May 20, 2018
At the beginning of the monthly cycle, each time anew on a hormonal signal in one of the woman's ovaries, a new egg in the follicle begins to ripen. As is known, during the menstrual cycle in the ovary usually only one follicle ripens, from which approximately on the 14th day of the cycle an egg is ready for fertilization. The remaining follicles, located right next to, next door, are waiting their turn. In the middle of the cycle, the follicle bursts and the mature egg goes out, ovulation occurs.
During this period, the funnel of the fallopian tube expands and begins to oscillate in close proximity to the ovary. The inner part of the pipe begins to rhythmically contract, ready to grab a mature egg and transmit it to meet the spermatozoa. In other words, the fallopian tube works like a real "vacuum cleaner", trying to get a ready-to-fertilize egg.
Pregnancy occurs as a result of penetration of the nucleus of the sperm into the egg. In order for this to happen, the spermatozoon must get into the vagina at a time close to ovulation. Once in the genital tract of a woman, the spermatozoon retains the ability to fertilize for 24-72 hours( that is, up to three days).If a young couple does not use contraceptives and maintains a regular sexual life, pregnancy does not occur immediately, on average, it takes 5.3 months. According to the results of the survey, 5 000 couples, more than 50% of women became pregnant within the first 3 months after the beginning of regular sexual activity, 15% - in 4-6 months, 13% - it took from 7 months to a year, 8% it took from one to two yearsyears, 6% - more than two years. The probability of pregnancy in each monthly cycle, provided a regular sexual life is an average of 20%.
After being ejaculated in the vagina, the spermatozoa quickly move towards the egg. They have to swim a distance of about 15 cm. However, on this long and difficult path, only a few of them will approach the goal. Of the more than 200 million spermatozoa, only a few thousand get to the fallopian tubes, and about 200 are approaching the ovum. Some spermatozoa-
do not reach the cervix at all, others lose mobility or are damaged along the way, half goes to the wrong side and gets into the uterinea pipe in which at that moment there is no egg. The movement of sperm is assisted by rhythmic contractions of the uterus and fallopian tubes.
Spermatozoa can reach the fertilization site 1 to 5 hours after ejaculation. However, spermatozoa acquire a fertilizing ability not immediately. They mature for this only after 7 hours of being in the birth canal of a woman.
Fertilization( the birth of a new life) usually occurs in the upper part of the fallopian tube. A fertilized egg is called a zygote. After the fertilization of the contraction of the tube and the ciliary movements of the cilia of its mucous membrane help the zygote to move along the fallopian tube to the uterus. Such a journey takes 5-7 days. At this time, the zygote begins to divide, and after hitting the uterus, it is attached to its mucosa( implantation takes place).When the embryo is attached to the wall of the uterus, the process of conception is considered complete.
1. Several spermatozoa penetrate through the protective shells of the ovum, penetrating into the radiant crown, which is formed by a mass of cells connected by mucus.
2. The outer shell of the sperm head is destroyed, and it is attached to the surface of the protective shell of the egg.
3. The fertilizing spermatozoon secretes enzymes that promote its penetration through the transparent zone inside the egg cell.
At this point, the egg forms a dense protein layer, which prevents the penetration of other spermatozoa.
4. The spermatozoon merges with the egg.
5. The nucleus of the spermatozoon penetrates into the egg, and the tail is dropped and remains outside the cell.
Penetration of the spermatozoon into the egg.
The process of fertilization lasts about 24 hours from the moment of contact of the spermatozoon with the egg shell before the connection of the chromosomes of the spermatozoon and the ovum:
Development of the embryo from the zygote to the embryo:
1. 30 hours after fertilization, the unicellular zygote becomes a two-celled zygote, and in 3 days it consists of16 cells.
2. After three to four days, the dividing cells form a small ball, called a morula. It moves from the fallopian tube to the uterine cavity.
3. After 5 days, the morula turns into a hollow sphere - a fluid-filled sphere( blastocyst).
4. Approximately one week after fertilization, the blastocyst penetrates the uterine mucosa. From the wall of the uterus, the blastocyst receives oxygen and nutrients. It continues to grow, transforming from this moment into an embryo. Within a month, the embryo becomes 10,000 times larger than the ovule from which it was formed.