Final answer:
Vasocongestion during sexual excitement affects the nipples, vestibular bulb, labia, phaluus, and wall of birth canal, resulting in their engorgement with blood. This process is controlled by parasympathetic nervous system activation which causes vasodilation of erectile tissues.
Step-by-step explanation:
During sexual excitement, various structures experience vasocongestion, which is the increased blood flow that causes tissues to become engorged. In both men and women, the nipples, vestibular bulb, labia, and phallus are directly affected by this process. Specifically, in males, vasocongestion leads to the swelling of the corpora cavernosa and corpus spongiosum within the phallus. Meanwhile, in females, the vestibular bulb, labia, and the wall of birth canal undergo similar changes, with increased blood flow resulting in engorgement and lubrication. Engorgement and lubrication of erectile and vaginal tissues serve to facilitate intercourse.
During the excitement phase of sexual response, acetylcholine released by postganglionic parasympathetic fibers causes the vessels in the erectile tissue to dilate, which in turn, leads to the engorgement of the affected tissues. This physiological change is crucial for sexual intercourse as it prepares the reproductive organs for copulation.