The prenatal period of development

Female sexual organs are formed on the 5th week of intrauterine period of development when the length of an embryo 9-10 mm [Petrova E. I., 1959; Volkova O. V. and others, 1976]. Differentiation of the gonads to the testes and ovaries begin with the 7th week of fetal life. The decisive factor in sexual differentiation are the sex chromosomes. Sex of the fetus is determined by the set of chromosomes of a fertilized egg. Sex cells unlike all other cells contain half the number of chromosomes. The nuclei of all eggs contain along with 22 autosomes the X chromosome. During fertilization of an egg by a sperm carrying the X chromosome, reproductive cell already contains 44 autosomes and 2 of the sex chromosomes. This combination of fertilized eggs develop a girl. If chromosomes typical female phenotype and the pregnancy is physiologically, born girls will normally formed genitals.
The development of the ovaries as sexual glands begins from the 10th week of fetal life. Thus there is degeneration of primary genital cords and new layers of coelomic epithelium grow into mesenchyme. Prisoners in them geocity are enhanced division. Due to the growing cells mesenchyme in mullerova the fibres, they are divided into groups of cells, and this process continues until each egg is separated from the next by a layer of epithelial cells, i.e. formed the primary (primordial) follicles. In the absence of the influence of excess androgens genitals are differentiated by female type.
In the period of intrauterine development ovaries do not have hormonal activity, although by the end of the formation of ovarian almost over and they acquire the ability to secrete estrogen [Kobozev N. Century, 1970]. However, the amount of estrogen secreted so low that their influence is not manifested until then, until the body and the sexual system will not be able to perceive the influence of sexual hormones.
During fetal development, the fetus is under the influence of hormones from the mother's body. In this connection within 1-2 weeks after the birth of girls is often observed bloating mammary glands that is a clinical symptom of the influence of sex hormones mother. In addition, in the vaginal swabs newborn find orogovevshie cells, which quickly disappear, and in subsequent PAP test consists of atrophic cells.
Differentiation of the hypothalamus is postnatala, after years of a child's life. In sexual dimorphism in utero participate not the gonadotropins, and testicular hormones which influence preobrazheskaya area of the hypothalamus is becoming refractory. Thus, gender differences, provide different levels of secretion of the gonadotropins in ontogenesis, not associated with dimorfismo pituitary cells, as defined at the beginning testicular hormones.
The gonadotropins from the pituitary gland of fruit appear in the early stages of its development - from the 8th week, the level reaches its maximum on 21-22 weeks and then declines after the 30th week [Kuznecova M. N., 1980]. It is important to emphasize that in the embryonic period, as well as after birth to puberty, the pituitary gland is functioning toniceski, and only with the onset of puberty begins cyclic secretion of the gonadotropins, which continues throughout the reproductive period.