It concentrated the interstitium so that there is a higher concentration, a higher hypertonicity in the outside than on the inside. Now, the next question is what exactly is the function of aldosterone? So we saw that ADH is responsible for producing these aquaporums, and we'll discuss that in more detail in just a moment. But what exactly the function of aldosterone? Well, aldosterone doesn't actually directly increase the flow of water from our collecting duct. What it does is it stimulates the production of sodium channels on the apical side of our epithelial cells.