Disorders of Embryonic Sexual Development

Hermaphroditism is a condition in which both ovarian and testicular tissue is present in the body. About 34% of hermaphrodites have an ovary on one side and a testis on the other. About 20% have ovotestes—part testis and part ovary— on both sides. The remaining 46% have an ovotestis on one side and an ovary or testis on the other. This condition is extremely rare and appears to be caused by the fact that some embryonic cells receive the short arm of the Y chromosome, with its SRY gene, whereas others do not. More common (though still rare) disorders of sex determination involve individuals with either testes or ovaries, but not both, who have accessory sex organs and external genitalia that are incompletely developed or that are inappropriate for their chromosomal sex. These individuals are called pseudohermaphrodites (pseudo = false).

The most common cause of female pseudohermaphroditism is congenital adrenal hyperplasia. This condition, which is inherited as a recessive trait, is caused by the excessive secretion of androgens from the adrenal cortex. Because the cortex does not secrete mullerian inhibition factor, a female with this condition would have mullerian duct derivatives (uterus and fallopian tubes), but she would also have wolffian duct derivatives and partially masculinized external genitalia.

Table 20.1 A Developmental Timetable for the Reproductive System

Approximate Time After Fertilization Developmental Changes

Days

Trimester

Indifferent

Male

Female

19

First

Germ cells migrate from yolk sac.

25-30

Wolffian ducts begin development.

44-48

Mullerian ducts begin development.

50-52

Urogenital sinus and tubercle develop.

53-60

Tubules and Sertoli cells appear.

Mullerian ducts begin to regress.

60-75

Leydig cells appear and begin

Formation of vagina begins.

testosterone production.

Wolffian ducts grow.

Regression of wolffian ducts begins.

105 120 160-260

Second Third

Testes descend into scrotum. Growth of external genitalia occurs.

Development of ovarian follicles begins.

Uterus is formed.

Formation of vagina is complete.

Source: Reproduced, with permission, from the Annual Review of Physiology, Volume 40, p. 279. Copyright © 1978 by Annual Reviews, Inc.

Source: Reproduced, with permission, from the Annual Review of Physiology, Volume 40, p. 279. Copyright © 1978 by Annual Reviews, Inc.

An interesting cause of male pseudohermaphroditism is testicular feminization syndrome. Individuals with this condition have normally functioning testes but lack receptors for testosterone. Thus, although large amounts of testosterone are secreted, the embryonic tissues cannot respond to this hormone. Female genitalia therefore develop, but the vagina ends blindly (a uterus and fallopian tubes do not develop because of the secretion of mullerian inhibition factor). Male accessory sex organs likewise cannot develop because the wolffian ducts lack testosterone receptors. A child with this condition appears externally to be a normal prepubertal girl, but she has testes in her body cavity and no accessory sex organs. These testes secrete an exceedingly large amount of testosterone at puberty because of the absence of negative feedback inhibition. This abnormally large amount of testosterone is converted by the liver and adipose tissue into estrogens. As a result, the person with testicular feminization syndrome develops into a female with well-developed breasts who never menstruates (and who, of course, can never become pregnant).

Some male pseudohermaphrodites have normally functioning testes and normal testosterone receptors, but they genetically lack the ability to produce the enzyme 5a-reductase. Individuals with 5a-reductase deficiency have normal epididymides, ductus (vasa) deferentia, seminal vesicles, and ejacu-latory ducts because the development of these structures is stimulated directly by testosterone. The external genitalia are poorly developed and more female in appearance, however, because DHT, which cannot be produced from testosterone in the absence of 5a-reductase, is required for the development of male external genitalia.

Chapter Twenty

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Bacterial Vaginosis Facts

Bacterial Vaginosis Facts

This fact sheet is designed to provide you with information on Bacterial Vaginosis. Bacterial vaginosis is an abnormal vaginal condition that is characterized by vaginal discharge and results from an overgrowth of atypical bacteria in the vagina.

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