394
SECTION IV
Endocrine & Reproductive Physiology
EMBRYOLOGY OF THE HUMAN
REPRODUCTIVE SYSTEM
Development of the Gonads
On each side of the embryo, a primitive gonad arises from the
genital ridge, a condensation of tissue near the adrenal gland.
The gonad develops a
cortex
and a
medulla.
Until the sixth
week of development, these structures are identical in both sex-
es. In genetic males, the medulla develops during the seventh
and eighth weeks into a testis, and the cortex regresses. Leydig
and Sertoli cells appear, and testosterone and MIS are secreted.
In genetic females, the cortex develops into an ovary and the
medulla regresses. The embryonic ovary does not secrete hor-
mones. Hormonal treatment of the mother has no effect on go-
nadal (as opposed to ductal and genital) differentiation in
humans, although it does in some experimental animals.Embryology of the Genitalia
The embryology of the gonads is summarized in Figures 25–4
and 25–5. In the seventh week of gestation, the embryo hasFIGURE 25–4
Embryonic differentiation of male and female internal genitalia (genital ducts) from wolffian (male) and müllerian
(female) primordia.
(After Corning HK, Wilkins L. Redrawn and reproduced with permission from
Williams Textbook of Endocrinology,
7th ed. Wilson JD, Foster DW [editors].
Saunders,1985.)
GubernaculumTestisHydatidVaginal rudimentUrethraProstateSeminal
vesicleVas
deferensEpididymisMALEFimbriaGonadGonadal ligamentMullerian ligament:Uterovaginal
canalBladderMesonephrosWolffian ductUrogenital sinusINDIFFERENTEpoophoron
OvaryUterine tubeOvarian ligamentUterusGartner’s ductFEMALE