Changes

==Countercurrent System==

==Countercurrent System==

As the thin descending limb makes its way into the medulla the surrounding tissue becomes ever increasingly hypertonic and therefore the osmotic gradient increases the deeper the limb goes.  As the limb is permeable to water it leaves the tubule via [[Osmosis - Physiology| osmosis]].  The tube then bends back on itself and heads back up the cortex.  The thin ascending limb is entered. Here salt enters the tubule passively due to the hypertonicity of the medulla creating a gradient.  This results in a very high salt concentration at the bottom of the loop.  The fluid moves on and enters the thick ascending limb.  This has salt transporters and so salt is pumped into the medulla via active transport causing more water to leave the thin descending limb.  The [[Vasa Recta - Anatomy & Physiology | Vasa recta]] has a similar countercurrent uptake system and only removes what is absorbed maintaining the medulla in a hypertonic state.

As the thin descending limb makes its way into the medulla the surrounding tissue becomes ever increasingly hypertonic and therefore the osmotic gradient increases the deeper the limb goes.  As the limb is permeable to water it leaves the tubule via [[Osmosis - Physiology| osmosis]].  The tube then bends back on itself and heads back up the cortex.  The thin ascending limb is entered. Here salt enters the tubule passively due to the hypertonicity of the medulla creating a gradient.  This results in a very high salt concentration at the bottom of the loop.  The fluid moves on and enters the thick ascending limb.  This has salt transporters and so salt is pumped into the medulla via active transport causing more water to leave the thin descending limb.  The vasa recta has a similar countercurrent uptake system and only removes what is absorbed maintaining the medulla in a hypertonic state.