REABSORPTION & SECRETION IN LOOP OF HENLE

REABSORPTION & SECRETION IN LOOP OF HENLE

3 parts-

* Thin descending segment/limb.

* Thin ascending segment/limb.

* Thick ascending segment/limb.

1. REABSORPTION IN THIN DESCENDING LIMB:

Water reabsorption:

* Highly permeable to water.

* Occurs through aquaporin -1.

* Obligatory type of reabsorption.

* 15% filtered water reabsorbed.

Reabsorption of solutes:

* Impermeable to solutes (Na²⁺, Cl^– & urea).

* Minimal urea secreted-

* Due to passive urea diffusion from medullary interstitium.

* No active secretion/reabsorption.

* Tubular fluid in descending limb – Hypertonic.

2. REABSORPTION IN THIN ASCENDING LIMB:

* NaCl^– reabsorption occurs –

  – Due to high NaCl^– permeability.

* Less permeable to water.

* Tubular fluid is iso-osmotic.

3. REABSORPTION IN THICK ASCENDING LIMB:

Sodium, Potassium & Chloride reabsorption:

* By “Secondary active transport” –

  – Through Na²⁺-K⁺-2Cl^–– carrier transporter.

  – Transports one Na²⁺, one K⁺, & two Cl^-.

  – Active sodium absorption occurs.

* 30% filtered Na²⁺ reabsorbed.

Water reabsorption:

* Totally impermeable to water.

Ascending segment also referred “Diluting” segment:

* Due to sodium & solute absorption without water.

* Resulting in tubular fluid dilution.

* Tubular fluid is hypotonic.

OTHER REABSORPTION:

* Calcium, Bicarbonate & Magnesium.

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