Conception is the biological process that begins pregnancy. As a result of conception, an embryo appears in a woman's womb, from which a full-fledged, viable human individual will be formed.
In everyday consciousness, conception is often identified with sexual intercourse. Considering that intercourse takes a few minutes, conception is also considered "a matter of minutes." This idea does not correspond to reality: conception is a relatively long process that does not coincide in time with sexual intercourse, the result of which is conception.
Conception includes three stages: fertilization, cleavage and implantation.
Fertilization
The main content of the fertilization stage is the "meeting" of the sperm with the egg. It occurs about 2 hours after the sperm enters the vagina - this is the time the sperm needs to get to that part of the fallopian tube, which is directly adjacent to the ovary, where the mature egg is located.
When the sperm enters the egg, its membrane is destroyed, a zygote appears - a special cell with two pronuclei (nuclei that have a single chromosome set). The process of convergence of pronuclei, ending with their fusion, takes more than a day - 26-30 hours.
Splitting up
The content of the cleavage stage is the division of the zygote and the subsequent division of daughter cells, and each time the daughter cells are smaller than the mother's in size. The cells that form at this stage are called blastomeres.
The crushing stage lasts several days. A "significant event" occurs on the 4th day, when the number of blastomeres reaches 16: cells that have not yet differed from each other differentiate for the first time - some cells form an embryoblast (a prototype of an embryo), while others form the outer layer, which on the 5th day forms a spherical shell. This is how a blastocyte appears, which will develop for several more days.
Implantation
While crushing is going on, the blastocyte does not remain in place: contractions of the fallopian tube gradually move it towards the uterus. It can be said without exaggeration that this path is difficult and dangerous: only one embryo out of ten can survive it! That is why women sometimes experience delays in their periods, which are not followed by pregnancy.
The embryo will reach the uterus on the 11th day after fertilization. Now it must attach to the inner lining of the uterus - the endometrium, this is called implantation. For this to happen, the shell of the embryo must break through, after which it will develop finger-like processes. This process takes about 40 hours.
Thus, the total duration of conception in humans - from the beginning of fertilization to the completion of the embryo's implantation into the uterus - is approximately 12, 5-13 days, almost two weeks.
