The ultimate goal of sperm is to fertilize the oocyte. However, to get there, he has to go through a long and expensive journey. Many wonder how is this trip of the spermatozoon from ejaculation to fecundation. In this article, we detail it.
Below you have an index with all the points that we will discuss in this article.
The race of sperm
Colloquially the path to fertilization is understood as a race in which only the most skilled sperm will reach the goal and win the championship. Indeed, it is something like this: many sperms start the race, but only one is chosen to fertilize the egg.
We can divide the journey into two major stages:
- Male reproductive system: from the testicles to the outside.
- Female reproductive system: from the vagina, where the semen is deposited, to the fallopian tubes, where the ovule is located.
In each of these phases, the sperm encounters certain obstacles. Here we tell you what they are.
The path from the testicle to the urethra
The sperm takes about 90 days to develop and acquire the necessary maturation to be expelled in the ejaculation. They are born in the seminiferous tubules of the testicles and later pass to the epididymis.
The seminiferous tubules are the internal structures of the testicle where sperm are formed. The epididymis is an elongated structure that connects the testicle and the vas deferens.
At the time of intercourse, a large sperm (about 250 million) leaves the epididymis and passes through the vas deferens and the urethra. In this way, the spermatozoa are covered with the fluids released by the seminal vesicles and the prostate. This is how semen is formed, also known as sperm.
The main function of these fluids is to facilitate the entry of sperm into the vagina. The urethra will be fired through the penis until they enter the female reproductive system, specifically in the vagina.
During this journey from the testicle to the outside, the sperm acquires the exact shape to fertilize the ovule. The changes that occur in this final stage of sperm maturation are:
- Compact your DNA to allow the head (where the DNA is stored) to be as small as possible and able to move better and traverse the zona pellucida (egg cover).
- The tail acquires the perfect design for the sperm to have great strength and speed.
- The middle piece has a high amount of mitochondria to keep the energy at a high level. This offers the sperm great efficiency in the consumption of energy.
Tour of the female reproductive system
In ejaculation, sperm leaves the man and enter the vagina, from where they begin the second part of their journey to fertilization.
During this path, they encounter many obstacles or barriers that will hinder their arrival to the fallopian tubes, where the egg is located.
This entire journey is approximately between 15 and 18 cm and time is against. The sperm cannot be delayed much because the ovum, once it has left the ovary (that is, after ovulation ), has a half-life of about 24 hours. The survival time is short compared to that of the sperm, which can live between 2 and five days in the female reproductive system.
After the ejaculation, a race begins not only of speed but also of resistance. Defective and poorly mobile sperm will get in the way.
Some barriers that sperm encounter are:
- the pH of the vagina
- The vagina has an acidic pH, in which not all sperm can survive.
- Immunological action white blood cells of the woman detect the sperm cells as unfriendly and try to destroy them.
- Cervical much cervical secretions and vaginal discharge vary in texture and consistency throughout the female cycle. At the time of ovulation, this fluid is more fluid and less dense to allow the passage of sperm. However, outside the period of ovulation, it is a dense and viscous fluid that complicates the advancement of sperm.
- The female reproductive organ (vagina, cervix, uterus, fallopian tubes) is an obstacle for sperm. There are numerous cavities known as crypts in which many sperms are stranded.
But not all are difficulties. The ovum tries to pave the way for sperm by releasing molecules and sending signals. The fallopian tubes and the uterus exert a suction force through rhythmic contractions, and the cervical mucus becomes less dense, allowing the sperm to swim better.
The seminal fluid that accompanies the sperm neutralizes the pH and offers sugars to the sperm. This fluid serves as a protective shield against white blood cells.
Arrival to the fallopian tubes
Once the vaginal, cervical, and uterine barriers have been overcome, we find the route’s narrowest part: the uterotubal junction. Up to this point, only a few thousand of the 250 million sperm cells that were on average in the newly ejaculated sperm arrive.
Throughout the journey, the strongest sperm, those who have overcome female obstacles, acquire an extraordinary ability: fertilization. It is what is known as sperm hyperactivation. From this moment, its tail moves with much more force and energy, allowing a vigorous movement that facilitates the ovum’s arrival.
Once they reach the fallopian tubes, many sperms remain attached to the walls, exhausted and unable to follow the path.
At this point, there are few sperms left in the race because the vast majority have been lost along the way. Of the few tens of sperm that remain before the watchful eye of the ovule, only one will manage to cross the thick entrance door to the ovule: the zona pellucida.
The chosen spermatozoon, the strongest and trained, in contact with the zona pellucida, initiates the so-called acrosome reaction. It consists of releasing the content of the acrosome: a series of enzymes that weaken the zona pellucida and facilitate penetration.
This reaction “wakes up” the egg, releasing the cortical granules and organelles that prevent any other sperm from penetrating. It is as if the ovule planted a flag indicating the rest of the sperm around it that has already been conquered by the winning sperm and, therefore, that the doors of his kingdom are closed.
Once the sperm enters the oocyte, the nuclei of both are fused. This is what we know as fertilization. If you want to know how the sperm enters the egg and how the new being is formed, you can consult this link: How does fertilization occur?
Questions from users
How much does sperm live in the female reproductive system?
Once ejaculation occurs, and the sperm are released into the vagina, they have a half-life of between 2 and five days. The strongest will survive the longest. The weakest will die on the road. After fertilization, dead sperm and living sperm that has been unable to fertilize the ovum will be eliminated by phagocytosis (system of neutralization and elimination of substances from the body).
How long does the sperm take to get to the egg?
There is not a certain time because the sperm with better quality, with great ability to overcome obstacles and great movement force, will be able to reach the egg in only half an hour. However, others will need about two days to pass through the entire female reproductive system.
Where does sperm pass on their way to the egg?
As we have said, first of all, they have to go through the male reproductive system and, later, after ejaculation, the female reproductive system. In the first part of the path, they exit the testicle and pass through the epididymis, the vas deferens, and the urethra. During this part, they become impregnated with the secretions of the prostate and the seminal vesicle.
In the second part of the route, the sperm passes from the vagina, deposited, to the cervix or cervix. Subsequently, they cross the uterus and reach the fallopian tubes, where the egg is located or where they wait for it to arrive, in case ovulation has not yet occurred.
How far does the sperm get to get pregnant?
The sperm must reach the fallopian tubes, which is where the egg is located. Once there, you can merge with it and give rise to the embryo. Afterward, it will leave the fallopian tubes, reach the uterus, and implant the uterine cavity’s endometrium. This establishes the beginning of pregnancy.
The ultimate goal of all this sperm travel is to meet the ovum, merge with it, and allow a new cell’s birth. This, after about nine months of successive divisions and processes of differentiation and specialization, will lead to the future baby. In these articles, we tell you not only how fertilization occurs but also the different stages of embryo development, created by the fusion of the ovule and sperm:
- Natural pollination
- Embryonic and fetal development throughout pregnancy