Pregnancy is a natural, natural process. There is an opinion that there are no two identical pregnancies, even for the same woman. The course of pregnancies may be different, but they all always start and they all start the same.
Instructions
Step 1
Any pregnancy begins with the maturation of reproductive cells: in women, eggs ripen cyclically, in men, sperm cells are constantly ripening. These processes are called ovogenesis and spermatogenesis, respectively. A feature of sex cells (gametes) is the presence in their nucleus of a half set of chromosomes, which leads to the fact that when two such cells merge, a zygote is formed with the usual set of chromosomes (46 chromosomes).
Step 2
After the maturation of the germ cells, conditions are necessary for the meeting of male and female gametes, that is, conception. Such conditions are directly sexual intercourse, the apogee of which will be male ejaculation. After that, male gametes, equipped with special tails, make their way along the woman's genital tract to the egg, which is waiting for sperm in one of the two fallopian tubes.
Step 3
After the fusion of the egg and one sperm, the sex of the unborn child is determined: it depends on the presence of a chromosome in the sperm that is responsible for sex. If a zygote with a set of XX chromosomes is formed during the fusion, a girl will be born, and if XY - a boy. In this case, the eggs always carry only X chromosomes.
Step 4
Further, the egg cell begins to divide (the process of cleavage or the formation of multicellularity), a blastocyst is formed, which slowly descends along the fallopian tube into the uterus and attaches itself to the wall of the uterus on the seventh to tenth day (implantation). This period is called the pre-payment period. At the same time, the uterus is also preparing to receive a fertilized egg: all the time that the gamete ripens in the female body, a special lining is growing on the walls of the uterus - the endometrium, which is an ideal substrate to provide the newly formed organism with everything it needs.
Step 5
Pregnancy is conventionally divided into three stages - trimester. In the first trimester, which lasts 12 weeks (embryonic period), there is an intensive formation and laying of all future organs and parts of the fetus's body (organogenesis), and a new organ is formed in the mother's body - the placenta (child's place), which will nourish and protect pregnancy, existing until the moment the fetus is expelled from the womb (placentation).
Step 6
The resulting embryo does not resemble a baby in appearance, only gradually, by the beginning of the fetal period (from the beginning of the 11th week), it will acquire features similar to a newborn. In the meantime, the embryonic period lasts, the embryo will have gill arches, tail, gill slits, allantois.
