🔬 Urinary System Lesson

G-PCT-LOH-DCT-CD: the nephron pathway in order

Each of the roughly 1 million nephrons per kidney processes filtrate through five sequential segments, each with a specialized job.

Glomerulus

PCT

Most reabs.

LOH

Concentrate

DCT

Fine-tune

Final H2O

📖 Full Breakdown

Five segments, and two nephron subtypes with different jobs

The length of a nephron's loop of Henle directly determines whether it specializes in bulk filtration or urine concentration.

Glomerulus

Filtration

A tuft of capillaries where blood pressure forces fluid into Bowman's capsule — the very first step in urine formation.

Proximal Convoluted Tubule (PCT)

The site of MOST reabsorption

Reclaims the bulk of glucose, amino acids, sodium, water, and bicarbonate — the workhorse segment for bulk reabsorption.

Loop of Henle

Descending and ascending limbs create a concentration gradient

This gradient is what ultimately allows the kidney to produce concentrated urine later in the pathway.

Distal Convoluted Tubule (DCT)

Fine-tuning, hormone-regulated

Aldosterone acts specifically here, adjusting sodium reabsorption and potassium secretion based on the body's current needs.

Collecting Duct

Final water reabsorption, ADH-dependent

The last opportunity to concentrate or dilute urine, controlled by ADH — connecting directly to the Fluid Balance lesson later in this section.

🩺 Clinical / Exam Application

A comparison between cortical nephrons (which handle most overall filtration) and juxtamedullary nephrons (which have unusually long loops of Henle) explains why the kidney can do two different jobs simultaneously: bulk filtration of blood and precise urine concentration. Because juxtamedullary nephrons' longer loops of Henle create a much stronger concentration gradient in the medulla, these specific nephrons are disproportionately responsible for the kidney's ability to produce highly concentrated urine when the body needs to conserve water — a specialized job that shorter cortical nephrons aren't as well equipped to do.

⚠️ Exam Alert

The distinction between cortical nephrons (most filtration) and juxtamedullary nephrons (long loops, urine concentration) is a frequently tested detail — exam questions may test which nephron subtype is responsible for the kidney's urine-concentrating ability specifically.

🚧 Common Trap

Don't assume all nephron segments reabsorb the same substances in equal amounts. The PCT handles the vast majority of reabsorption (glucose, amino acids, most water and sodium), while the DCT and collecting duct handle much smaller, but hormonally regulated and precisely adjustable, final amounts.

✅ Quick Check

Why do juxtamedullary nephrons, with their unusually long loops of Henle, play a disproportionate role in the kidney's ability to concentrate urine?

📝 Exam Prep

Common Exam Questions

❓ What is the pathway of filtrate flow through the nephron?

✅ Glomerulus (filtration) → Proximal Convoluted Tubule (most reabsorption) → Loop of Henle (concentration gradient) → Distal Convoluted Tubule (hormone-regulated fine-tuning) → Collecting Duct (final ADH-dependent water reabsorption).

❓ What is the difference between cortical and juxtamedullary nephrons?

✅ Cortical nephrons handle most of the kidney's overall filtration. Juxtamedullary nephrons have unusually long loops of Henle, giving them a specialized role in concentrating urine.