Final answer:
Sperm can survive in the female reproductive tract for about 3-5 days after ejaculation, with their journey to the uterine tubes typically taking 30 minutes to 2 hours. Fertilization is possible if intercourse occurs a few days before ovulation, as oocytes are viable for approximately 24 hours post-ovulation.
Step-by-step explanation:
The viability of sperm after ejaculation depends on the conditions they encounter. Inside the vagina, which is acidic (approximately pH 3.8), millions of sperm are neutralized. Moreover, thick cervical mucus can block many from entering the uterus, and phagocytic uterine leukocytes destroy thousands more. Sperm that manage to reach the uterine tubes have a journey time of about 30 minutes to 2 hours. If they do not encounter an oocyte quickly, sperm can nonetheless survive in the uterine tubes for about 3-5 days, thus allowing fertilization to occur if intercourse takes place a few days before ovulation. After ovulation, an oocyte can only survive for approximately 24 hours, making fertilization unlikely if intercourse occurs more than a day afterwards.
It is important to note that the process of sperm production is continuous throughout a male's life after puberty. However, factors such as age, lifestyle, and medical procedures like vasectomy can affect sperm counts and viability. For example, after a vasectomy, sperm are still produced but are reabsorbed instead of being ejaculated. Sperm production generally starts to decline after age 35, and habits like smoking can lower sperm counts irrespective of age.