surgkhurram Says:

Apr 22, 2008 - Thanks for the videos. These videos are great. May I request you to make some basic general pathology videos on various basic general pathology topics like inflammation etc.

tapasimd Says:

Apr 29, 2008 - The descending limb is permeable to water and ascending limb permeable to sodium.Hence as sodium is pumped out of descending limb,the interstitial osmolarity increases and the water rushes out of ascending limb to return osmolarity to equilibrium.Hence fluid is concentrated most at the end of descending limb and least at the end of loop of henle,I think,Isn't it?

o2demand Says:

May 27, 2008 - Comment from indeedslim: No, the descending limb pumps out water and that concentrates the fluid in the lumen. This accounts for the concentration of the fluid in the lumen in the descending limb. Ions are pumped out in the ascending limb and that accounts for the decrease in the osmolarity in the ascending portion. The reason for the concentration gradient in the lumen is due to the vasa recta's absorption of the ions pumped out of the ascending limb of the LOH.

symplemplam Says:

Aug 9, 2008 - are you a doctor or something??

flaskhalss Says:

Sep 16, 2008 - Nothing ever pumps water. The descending limb pumps Na+ from the lumen, dragging the water with it. The ascending part of the loop is impermeable to water but pumps out ions. This is what creates the hyperosmolar medulla and hypo-osmolar fluid in the tubulus. The hypo-osmolor fluid then ascends into the cortex where the interstitium is iso-osmolar, allowing water to be diffuse back to the systemic circulation. Without this part there would be no hyperosmolar medulla.