Step by Step
G/B
Glomerulus and Bowman's capsule — filtration
The renal corpuscle consists of the glomerulus (a capillary tuft) surrounded by Bowman's capsule — this is where filtration actually occurs, separating filtrate from blood cells and large proteins.
PCT
Proximal convoluted tubule — bulk reabsorption
The PCT reabsorbs the bulk of filtered material: 65% of sodium and water, ALL of the glucose, amino acids, and a large portion of bicarbonate.
Loop
Loop of Henle — creating the concentration gradient
The descending limb is permeable to water but not solutes; the ascending limb is permeable to solutes but NOT water. This asymmetry is what creates the hypertonic medullary gradient, covered in more depth in a later lesson.
DCT/CD
Distal convoluted tubule and collecting duct — fine-tuning
The DCT fine-tunes reabsorption, with aldosterone acting here to control sodium/potassium exchange. The collecting duct handles final water reabsorption, controlled by ADH, before urine passes through the medulla, papilla, and calyx on its way out.
Types
Two types of nephrons
Cortical nephrons (85% of all nephrons) have short loops of Henle; juxtamedullary nephrons (15%) have long loops extending deep into the medulla, giving them a greater role in concentrating urine.
Applied Walkthrough
1
Blood enters the glomerulus, where filtration occurs across into Bowman's capsule — producing a protein-free filtrate that then enters the proximal convoluted tubule.
2
In the PCT, the bulk of filtered sodium, water, glucose, and amino acids are reabsorbed back into the blood — glucose reabsorption here is essentially complete under normal conditions.
3
The remaining filtrate flows through the loop of Henle, where the descending limb allows water to leave (but not solutes) and the ascending limb pumps out solutes (but remains impermeable to water) — together creating the concentrated medullary environment needed to concentrate urine later.
4
Finally, the DCT fine-tunes sodium and potassium levels (under aldosterone's influence), and the collecting duct makes final adjustments to water reabsorption under ADH's control, before the resulting urine exits through the renal papilla and calyx.
Exam Application
Exams test whether you can correctly sequence the six nephron segments (glomerulus → Bowman's capsule → PCT → loop of Henle → DCT → collecting duct) and match each to its primary function, and whether you know the difference between cortical and juxtamedullary nephrons.
⚠ Common Trap
The most common trap is assuming both limbs of the loop of Henle behave the same way — the descending limb is permeable to water only, while the ascending limb is permeable to solutes only (impermeable to water) — this asymmetry is exactly what creates the medullary concentration gradient.
✓ Quick Self-Check
1. Where does filtration occur in the nephron?
At the renal corpuscle — the glomerulus and Bowman's capsule.
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2. What does the PCT reabsorb in bulk?
65% of sodium and water, all of the glucose and amino acids, and a large portion of bicarbonate.
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3. What is the key difference between the descending and ascending limbs of the loop of Henle?
The descending limb is permeable to water (not solutes); the ascending limb is permeable to solutes (not water).
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4. What hormone acts on the DCT to control sodium/potassium exchange?
Aldosterone.
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5. What percentage of nephrons are cortical versus juxtamedullary, and how do they differ?
85% cortical (short loops) and 15% juxtamedullary (long loops extending into the medulla, more involved in concentrating urine).
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