USMLE Step 1 · Embryology & Anatomy

PCT and loop of Henle nephron functions vs DCT and collecting duct nephron functions

How to tell PCT and loop of Henle nephron functions and DCT and collecting duct nephron functions apart when a board question makes them look alike.

Fastest separator

PCT/loop are bulk reabsorption and gradient; DCT/collecting duct are hormone-regulated fine-tuning with NCC, ENaC, and AQP2.

Side by side

PCT and loop of Henle nephron functionsDCT and collecting duct nephron functions

Key clue

PCT handles most bulk reabsorption; loop of Henle uses descending water permeability and thick ascending NKCC2 salt reabsorption to build the medullary gradient.

DCT uses NCC and TRPV5 for salt/calcium handling; collecting duct uses ENaC/aldosterone and V2-AQP2/ADH to tune potassium, acid, and water balance.

Mechanism

PCT reabsorbs glucose, amino acids, bicarbonate, phosphate, and most sodium/water; thick ascending limb is water-impermeable and reabsorbs Na-K-2Cl through NKCC2.

DCT reabsorbs NaCl via NCC and calcium via TRPV5 under PTH; collecting duct principal cells use ENaC and AQP2, while intercalated cells regulate acid-base.

Labs and tests

Loop diuretics block NKCC2; PCT handles glucose and bicarbonate.

Thiazides block NCC; PTH increases TRPV5 calcium reabsorption; aldosterone increases ENaC; ADH inserts AQP2.

The trap

PCT bulk reabsorbs; loop builds gradient; DCT handles NaCl/calcium; collecting duct is aldosterone/ADH final tuning.

The repair move

Before naming the answer, force the stem through the separator: PCT bulk reabsorbs; loop builds gradient; DCT handles NaCl/calcium; collecting duct is aldosterone/ADH final tuning.

Try a free question

Core

A research team is studying nephron segment function. One nephron segment reabsorbs about 65% of filtered sodium and water, all of the filtered glucose and amino acids, and is the site of bicarbonate reclamation (with luminal CA driving CO2 absorption). Which nephron segment is this?

Show answer and explanation

Answer: A. Proximal convoluted tubule. PCT reabsorbs 65% of filtered Na+/water (isosmotic), 100% of filtered glucose (via SGLT2), 100% of amino acids, much of bicarbonate (luminal carbonic anhydrase converts filtered HCO3- to CO2, which diffuses into cell), phosphate (inhibited by PTH), and many other solutes. SGLT2 inhibitors (empagliflozin, etc.) block proximal glucose reabsorption. Acetazolamide inhibits PCT carbonic anhydrase.

Why the other choices are tempting

B. Thick ascending limb of loop of Henle reabsorbs Na+/K+/2Cl- via NKCC2 (target of loop diuretics like furosemide); generates the medullary concentration gradient.
C. DCT reabsorbs Na+/Cl- via NCC (target of thiazide diuretics).
D. Collecting duct principal cells reabsorb Na+ via ENaC (under aldosterone) and water via AQP2 (under ADH).
E. Collecting duct intercalated cells handle acid-base (type A secrete H+; type B secrete HCO3-).

Flashcards

Tap a card to flip it.

What clue supports PCT and loop of Henle nephron functions?

Choose PCT and loop of Henle nephron functions when the stem gives this pattern: PCT reabsorbs most filtered solute, bicarbonate, glucose, amino acids; loop of Henle creates medullary gradient with descending water and ascending salt handling.

What clue supports DCT and collecting duct nephron functions?

Choose DCT and collecting duct nephron functions when the stem gives this contrasting pattern: DCT reabsorbs sodium chloride and calcium under PTH; collecting duct responds to aldosterone and ADH for sodium, potassium, acid, and water balance.

Quick answers

What is the fastest way to tell PCT and loop of Henle nephron functions from DCT and collecting duct nephron functions?