Question

Select the correct statement about fertilization.

A) Both spermatozoa and the ovulated secondary oocyte remain viable for about 72 hours in the female reproductive tract.
B) Millions of sperm cells are destroyed by the vagina's acidic environment.
C) If estrogen is present, the pathway through the cervical opening is blocked from sperm entry.
D) Once inside the uterus, most sperm cells are protected and remain viable.

Answer 1

Fertilization occurs when sperm and an oocyte combine, and their nuclei fuse. Sperm face many challenges and barriers on their journey to reach the oocyte in the uterus. Only a few thousand sperm out of millions released during ejaculation reach the uterine tubes, where the oocyte is typically encountered. These sperm can survive there for a few days, allowing fertilization to still occur even if intercourse takes place a few days before ovulation.

Step-by-step explanation:

Fertilization occurs when a sperm and an oocyte (egg) combine and their nuclei fuse. During ejaculation, hundreds of millions of sperm are released into the vagina. However, many sperm are overcome by the acidity of the vagina and blocked from entering the uterus by cervical mucus. Of those that do enter the uterus, thousands are destroyed by uterine leukocytes. Only a few thousand sperm reach the uterine tubes where they may encounter the oocyte. If the sperm do not encounter an oocyte immediately, they can survive in the uterine tubes for another 3-5 days. On the other hand, an oocyte can only survive for about 24 hours following ovulation. Therefore, fertilization can still occur if intercourse takes place a few days before ovulation.