Topics:
Animal Physiology, Animal Refresher
Correct Statement About Loop of Henle Permeability
Which statement about the loop of Henle is correct?
- Descending limb is permeable to water & impermeable to solutes
- Ascending limb (thin + thick) is permeable to solutes & impermeable to water
- Both statements are correct — Correct Answer
- Both statements are wrong
Explanation:
Correct Answer: Both statements are correct
The loop of Henle has distinct permeability properties in its two limbs that are essential for the countercurrent multiplication mechanism of urine concentration.
Descending Limb Properties
- Permeable to water — water exits the tubule by osmosis into the hypertonic medullary interstitium
- Impermeable to solutes — NaCl and urea do not cross the descending limb wall
- Net effect: Tubular fluid becomes progressively more concentrated (hyperosmotic) as it descends
Ascending Limb Properties (Thin + Thick)
- Permeable to solutes — NaCl is reabsorbed (passively in thin limb, actively via NKCC2 in thick limb)
- Impermeable to water — water cannot follow the solutes; tubular fluid becomes dilute
- Net effect: Tubular fluid becomes progressively less concentrated (hypoosmotic) as it ascends
Why This Matters: Countercurrent Multiplication
These opposing permeability properties create the medullary osmotic gradient (300–1200 mOsm/kg) needed to concentrate urine in the collecting duct when ADH is present. The hairpin loop arrangement multiplies a small osmotic difference into a large gradient along the medulla.
📚 About this Topic — Animal Physiology
This multiple choice question is from Animal Physiology, Animal Refresher. It has 4 options with a detailed explanation of the correct answer. Practice more MCQs from Animal Physiology to strengthen your preparation.
