BiologyExcretory products and their eliminationClass 11Class 12

Nephron & counter-current mechanism: interactive simulation

Human kidneys can produce urine nearly four times concentrated than the initial filtrate (up to 1200 mOsm/L compared to 300 mOsm/L of blood plasma). This remarkable feat is achieved by the counter-current mechanism between Henle’s loop and the vasa recta.

Useful for: NEET, AIIMS, CBSE Boards

Try this

The flow of filtrate in the two limbs of Henle’s loop is in opposite directions and forms a counter-current. Similarly, blood flows in opposite directions in the two limbs of vasa recta. Henle’s loop acts as the active Multiplier, while Vasa Recta acts as the passive Exchanger that preserves the medullary gradient without washing it away.

  1. 1

    Click on the Descending Limb and compare it with the Ascending Limb.

    What you should see

    Descending limb is permeable to water and impermeable to electrolytes (filtrate concentrates to 1200). Ascending limb is completely impermeable to water and actively pumps NaCl out (filtrate dilutes to 200 mOsm/L).

  2. 2

    Drag the ADH / Vasopressin slider from 10% (overhydrated) to 90% (dehydrated).

    What you should see

    At high ADH, aquaporins open in the collecting duct; water rushes out into the hypertonic medulla, producing small volume of 1200 mOsm/L concentrated urine. At low ADH, large volume of dilute urine exits (Diabetes Insipidus).

  3. 3

    Turn on Vasa Recta and observe the blood flow arrows.

    What you should see

    Blood flows DOWN in descending vasa recta (next to ascending Henle) and UP in ascending vasa recta (next to descending Henle). It passively absorbs NaCl on the way down and returns it on the way up, preserving the gradient.

  4. 4

    Locate the purple Urea recycling arrow at the bottom of the collecting duct.

    What you should see

    A small amount of urea diffuses out of the collecting duct into the medullary interstitium, enters the thin ascending limb, and recirculates to sustain the 1200 mOsm/L hypertonicity.

Formulas behind it

Net Filtration Pressure (NFP)

Pnet=PG−(ΠG+PB)≈10 to 20 mmHgP_{\text{net}} = P_G - (\Pi_G + P_B) \approx 10\text{ to }20\text{ mmHg}

Glomerular Filtration Rate (GFR)

GFR=125 mL/min=180 L/day\text{GFR} = 125\text{ mL/min} = 180\text{ L/day}

Urine Concentration Ratio

Max Urine OsmolarityPlasma Osmolarity=1200300=4×\frac{\text{Max Urine Osmolarity}}{\text{Plasma Osmolarity}} = \frac{1200}{300} = 4\times

Reabsorption Percentage in PCT

≈70–80% of electrolytes and H2O (Isotonic)\approx 70\text{–}80\%\text{ of electrolytes and }H_2O\text{ (Isotonic)}

Common mistakes

  • Thinking Loop of Henle is the exchanger. Henle’s loop is the Counter-Current MULTIPLIER (active); Vasa Recta is the Counter-Current EXCHANGER (passive).
  • Thinking the ascending limb is permeable to water. The ascending limb is completely impermeable to water.
  • Assuming filtrate exiting Henle’s loop is concentrated. Filtrate leaving the thick ascending limb is actually HYPOTONIC (~200 mOsm/L) because salt was actively pumped out.
  • Confusing Cortical vs Juxtamedullary nephrons. Juxtamedullary nephrons have long loops of Henle dipping deep into the inner medulla with well-developed vasa recta, essential for concentrating urine.
Practise 7 questionsCheck your answer instantly, with a worked solution.Stuck on a nephron & counter-current mechanism question?Snap it and get a whiteboard video solution.

FAQ

Why does the medullary osmolarity increase from 300 to 1200 mOsm/L?

The gradient is established primarily by active transport of NaCl by the thick ascending limb of Henle into the medullary interstitium, augmented by urea recycling from the inner medullary collecting duct.

What role does Vasa Recta play in counter-current mechanism?

Vasa recta acts as a counter-current exchanger. Its sluggish hairpin blood flow allows it to supply oxygen to medullary tissues while preventing the rapid removal of NaCl and urea, thus preserving the medullary osmotic gradient.

How does ADH (Vasopressin) regulate urine concentration?

When dehydrated, osmoreceptors in the hypothalamus trigger the release of ADH from the neurohypophysis. ADH inserts water channels (Aquaporin-2) in the DCT and collecting duct, causing maximum water reabsorption into the hypertonic medulla.

What is Diabetes Insipidus?

Deficiency of ADH (or kidney insensitivity to it) leads to inability to reabsorb water in collecting ducts, producing massive quantities of dilute urine (polyuria) and extreme thirst (polydipsia).

Related simulations

All 65 simulations
Cell explorerBiology, Class 8 & Class 9 & Class 11Human heart and blood flowBiology, Class 10 & Class 11DNA double helixBiology, Class 12Mitosis step by stepBiology, Class 9 & Class 11Sliding filament theory & muscle contractionBiology, Class 11 & Class 12Action potential & synaptic transmissionBiology, Class 11 & Class 12

Want a specific topic or simulation added?

Tell us in our feedback box which chapter or concept you want visualised next.

Send feedback