Final answer:
When a person is dehydrated, ADH secretion increases to conserve water, leading to concentrated urine and reduced urine volume.
Step-by-step explanation:
Dehydration triggers a physiological response in the body that increases the secretion of antidiuretic hormone (ADH) from the neurohypophysis, or posterior pituitary gland. When a person is dehydrated, the blood becomes more concentrated, which is sensed by osmoreceptors. This leads to a rise in ADH levels, causing the kidneys to reabsorb more water, producing a smaller volume of more concentrated urine. Such urine is typically darker in color due to higher concentrations of wastes. The increase in ADH helps conserve water in the body, minimizes further dehydration, and assists in restoring normal blood osmolarity.