Heterosexual intercourse occurs whenever a man puts his penis into a woman’s vagina. That’s the minimal definition. But sex is about more than that simple act. As such, you may be curious, or you may want to know how to describe sex to a teenager. The information below explains what — exactly — happens during intercourse.
When a man becomes aroused, the nerves surrounding his penis become active, causing the muscles around the arteries to relax and more blood to flow into the penis. The additional blood makes the penis stiff and hard, or erect. This erection tightens the veins so the blood can’t leave the penis, enabling the penis to remain erect.
When a woman becomes aroused, the vaginal lips and clitoris swell, the nipples on her breast become erect, and the vaginal walls fill with blood. The vagina becomes lubricated, or slippery, by the passage of fluids through the vaginal walls.
The man will usually insert his penis into the woman’s vagina after the above processes have begun. (It is difficult, although not impossible, to insert a flaccid penis into a vagina. Similarly, vaginal lubrication makes the process much easier.)
The sensual pleasure of sex comes in large part from the movement of the penis (generally in a thrusting motion) in the vagina. This pleasure increases until orgasm is reached — although orgasm may come at different times for the two partners or perhaps only for one partner. Orgasm comes with increased blood pressure, heart rate, and strong contractions in the genitals. For men, this is immediately followed by ejaculation.
After a man ejaculates or if his arousal fades, detumescence occurs, in which the brain sends a signal to allow the blood to leave the erect penis, and it returns to its flaccid state.
