Sketchy Path: Renal - "Renal Tubular Acidosis" Flashcards
Renal tubular acidosis is characterized by what lab finding?
Non-anion gap metabolic acidosis (like the acid truck with the CLOSED GAP)
Which cell type secretes acid into the collecting duct?
The intercalated cells (like the INTERnational food truck that is spilling acid into the canoe river)
Explain the pathophysiology of type 1 renal tubular acidosis.
Dysfunctional intercalated cells lead to failed secretion of H+, which then decreases the HCO3 in the blood (think of the broken INTERnational food cart with the guy with the SINGLE beaker by the acid)
What lab findings are characteristic of type 1 RTA?
- Hypokalemia due to impaired reabsorption of K+ (spilled bananas by river)
- Non-anion gap metabolic acidosis
- Elevated urinary pH (canoe with oar holders that are 5.5 in the blue alkaline water)
- Low urinary ammonium (guy with empty ammonium bucket)
By what mechanism do calcium phosphate stones form in RTA 1?
- Metabolic acidosis leads to increased bone resorption, leading to increased serum calcium and phosphate levels
- Alkaline urine causes the precipitation of stones
- Citrate is used to buffer blood, so it will be low in the nephron
(Think of the rocks with phosphate fossils in the river –the citrus crate cracked on them.)
Review the etiologies of type 1 renal tubular acidosis.
- Drugs: amphotericin, lithium (frog jumping in puddle and LIFTium chairlift above the river)
- Autoimmune disorders: RA, Sjögren’s (antibody lights on truck)
- Hereditary disorders (family)
- Hypercalciuric disorders (dad spilling ice cream on his crouch)
How is bicarb absorbed in the PCT?
Carbonic anhydrase converts H+ and HCO3- to CO2 and H2O, which pass through the membrane and into the cell. They then get converted back to H+ and HCO3-. H+ is secreted back into the lumen, while HCO3- is absorbed into the blood.
(Think of the CAR Battery on the bicarb bakery truck.)
Explain the pathophysiology of type 2 RTA.
The PCT fails to absorb bicarb and bicarb is lost in the urine (like the kids shaking the bicarb truck near the guy with TWO tubes of acid).
Why is type 2 RTA self-limited?
The metabolic acidosis is caused by loss of bicarb. When levels fall to around 15, the bicarb absorption picks up by later parts of the nephron and the acidosis stabilizes.
(Think of the LIMITED edition cupcakes with MORE LATER below.)
The lab findings of type 2 RTA include ________________.
• Hypokalemia (because the bicarb binds to Na which is carried to the collecting duct and exchanged for K+)
• Initially alkaline urine that becomes acidic due to enhanced bicarb absorption (like the blue puddles becoming yellow when the kid spilled lemonade on them)
•
When more than bicarb is not reabsorbed in the PCT, it is called ______________ syndrome.
Fanconi (like the fans with cones)
Review the etiologies of type 2 RTA.
- Fanconi syndrome
- Acetazolamide
- Expired tetracyclines
What is the cause of type 4 RTA?
Mineralocorticoid deficiency
Think of the crumbling mountain behind the four tubes.
The only RTA associated with hyperkalemia is ___________.
4
Think of the bananas in the trees.
Why does mineralocorticoid deficiency lead to acidosis?
Mineralocorticoid deficiency leads to hyperkalemia from failure to secrete K into the collecting duct. The rise in K leads to a shift of H+ from inside to outside cells. The shift outside causes an intracellular alkalosis. Cells think they’re alkalotic, so they stop making NH3, which is needed to get rid of H+.
(Think of the bananas falling on the guy’s head and causing him to spill acid; he also dropped his NH3 bucket.)
