Some semen is absorbed into your vaginal lining, a very small amount. Most of it is expelled during a few hours after sex. Believe it or not our vaginas have an acidity balance that is capable of dissolving semen before it ever reaches your cervix. I asked my doctor this question and this is what he told me. Pretty interesting.
Most leeks out like normal and the rest is absorbed buy your body. Later in pregnancy it helps soften you'r cervix ready for labour