Final answer:
Sperm can survive inside the uterus or rather, within the uterine tubes, for 3-5 days after ejaculation, giving them an opportunity to fertilize an oocyte if intercourse occurs prior to ovulation. Once sperm meet an oocyte, fertilization may occur, leading to the formation of a zygote. Without fertilization, the menstrual cycle continues with menstruation.
Step-by-step explanation:
How Long Does Sperm Live Inside the Uterus?
After ejaculation, sperm embark on a challenging journey through the female reproductive system. The transit of sperm starts in the vagina, where the majority face their first obstacle: the acidic environment. Survivors then face thick cervical mucus which may block their entry to the uterus. Yet another barrier is the phagocytic uterine leukocytes that destroy some of the sperm that manage to get through. Those that enter the uterine tubes are reduced to a few thousand viable cells. This journey to the uterine tubes typically takes between 30 minutes to 2 hours, assisted by uterine contractions.
Should sperm not immediately meet an oocyte, or egg, they can survive in the uterine tubes for 3-5 days. This implies that fertilization is possible if intercourse occurs a few days prior to ovulation since the sperm can live within the female reproductive tract waiting for an ovum. However, once the oocyte is released, it only survives for about 24 hours. Therefore, to result in fertilization, intercourse needs to happen ideally before or during ovulation.
Upon successful fertilization, a zygote is formed, which will develop into a new organism. However, if the sperm does not fertilize an egg, menstruation occurs, and the cycle begins anew. Sperm must swim considerable distances, relative to their size, to reach an egg, and their swimming journey is equivalent to around 192,000 times their length.