loop of henle and countercurrent mechanism

what segment of the loop of henle is water permeable?

descending limb

where in the loop of henle is impermeable to solutes?

thin dsecending limb

what occurs in the ascending loop of henle?

actively reabsorbs NaCl to the tubular cell and then to medulla. Uses Na-K-2Cl symporters coupled to a Na-K pump to create a electrochemical gradient that causes to reabsorption of cations.

what is the function of the countercurrent mechanism in the loop of henle?

to reabsorb the remaining water and solutes from the filtrate

what are the components of the countercurrent system?

countercurrent multiplier system, recycling of urea, countercurrent exchanger system

what is the countercurrent multiplier system?

1. NaCl is actively transported from the filtrate in the thick ascending limb into the interstitial fluid, raising its NaCl concentration

2. the NaCl pumped into the interstitial fluid draws water out of the filtrate in the thin descending limb into the interstitial fluid by osmosis

3. due to the continuing loss of water, the NaCl concentration of the filtrate increases as it approaches the bottom of the loop

4. the high NaCl concentration of the filtrate that reaches the thick ascending limb allows the NaCl reabsorption to continue

what is urea recycling?

urea is reabsorbed form the collective duct and papilla ducts due to a high permeability and down its concentration gradient towards the interstitial compartment, which contributes even furter to increasing the osmolarity of the medulla

what is the function of urea recycling?

save sodium to concentrate the kidney medulla

what is the nephrons primary driving force for the countercurrent multiplier mechanism?

reabsorption of NaCl in the thick ascending limb

what is the stimulus for ADH?

high plasma osmolarity

what is the function of ADH?

causes the expression and translocation of aquaporins in the apical membrane of the collective ducts, promoting the reabsorption of facultative water towards the renal medulla