Loop of henle

A question was asked earlier in class today about the structural function of the loop of Henle. When I tried to research the answer I found out that primary function of loop of Henle is to concentrate the urine and provide osmotic pressure. I found an article that was talking about a research on birds renal physiology. Birds are the only vertebrates that can produce urine more concentrated than their plasma. They want to examine the structure of loop of Henle in birds to see if that defines to ability to do that.