2HCO3- increases.
- Increased secretion of ammonia (NH3) buffers excess protons in the tubular filtrate –> excretion of NH4+
Describe three ways in which the body deals with alkalosis.
- Decreased bicarb reabsorption by the kidneys.
- Increased hepatic urea synthesis consumes bicarbonate.
- Kidney synthesizes glutamine (rather than converting it to ammonia + bicarb).
Where in the nephron does the majority (80%) of bicarbonate reabsorption occur?
PCT
What is the difference between respiratory acidosis and metabolic acidosis?
Both are characterized by a plasma pH below 7.35
In respiratory acidosis the primary imbalance is pCO2 > 45mmHg from not being able to blow off CO2 from the lungs.
In metabolic acidosis the primary imbalance in HCO3- < 22 meq from an increase in nonvolatile acids or loss of base from diabetes, diarrhea, or renal faiulre.
What is the difference between respiratory alkalosis and metabolic alkalosis?
Both are characterized by plasma pH above 7.45.
In respiratory alkalosis there is a primary imbalance of pCO2 < 35 mmHg from hyperventilation.
In metabolic alkalosis there is a primary imbalance of HCO3- > 26meq from loss of acid in vomit or dehydration.
What is compensation? What is the difference between partial and full compensation?
Compensation is when the kidneys try to balance an acid-base disorder. Partial is when pH is not completely restored to a normal range, and full compensation is when pH is restored to normal.
What effect does hypokalemia have on acid-base balance? Explain.
It causes alkalosis in the following three ways:
- Increases apical Na+/H+ exchange (Na+ in, H+ out) in PCT cells –> increased bicarbonate production and release to the basolateral side.
- Increases apical K+/H+ exchange; protons come from H2O + CO2 –> H+ + HCO3-, so more bicarbonate is released to the basolateral side.
- Elevates ammonia synthesis (protons are needed for this) –> more bicarbonate synthesis.
What effect does hyperkalemia have on acid-base balance? Explain.
It causes acidosis in the following ways:
- It inhibits ammonia synthesis –> lower acid excretion/increased retention of protons.
- Blocks ammonium reabsorption in the thick ascending loop of Henle –> less ammonia in the the medullary interstitium –> less excretion of protons –> renal tubular acidosis.
What does cortisol do to the kidneys?
- Enhances Na+/H+ exchange (enhances acid secretion)
- Inhibits phosphate reabsorption –> increased ability for anions to buffer secreted protons.
What does aldosterone do to the kidneys?
- Simulates the Na+/H+ exchanger in PCT cells –> more acid secretion, increased negative charge in lumen.
- Prolonged elevation of aldosterone –> depletion of K+ –> stimulation of acid secretion and alkalosis.
Name three mechanisms by which diuretics cause acidosis and explain how in each case.
- Inhibitors of carbonic anhydrase block acid secretion and block bicarb reabsorption.
- K+-sparing diuretics inhibit apical Na+ channels –> hyperpolarization in the tubular lumen –> decreased acid secretion.
- Aldosterone antagonists decrease acid secretion.
