Renal tubule segment function - reabsorption/secretion site mapping (drugs, hormones, electrolytes)
Core concept
| Segment | Handles | Transporter | Acts here |
|---|---|---|---|
| PCT | 65-70% Na + water, all glucose, ~85% HCO3, 80-90% phosphate, all amino acids, 70% Ca | NHE3, SGLT2, NaPi-IIa | SGLT2i, acetazolamide, PTH and FGF-23 (phosphaturic) |
| Thin descending limb | Water only | AQP1 | - |
| Thick ascending limb | 25% Na, 20% Ca and Mg paracellular | NKCC2 + ROMK -> lumen-positive PD | Loop diuretics; CaSR |
| DCT | 5-7% Na, active Ca | NCC, TRPV5 | Thiazides, PTH |
| CD principal cell | 2-3% Na, secretes K, water | ENaC, ROMK, AQP2 | Aldosterone, ADH; blocked by amiloride, trimethoprim, spironolactone; ANP |
| CD alpha-intercalated | Secretes H+, reabsorbs K and HCO3 | H+-ATPase, H/K-ATPase | Fails in type 1 RTA |
| CD beta-intercalated | Secretes HCO3, reabsorbs H+ | Pendrin | Metabolic alkalosis |
- Impermeable to water: thick ascending limb (the "diluting segment") and DCT - this is what allows a dilute urine
3 more sections, plus exam facts
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