Ascending loop of Henele has which transporter-
Ans. is 'b' i.e., Na+ - 2C1 - K+ cotransporter o The loop of Henle has a thin descending, a thin ascending and a thick ascending segments.Thin discending segment (limb)o This segment is highly permeable to water and relatively impermeable to solutes (sodium, chloride and urea).o Therefore, only water is reabsorbed from the thin descending limb of loop of Henle and the fluid in the descending limb becomes hypertonic.o In passing through descending limb, 15% of filtered water is reabsobed so that only 20% of filtered water enters the distal tubules (60-70% of water is reabsorbed in proximal tubules).o This water absorption is also obligatory and occurs through aquaporin-1 water channel.o No active secretion or reabsorption takes place in this segment.o How'ever, some urea is secreted, but this is due to passive diffusion of urea from the medullary' interstitium (not active secretion).Thin ascending segment (Limb)o This segment of loop of Henle differs from the descending limb in being much less permeable to water but is very much permeable to NaClo So, some NaCI reabsorption occurs from thin ascending limb, but not water.o Therefore, at the end of thin ascending limb, the tubular fluid becomes isoosmotic once again.o This segment is important only in juxtamedullary nephron as cortical nephrons do not have thin ascending limb or very short thin ascending limb.o Therefore, in most of the nephron (85%) ascending limb usually refers to thick ascending limb. Thick ascending segment (limb)o Thick ascending limb is almost totally impermeable to water.o However, this segment has a pump for active absorption of sodium.o Absorption of sodium and other solutes without absorption of wrater results in dilution of the tubular fluid and fluid coming out from thick ascending limb is hypotonic to plasma,o Therefore, ascending limb is also called diluting segment. 30% of filtered Na+ is reabsorbed in ascending limb (60% is reabsorbed in proximal tubule).o In the thick ascending limb, a carrier (Na+ K+ 2C1- transporter) transports one Na-, one K+ and two Cl- from the tubular lumen into the tubular cells.o This is another example of secondary active transport. From the cells Na' is actively transported to the peritubular interstitium, across the basolateral membrane, by Na+ K+ ATPase.o The K+ diffuses back into the tubular lumen and into the interstitium via ROMK and other K+ channels,o Some other ions are also reabsorbed e.g.. Calcium, bicarbonate and magnesium.
Na+ - Cl cotransporter
Na+ - 2C1 - K+ cotransporter
ENaC channel
Na+ - aminoacid cotransporter
Renal Tubular Reabsorption and Secretion