In Сhordates and human the ovum is a large (approximately 100 microns) cell, unable (unlike to spermatozoid) to move by itself. It contains a lot of

Oogenesis

In Сhordates and human the ovum is a large (approximately 100 microns) cell, unable (unlike to spermatozoid) to move by itself. It contains a lot of nutrients reserves (protein, fat, carbohydrates), essential for the development of the embryo. The process of formation and ripening of the egg is called oogenesis (from the Latin “egg”).

The ovum matures in the ovaries, and this process in a woman's body begins even before birth. During embryo ripening primary sex cells divide by mitosis, forming a lot of cells, called oogonia. They also divide and form oocytes of the first order. At this stage of development they are from girl’s birth until her puberty. Then begins the next stage of oocytes maturation that is accompanied by meiotic division.

When divided first, becomes uneven division of the cytoplasm, resulting the formation from the oocytes of the first order a large cell — oocyte of the second order and the small cell, which is called the first polar body. After the second meiotic division forms a mature egg with a haploid set of chromosomes capable of fertilization, and the second polar body. Polar body does not play any role in oogenesis and destroys soon. Oogenesis ends after the release of the ovum from antral follicle.

The ovum, released from the ovary, enters the uterus via fallopian tubes. These are the tubes that have mucosal muscle layer with length of 9-11 cm. They are arranged by one on either side of the uterus. Taken from http://worldofschool.org

Diagram 112. Scheme of the ovum (oogenesis)
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Questions:
  • Explain the biological mechanism of oogenesis.