During arousal, histological changes include the dilation of blood vessels, increased blood flow, and the activation of glandular tissues. For instance, in the skin, arousal can lead to piloerection (goosebumps) due to the contraction of arrector pili muscles. In reproductive organs, changes include the engorgement of erectile tissues and the secretion of lubricating fluids from glands like the Bartholin's glands in females.