Location and Manifestations of Infection
Chapter 22 - The Female Genital Tract
Christopher P. Crum MD
The embryology of the female genital tract is relevant to both anomalies in this region and the histogenesis of various tumors. The primordial germ cells arise in the wall of the yolk sac by
the fourth week of gestation; by the fifth or sixth week, they migrate into the urogenital ridge. The mesodermal epithelium of the urogenital ridge then proliferates, eventually to produce
the epithelium and stroma of the gonad. The dividing germ cells—of endodermal origin—are incorporated into these proliferating epithelial cells to form the ovary. Failure of germ cells
to develop may result in either absence of ovaries or premature ovarian failure. Disruption of normal migration may account for extragonadal distribution of germ cell midline structures
(retroperitoneum, mediastinum, and even pineal gland) and may rarely lead to tumors in these sites.
A second component of female genital development is the müllerian duct. At about the sixth week, invagination and subsequent fusion of the coelomic lining epithelium form the lateral
müllerian (or paramesonephric) ducts. Müllerian ducts progressively grow caudally to enter the pelvis, where they swing medially to fuse with the urogenital sinus at the müllerian tubercle
( Fig. 22-1A ). Further caudal growth brings these fused ducts into contact with the urogenital sinus, formed when the cloaca is subdivided by the urorectal septum. The urogenital sinus
eventually becomes the vestibule of the external genitalia ( Fig. 22-1B ). Normally, the unfused portions mature into the fallopian tubes, the fused caudal portion developing into the uterus
and upper vagina and the urogenital sinus forming the lower vagina and vestibule ( Fig. 22-1C ). Consequently, the entire lining of the uterus and tubes as well as the ovarian surface is
ultimately derived from coelomic epithelium (mesothelium). This close embryologic relationship between the mesothelium and müllerian system may be reflected in adult life in the form
of benign (endometriosis) and malignant (endometrioid and serous neoplasia) lesions, which may arise in both the surface mesothelium of the ovaries and the peritoneal surfaces.
The epithelium of the vagina, cervix, and urinary tract is formed by induction of basal cells from the underlying stroma, which undergo squamous and urothelial differentiation. A
portion of these cells remains uncommitted, forming the reserve cells of the cervix. The latter are capable of both squamous and columnar cell differentiation.
In males, müllerian inhibitory substance from the developing testis causes regression of the müllerian ducts, and the paired wolffian (or mesonephric) ducts form the epididymis and the
vas deferens. Normally, the mesonephric duct regresses in the female, but remnants may persist into adult life as epithelial inclusions adjacent to the ovaries, tubes, and uterus. In the cervix
and vagina, these rests may be cystic and are termed Gartner duct cysts. Many of the events in the
Figure 22-1Embryology and anatomy of the female genital tract. A, Early in development the mesonephric (red) and müllerian (blue) ducts merge at the urogenital sinus to form the
müllerian tubercle. B, By birth the müllerian ducts have fused to form the fallopian tubes, uterus and endocervix (blue) merging with the vaginal squamous mucosa. The mesonephric ducts
regress but may be found as a remnant in the ovary, adnexa and cervix (Gartner duct). (Adapted from Langman J: Medical Embryology. Baltimore, Williams and Wilkins, 1981.) C, Normal
adult genital tract, with cervix, uterus, fallopian tubes, and ovaries. A small paratubal cyst is present on the right.
Figure 22-2Schematic of the development of the cervical transformation zone.
Figure 22-3 A, Colposcopic view of the cervix in a reproductive age woman. The portio epithelium (peripheral) merges with (at dotted boundary) and eventually replaces the endocervical
columnar epithelium (red and grapelike) to form the transformation zone. The os is in the center. B, The postmenopausal cervix. The epithelial surface is smooth and completely covered by
squamous epithelium. The squamocolumnar junction is not visible and is inside the endocervical canal. (A and B, courtesy of Dr. Alex Ferenczy, McGill University, Montreal, Quebec.)
TABLE 22-1-- Anatomic Distribution of Common Female Genital Infections
Location and Manifestations of Infection
Date: 2016-04-22; view: 495