Pregnancy occurs as a result of fertilization-the fusion of Mature male (sperm) and female (egg) germ cells. The maturation of male and female germ cells is complex multistage process. Spermatogenesis occurs in the convoluted seminal tubules of the male gonads. By the time of puberty, Mature spermatozoa are formed, capable of fertilization. Full maturation is preceded by reductive division, as a result, the sperm nucleus contains a haploid set of chromosomes. The sex of the unborn child depends on the carrier of which sex chromosome it is the sperm that fertilized the egg. The egg is always contains the X chromosome. Fusion with an egg of a sperm containing The x chromosome gives rise to a female embryo. During fertilization a sperm with a Y-chromosome produces a male embryo. During sexual intercourse the woman's vagina pouring out an average of about 3-5 ml of sperm, which contains 300-500 million spermatozoa. Part of the sperm, including defective ones, remains in the vagina and undergoes phagocytosis. This is largely facilitated by the acidic environment of the vagina, which is unfavorable for the vital activity of spermatozoa. Together with spermatozoa, other components enter the vagina part of the semen. A special role belongs to prostaglandins. Under their influence the contractile activity of the uterus and fallopian tubes increases, which is very important for the normal transport of gametes. From the vagina, spermatozoa that have retained the ability to fertilize enter the cervical mucus, which is released from the cervical canal during sexual intercourse. Weakly alkaline reaction of the cervical mucus increases the motor activity of spermatozoa.Spermatozoa move along the mucus mycelium towards the uterus. Turbulent movements of spermatozoa are most pronounced in the parietal areas of the cervix. Part of the sperm may be deposited in the crypts of the cervix for some time, creating a kind of reserve. In the upper parts of the female genital tract begins sperm capacitation - the glycoprotein layer and cytoplasmic proteins are removed from the sperm head. In addition, capacitation is expressed in changes in the movements of the tail parts of spermatozoa (overactive mobility). Capacitated spermatozoa acquire an increased ability to penetrate tissue, which is crucial for fertilization eggs. Transport of spermatozoa to the uterus, and then to the fallopian tubes. it is a complex multi-component process. It is provided by contractions of the smooth muscles of the uterus and fluid flow in the lumen fallopian tubes that are under complex hormonal pressure exposure to estrogens, androgens, oxytocin, prostaglandins. Of great importance in the transport of spermatozoa is their own high motor activity. In favorable conditions (with a high content of estrogens in the body
women) the fertilizing ability of spermatozoa in the cervical mucus is preserved up to 2 days after ejaculation in the vagina. The development of eggs (oogenesis) is associated with the growth and development of primaryfollicles located in the cortical layer of the ovaries. In each menstrual cycle, a woman usually Matures one egg. At the time of ovulation, a Mature egg consists of a nucleus, cytoplasm, surrounded by a shiny shell (zona pellucida) and cells the corona radiata, which is a remnant of the corona radiata granulose cells of the follicle. The female sex cell, as well as the male, it has antigenic properties. Especially rich in various antigens its shiny shell. After the rupture of the follicle (ovulation), the egg enters the cavity fallopian tube. This is facilitated by its 'capture' by fimbriae of the fallopian tube tubes on the side of the ovary where ovulation occurred, current direction follicular fluid when the follicle breaks. This factor it has a very important role in the initial transport of the egg, which is devoid of independent mobility. The transport of the egg to the uterus through the fallopian tube is under exposure to progesterone and estrogens-hormones of the yellow body (new endocrine gland formed on the site of a burst follicle). By relatively low levels of progesterone and higher the concentration of estrogens (immediately after ovulation) increases tone of the ampullary-isthmus section of the tube. The result is an egg it is delayed in the ampullary section, where it is surrounded by a large number of spermatozoa, which begin to penetrate into the cells of the radiant crown. The penetration process is caused by enzymes that are contained in both the head of the sperm, and in the tube fluid. The ability of an egg to fertilize is preserved for an average of 24 hours. Fertilization occurs in the ampullary part of the fallopian tube. After the fusion of the sperm and egg, a zygote occurs. The nucleus of a fertilized egg (zygote) contains a diploid set of chromosomes (46). Thus, the new organism becomes a carrier of genetic information. information from both parents. Immediately after the egg merges with one of the Zona p spermatozoa impervious to other spermatozoa. Preimplantation period begins from the moment of fertilization egg cells and continues until the introduction of the blastocyst in the decidual lining of the uterus (5-6 days after fertilization). During during this period the fertilized egg passes sequentially morula and blastocyst stages. After fertilization (after 24 hours), the fertilized egg begins to split mitotic divisions, which result in an increase in the number of cells. Preimplantation embryo blastomeres have the following characteristics high regenerative capacity. This means that when damaged, the separated cells completely restore the function of the lost ones. Environmental factors influence
the embryo during this period of development either transfers the effects, or dies if most of the blastomeres were damaged regeneration is impossible. 4 days after fertilization, the zygote enters the uterus at the morula stage. Implantation of a fetal egg. As soon as the morula enters the uterus, it a cavity appears and a blastocyst is formed (2nd week of intrauterine development) At the blastocyst stage, blastomeres are subjected to certain changes. The larger blastomeres form the embryoblast, from which in the future, the embryo develops. Some of the smaller ones on the periphery of the fetal egg, blastomeres form a nutrient shell-a trophoblast. In the uterine cavity, the blastocyst is approaching the place of implantation (nidation), which is largely determined by local characteristics endometrium. At this point the endometrium becomes decidual a shell that provides the conditions necessary for life embryo's. By the time of implantation, the uterine mucosa is in the secretory phase: the glands are filled with secret, the stroma cells contain a large amount of glycogen, lipids, neutral mucopolysaccharides, salts and trace elements, enzymes and their inhibitors, immunoglobulins and other biologically active compounds. The implantation process, which on average lasts about 2 days, in addition to significant changes in the glands and stroma of the endometrium, it is accompanied by pronounced local hemodynamic shifts. At the site of implantation of the blastocyst, there is an expansion of blood vessels blood vessels and the formation of sinusoids, which are expanded capillaries and venules-a 'window of implantation' is formed (6-7 days after ovulations).