Question

The loop of Henle is considered an engineering marvel. If the loop were straight, what negative effect would it have on the normal functioning of the kidney? Give your answer with particular relevance to the different permeabilities for water and salt in the various regions of the nephron and how the countercurrent multiplier and countercurrent exchange systems help maintain the osmotic gradient across the cortical medullary axis of the kidneys.

Answer 1

Answer: If the loop of Henle were straight, means the filtrate would flow to bladder and then finally out of the body, approx >10 times of the total volume of extracellular fluids were lost each day. Because of the loop of Henle, the water and required solute are reabsorbed in the body by a mechanism called tubular reabsorption.

Different permeabilities for water and salt in the various regions of the nephron:

• Thin descending limb: It is water and small solute permeable.
• Thin ascending limb: This region is permeable to solutes but is water impermeable. which causes solutes to move out but water is retained in the tubule.
• Thick ascending limb: This region absorbs solutes like Na, K, an CL. it is impermeable to water. and here also water is retained.

Countercurrent multiplication: It is the process which helps in generating the osmotic gradient using the energy, Osmotic gradient helps in reabsorption of water from the fluid which is present in tubule and to produce concentrated urine. After fluid leaves the ascending limb of Henle it enters the distal convoluted tubule, where the concentration is adjusted before it drains out in collecting duct. Once the concentration is adjusted and it descends from collecting duct in the medulla, reaches the ureter, and then transported to the bladder.