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ENDOCRINE PHYSIOLOGY

Gonad and Genital Duet Formation

(pulled aside)

I .‘rogemtoi

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Testosterone from Ihe fetal testes acls locally on the wolffian ducts causing them to persist and differentiate mullerian inhibiting factor, also secreted by the fetal testes causes degeneration of the mullerian ducts

Female

Skenes duet BarthoIin's gland

Ovary Wolffian duet

Uterus Round lig Upper vagina Wolffian duet remnant Urethra

Figurę 8.23 Gonad and Genitał Duct Formation

Based on the expression of spodlić gene products under the control of the sex chromosomem (X and Y chromosomes). the undifferentiated gonads and duct system of the human embryo develop along the małe or female lineage (the exact role of these gene products |SRY and DAXI genesl are still being investigated). In Ihe presence of SRY gene expression (46XY complement of chromosomesthe fetal testes develop and produce testosterone, which acts locally on the mesonephric (wolffian) duct system (shown in red), which persists and develops into the efferent ductules, epididymis, vas deferens, ejacula-tory ducts, and the seminal vestdes. The paramesonephric (mullerian) ducts degenerate in response to a hormone called mullerian-inhibiting substance secreted by the fetal testes. In the absence of testosterone. the gonads of a normal female fetus (4f>XX complement of chromosomes) differentiate into paired ovaries, and the paramesonephric duct system (shown in blue in the left panels) persists while the mesonephric ducts degenerate. The paramesonephric ducts gives rise to paired uterine (tallopian) tubes, a midline uterus, and the upper por tion of the vagina.

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