1-how does the osmolarity of the kidney interstitial fluid change from the cortex to the inner medulla? why is this important? 2-• in the medulla, the solute concentration is high which allows water to diffuse out of the loop of henle through osmosis. the vasa recta capillaries are also in the medulla. how does their solute and water concentration change along the loop?

Osmolarity of the kidney’s interstitial fluid increases from the cortex to inner medulla. This ensures that there is a concentration gradient that allows for osmosis to take place along the kidney tubules in a kind of countercurrent flow exchange system. This way most, amount of water can be reabsorbed.

The same occurs in the loop of Henle in a process called countercurrent multiplication. The descending loop actively takes up solutes hence making the blood plasma in the the vasa recta highly concentrated. In the ascending loop, therefore, water in the tubules is reabsorbed by osmosis hence making urine more concentrated as it gets to the bladder.