Embryology of the Reproductive Tract

Published on 10/03/2015 by admin

Filed under Obstetrics & Gynecology

Last modified 10/03/2015

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Chapter 1 Embryology of the Reproductive Tract

Development of the Ovary 2

Development of Uterus and Fallopian Tubes 5

Development of External Genitalia 7

Development of Male External Genitalia 9

Development of the ovary

The germ cells, which will eventually inhabit the gonads, originate from the primitive hind gut. They appear around the 25th day.

By 30 days, the gut, complete with its mesentery, is formed. The germ cells now migrate from the gut to the root of the mesentery. Of the original 6 or 7 million, only 1–2 million are present at birth and this number is reduced to 300,000 at puberty. A smaller number of these cells may be a factor that leads to premature menopause.

At the same time, the coelomic epithelium proliferates and forms thickenings, the genital ridges, together with the underlying mesenchyme on either side of the mesenteric root, near the developing kidney.

At this stage, the primitive gonad (genital ridge) consists of a mesoderm (coelomic epithelium plus mesenchyme) covered by the coelomic epithelium. The germ cells now migrate from the root of the mesentery to the genital ridge.

The coelomic epithelium, growing into the genital ridge, forms the so-called sex cords, which enclose each germ cell.

Until this time, that is, around the 7th week, the gonad is of an indifferent type, the male being indistinguishable from the female.

The germ cells and most of the sex cord cells remain in the superficial part, which is the future cortex of the ovary. The cords then lose contact with the surface epithelium and form small groups of cells, each with its germ cell, a primitive follicle. Some of the sex cord cells grow into the medulla. These tend to regress and form rudimentary tubules, the rete.

As the ovary grows, it projects increasingly into the peritoneal (coelomic) cavity, thus forming a mesentery.

Simultaneously, the ovary descends extraperitoneally within the abdominal cavity. Two ligaments develop and these may help to control its descent, guiding it to its final position and preventing its complete descent through the inguinal ring, in contrast to the testes. The first structure is the suspensory ligament attached to the anterior (cephalic) pole of the ovary which connects it with its site of origin, the genital ridge.

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