Loop of henle, a part of nehron of kidney

Loop of henle

1. LOOP OF HENLE

2. Transport of Solutes Loop of henle reabsorbs about : 25% of filtered NaCl 30% of filtered Ca2+ 65% of filtered Mg2+

3. In Descending limb Descending limb is permeable to water. But it is impermeable to solutes The fluid in terminal part of descending limb becomes hypertonic as water moves out of the tubule to enter the interstitial space.

4. In thin ascending limb The transport mechanism is predominantly a passive phenomenon The permeability of water is less Though passive transport of NaCl occurs to some extent, active transport of Na+ is almost nil

5. In Thick Ascending Limb In the thick ascending limb of LOH, the fluid becomes more dilute (hypotonic) as Na+ and Cl- are taken out of the tubular fluid. The active transport system for Na + is well-developed in this segment. Reabsorption of Na+ from tubular fluid is dependent on 1Na+1K+2Cl- cotransporter membrane protein

6. . This carrier protein is present on the apical membrane which transports Na+ from lumen into the cells From tubular cells Na+ is transported into interstitial fluid by Na+K + pump K+ from cells diffuses back into the tubular fluid and also into the interstitium passively through ROMK and other membrane K+ channels.

7. Cl that enters the cell is cotransported with K' into the interstitial fluid. Transepithelial transfer of these solutes creates a potential difference between tubular and interstitial fluid space, which drives transfer of solutes, especially transport of Na, K, Mg", and Ca" via paracellular pathway.

8. Transepithelial transfer of these solutes creates a potential difference between tubular and interstitial fluid space, which drives transfer of solutes, especially transport of Na, K, Mg", and Ca" via paracellular pathway. Bartter syndrome : Defect in transport of solutes in the thick ascending limb of LOH due to mutation of gene Barttin

9. Reabsorption of water LOH reabsorbs 15% of filtered water This occurs exclusively in the descending limb The descending limb except at its terminal portion is highly permeable to water. In spite of active transport of solutes in thick ascending limb of LOH, water is not reabsorbed.

10. Both thin and thick portions of ascending limb of LOH are almost impermeable to water. Furosemide is a loop diuretic