Read How the Medulla Concentrates Urine
Opposite flows and selective permeability create a medullary gradient that lets the kidney conserve water.
Electricity questions depend on identifying charge, a conducting path and the condition that controls current or magnetic effect.
Build the gradient
Filtrate flows in opposite directions in the two limbs of Henle’s loop; blood does so in the vasa recta. Their close arrangement supports the medullary gradient. NaCl and urea contribute to the high inner-medullary osmolarity.
Recycle urea and track filtrate
Urea leaves the inner medullary collecting duct and can diffuse into the thin ascending limb. During dehydration, filtrate is dilute in the DCT, more concentrated in Bowman’s capsule, then in the cortical collecting duct, and most concentrated near the loop base.
Counter-current multiplication
The thick ascending limb actively transports NaCl but is relatively impermeable to water. This separates salt from water and builds the medullary osmotic gradient that later supports concentrated urine.
OlympIQ exam lens
- ✓Loop limbs and vasa recta have counter-current flow.
- ✓Medullary gradient: NaCl + urea.
- ✓Urea recycles into the thin ascending limb.
Counter-current multiplication establishes the gradient; the vasa recta helps preserve it.
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