Distribution of Henle's loops may enhance urine concentrating capability.

A simple mathematical model that was developed by Charles S. Peskin (unpublished manuscript) for a single nephron is introduced and then extended to reflect the decreasing loop of Henle population as a function of increasing medullary depth. In the model, if all the loops turn at the same depth, the concentrating capability is limited by a factor of e over plasma osmolality. However, a decreasing loop population causes a multiplier effect that greatly enhances the concentrating capability. Using the loop distribution of the rat, the model produces a sigmoidal osmolality profile similar to the profiles found in tissue-slice studies of rat kidneys. These model calculations suggest that the decreasing nephron population found in vivo may be an important factor in the concentrating mechanism of the mammalian kidney.