On the woman's side, the mucous membranes that line the vaginal walls release fluids during intercourse so that the penis can slide with just the right amount of friction. As intensity and sensations build, the woman's brain tells the vagina and nearby muscles to contract. That contraction brings the penis in deeper and increases the chance of his sperm getting closer to the target. During an orgasm, the cervix, located at the top of the vagina, dips down like an anteater, and sucks semen in the cervix (the bottom of the uterus). The sperm is trapped in the cervical mucus until the release of the egg, and a signal then lets the sperm start the competitive swim up into the uterus.
Find out more about this book:YOU: Having a Baby: The Owner's Manual to a Happy and Healthy Pregnancy