Post Date November, 16 2024
After entering the vagina, sperm must overcome a large number of obstacles in order to reach the fallopian tubes. The distance traveled by sperm is about 15 to 18 centimeters, and most of them cannot reach the egg. They die midway, and 99% of sperm are killed by acidic pH in the vagina.
The first obstacle: vagina
After sperm enters the vagina, it is an acidic pH environment and must escape quickly. The pH value of the vagina is low (acidic) at around 3-4, and sperm typically cannot survive for more than 1-2 hours in the vagina. This is an important defense mechanism that can protect women from the attacks of bacteria and viruses in daily life, and these acids can also quickly kill sperm. Within a few minutes after ejaculation, only the fastest and healthiest sperm can enter the relatively safe cervix, and sperm can survive in cervical mucus for at least two days. There are approximately 200 to 250 million sperm per ejaculation, but only about 1% of the sperm, which means that only about 1 million of the 2 million relatively safe cervix can enter the uterus. 99% of sperm remain in the vagina and die quickly.
Step 2: The uterus reaches the fallopian tubes
However, entering the cervix is only the beginning of the journey of sperm inside the female body, and the next step is how to cross the uterus and enter the fallopian tubes. Although this is a journey of only 10 to 12 centimeters, there are many dangers along the way, with 10000 sperm remaining to swim to the top of the uterus and only 5000 sperm moving towards the correct fallopian tubes.
Firstly, there are a large number of immune white blood cells in the uterus, which recognize sperm cells as antigens for attack.
Secondly, the issue of direction is whether to turn left or right. Women have two fallopian tubes, but the ovaries only release one egg per month. Sperm must swim to the correct fallopian tube in order to possibly encounter an egg, and there is nothing in the other direction.
Entering the fallopian tube again requires going through the narrowest part: the utero tubal junction, which is only a few sperm diameters wide and only about a few hundred carefully selected sperm can enter the fallopian tube.
Transparent tape reaction ensures that only one sperm enters the egg cell
As soon as sperm reach the fallopian tube, most of them lose their vitality and move forward further. Only a few sperm are still competing, with only a few dozen to two hundred sperm reaching the egg cell. Only one can enter the egg through the egg cell sperm, and the nuclei of the two fuse to complete the fertilization process. Afterwards, the zona pellucida reaction prevents other sperm from entering the egg cell.
