EMBRYOLOGY

EMBRYOGENESIS

Embryogenesis is part of ontogenesis, it includes time from the moment of fertilization of oocyte by spermatozoon and formation of zygote till the birth.

Embryogenesis is divided into three periods:

1) primary - the first week of development;

2) embryonic - second to eigth weeks of development;

3) fetal - continues from ninth week of intranatal development till the birth of child.

Embryogenesis is closely connected with progenesis. Progenesis is period of development and mature of sexual cells - oocytes and spermatozoa. As a result of progenesis in mature sexual cells haploid number of chromosomes appears, structures providing their ability to fertilization and development of new organism are formed.

Spermatozoa.

Human sperm is formed during the whole active life. Among sperms fifty per cent contain X-chromosomes and fifty per cent - Y-chromosomes. Weight of X-chromosome is more then weight of Y-chromosome, that is why sperms containing X-chromosome are less mobile, then containing Y-chromosome.

In human being volume of ejaculation in norm is about three milliliter. In one ejaculate about three hundred and fifty million spermatozoa are present. For providing fertilization general number of spermatozoa must be about one hundred and fifty million, and concentration of spermatozoa in one milliliter - about sixty million.

Thanks to high mobility spermatozoa can reach cavity of uterus after thirty minutes - one hour; and after one and a half to two hours - in distal (ampular) part of uterine tube, where fertilization occurs. They keep their fertile ability during one to two days.

Oocyte.

Oocyte has a diameter about one hundred and thirty micrometers and is surrounded by dense brilliant zone or membrane and corona of follicular cells. Human oocyte is secondary isolecital type.

It contains a little yolk granules located in ooplasm regularly. Reserve of nutritive substances human oocyte lost during twelve to twenty-four hours after ovulation, then it is dead, if fertilization does not take place.

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