What happens to urine concentration during dehydration?

During dehydration, the body loses water, which leads to reduced fluid levels. To conserve water, the kidneys respond by reabsorbing more water from the filtrate as it passes through the nephron. This process is influenced by the hormone antidiuretic hormone (ADH), which increases the permeability of the collecting ducts in the kidneys to water. As a result, less water is excreted in the urine, and the urine that is produced becomes more concentrated. This higher concentration of solutes, such as urea and electrolytes, alters the urine's composition, leading to a darker appearance and increased specific gravity. Therefore, the correct answer reflects the physiological response of the body to dehydration, which is to conserve water and produce urine that has a higher concentration of solutes.