Our bodies have a system to tell us when we need food.
When a man becomes aroused, the blood vessels in his genitals dilate. This stimulates nerve endings, and increases sensitivity.
When a woman becomes aroused, the blood vessels in her genitals dilate.
In your skin, the hair follicles have little bags of oils, or sebum, to keep skin moisturized.
Sometimes, the blood vessels around the intestine become swollen and red. This causes discomfort.