Normal sexual differentiation
Endocrinology / / May 02, 2016
Congenital disorders of sexual differentiation
Formation genitalia is determined by genetic, gonadal and hormonal factors, and normal differentiation of them completed by the end of 12 weeks of pregnancy.
embryo is formed at the confluence of the egg and sperm, with half (haploid) set of chromosomes.In addition to 22 autosomes, germ cell contains one sex chromosome - the egg always contains a fairly large X-chromosome, and sperm - or the X chromosome or a small Y -hromosomu.At the confluence of germ cell nuclei arises a set of 22 pairs of autosomes and two sex chromosomes.If the two X-chromosome set occurs XX, giving rise to the female, in the presence of X and Y -hromosom - XY set giving rise to the male.
Chromosomal abnormalities can occur at different stages.During cell division, the embryo of a number of chromosomes are evenly distributed between daughter cells, resulting in a haploid set will contain more than one sex chromosome, and two or none.Sex chromosomes may fall at fertilization.Finally
germ cell has only the X chromosome, gonadal development occurs in the female side, if in the cell there -hromosoma Y, then - in a man, but it requires a set of normal chromosomes for normal gonadal development and the absence of one of them, or the presence ofextra chromosomes will almost always lead to disease.After two weeks, all of the X chromosome in embryo nuclei, but one biologically inactivated and, lying on the periphery of the nucleus, strongly stained nuclear paints.Such a body size of about 1 micron, called sex chromatin is usually determined in the cells of the epithelium of the mucous membrane of the cheeks, or in the form of "clubbing" in the nuclei of segmented neutrophils, it normally has for women and no men.
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at 5-6 weeks of development in the lumbar region of the embryo begins the formation of the gonads, and there gonocytes (future germ cells) migrate to that time.The gonads are derived from coelomic epithelium (cortex) and mezonefriticheskih elements (medulla).If germ cells contain -hromosomu Y, then the development goes towards the medulla, are formed in the seminiferous tubules, and the elements of mezhkanaltsevyh - leydigovskie cells.In the absence of X -hromosomy superiority gets the cortical layer forming follicles.On the 7th week of development in the bud laid Wolffian and Müllerian ducts, of which later formed the internal reproductive organs.Embryonic egg produces two non-steroidal hormones - one of them is the development of the Wolffian ducts (of which there are the epididymis, vas deferens and seminal vesicles);other causes atrophy of Müllerian derivatives.In the absence of the testes (in females or in the absence of gonads) Wolffian duct atrophy, and Mullerian develop and form the uterus, tubes and the upper part of the vagina.These processes are completed in the third month of development.At that time, formed the external genitalia that in embryos of either sex are laid in the form of the urogenital sinus and genital tubercle, which are located posterior urethral scrotal folds and ridges.If the embryo has enough androgens (normally formed egg, and in pathology and the adrenal cortex, or falling out of the mother's body), then sexual tubercle forms the penis and fused folds - the scrotum.If the number is low androgen (or more precisely - the threshold is not known), then sexual mound preserved in the form of the clitoris, the urethral folds to form small, and scrotal - the labia majora, of the urogenital sinus forms the lower part of the vagina.After completion of the formation of the genitalia excess of androgens in the female fetus can lead to hypertrophy of the clitoris, but not to other violations of genital structure.
Psychosexual direction is formed by the age of 2 years and depends on the social environment and education.Decisive in this case is then considered whether the child is a boy or girl, depending on the sex of the diagnosis established at birth on the basis of the type of the external genitalia.If the view of the external genitalia uncertain, the child grows up with a psycho-sexual orientation, which corresponds to his passport floor.In view of the sex of the child must always be clearly established no later than two years of life.