Answer:
Sometimes, the kidneys have to produce concentrated urine because the fluids levels in the body are relatively low and the electrolyte concentration is high. This function is performed by the loop of Henle, which is a tube located in the nephrons that allows for urine concentration. It consists of a multiplier system in which fluids move up and down the tubes, transporting substances horizontally. This movement results in a higher concentration of substances at the bottom of the tubes. In this way, the mammalian nephron produces concentrated urine to conserve water and avoid desiccation. The length of the loop of Henle becomes longer to allow mammals to survive in desert habitats. When this change occurs, nephrons become juxtamedullary.
