Why are millions of sperm needed, while only one will fertilize the egg?

The battle that sperm cells give to fertilize the egg is merciless. They have no help from the female reproductive organs. The first obstacle is the cervix, a complex labyrinth that prevents many sperm from eventually entering. Those who finally succeed, have to go through a "hostile" uterus and be lead to a narrow entrance, the fallopian tube. Those which finally enter the tube - very few in number - eventually meet the egg.


In more detail:

Within 30-60 minutes of entering the vagina, 99% of the sperm will have died. Some millions will continue to move towards the dark side of the vagina. Here is where the woman's body helps, only during ovulation, by the releasing estrogens, therefore softening the hard mucus that clogs the cervix. Cervical mucus will drip into the vagina, extending the life of the remaining sperm. Now only a small percentage of sperm will continue (about 60,000). The difficult passage from the cervix leaves even fewer survivors. The cervix is ​​smart and selects only well-made sperm to move inward.


About 3,000 sperm will continue the journey to a small opening that leads to the fallopian tubes. Ovulation occurs from one side each month. Thus, when the egg will descend e.g. from the left ovary, the uterus makes muscle contractions from the left side, leading most of the sperm to that side.


The main purpose of the uterus is to accept the growing fetus (if the egg is fertilized). It is not designed to accept sperm or anything else. For this reason, the reaction of the female immune system will be to kill sperm because it sees them as invaders. In order to kill them, it uses thousands of leukocytes.


After thousands of sperm are killed, only a few dozen will be able to reach the entrance to the fallopian tube. Here, only skillful swimmers will pass, while everyone else will die. The 10 cm in the fallopian tube is the most friendly place so far for the few spermatozoa that had the correct molecular structure and managed to pass: from a few dozen to even 2-3 in number! Here it is believed that semen can live from hours to days. The purpose each one sperm is to wait for the egg to appear, and as soon as it does, it swims and tries to reach the inner core first, and thus seal its victory.


As soon as the sperm penetrates the egg, the tail will be left out and its head will literally explode! The victorious sperm will disintegrate directly as the male genetic material will be joined with the female DNA.


The female chromosomes will unite with the male ones and at this point a new life will form!



Source 1

Source 2



See all of our blog posts, by clicking here.