Reproductive System

I. INDIFFERENT EMBRYO. Between weeks 1 and 6, female and male embryos are phe-notypically indistinguishable, even though the genotype (XX or XY) of the embryo is es-tablished at fertilization. By week 12, some female and male characteristics of the external genitalia can be recognized. By week 20, phenotypic differentiation is complete.

A. Phenotypic differentiation is determined by the Sry gene, which is located on the short arm of the Y chromosome.

1. The Sry gene encodes for a protein called testes-determining factor (TDF). TDF is a 220-amino acid nonhistone protein that contains a highly conserved DNA-binding region called a high mobility group box.

2. As the indifferent gonad develops into the testes, Leydig cells and Sertoli cells differentiate to produce testosterone and mullerian-inhibiting factor (MIF), respectively.

3. In the presence of TDF, testosterone, and MIF, the indifferent embryo will be directed to a male phenotype.

4. In the absence of TDF, testosterone, and MIF, the indifferent embryo will be directed to a female phenotype.

B. The components of the indifferent embryo that arc remodeled to form the adult female and male reproductive systems are the gonads, paramesonephric (miillerian) duct, mesonephric (wolffian) duct and tubules, phallus, urethral folds, and genital swellings (Figure 9-1 and Table 9-1).

II. DESCENT OF THE OVARY AND TESTES. The ovaries and testes develop within the abdominal cavity but later descend into the pelvis and scrotum, respectively. This descent involves the gubernaculum (a band of fibrous tissue) and the processus vaginalis (an evagination of peritoneum).

A. Ovary

1. The gubernaculum extends from the ovary to the junction of the uterus and uterine tubes (forming the ovarian ligament in the adult female) and then continues into the labia majora (forming the round ligament of the uterus in the adult female).

2. The processus vaginalis is obliterated in the adult female.

B. Testes

1. The gubernaculum extends from the testes to the genital swellings (forming the gubernaculum testes in rhe adult male, which anchors the testes within the scrotal sac).

A. The Indifferent Embryo

Paramesonephric duct

Paramesonephric duct

Mesonephric Tubule

Mesonephric tubules Mesonephric duct

Uterovaginal primordium Vaginal plate

( Urogenital sinus

Mesonephric tubules Mesonephric duct

Uterovaginal primordium Vaginal plate

( Urogenital sinus

Phallus

Urethral folds

Genital swellings

Phallus

Urethral folds

Genital swellings

B. Female Reproductive System tors/

No factors

C. Male Reproductive System

\TDF, Testosterone, M IF

Hydatid of Epoophoron Morgagni / paroophoron

Appendix vesiculosa

Uterine tubes

Hydatid of Epoophoron Morgagni / paroophoron

Uterine tubes

Virilized Female

Appendix vesiculosa

Inferior two thirds of the vagina

Hymen

Appendix testes

Appendix epididymis

Urinary bladder _ . _ Seminal vesicle

Í-Cervix and superior third of the vagina

Inferior two thirds of the vagina

Hymen

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