- Genital system (gonads, ducts, external genitalia) develops from intermediate mesoderm, cloaca and celomic epithelium, from the 4th week; sexually indifferent till the 7th to 12th week.
Development of Gonads
- Gonad passes through an indifferent stage (invaded by migrating primordial germ cells) before the SRY gene commits it to testis, or, in its absence, ovary.
Testis versus ovary development
Point
Sex cords
- Testis
- One generation (medullary cords) extends into the medulla
- Ovary
- Two generations: medullary cords (regress) and cortical cords (form follicles)
Fate of sex cords
- Testis
- Canalize into seminiferous tubules and rete testis
- Ovary
- Medullary cords form rete ovarii, then disappear, replaced by vascular stroma
Separating layer
- Testis
- Tunica albuginea separates tubules from surface epithelium
- Ovary
- No tunica albuginea; follicles stay continuous with surface epithelium
Germ cell derivative
- Testis
- Spermatogonia
- Ovary
- Oogonia
Sex cord cell derivative
- Testis
- Sertoli cells (sustentacular)
- Ovary
- Follicular cells
Suspending mesentery
- Testis
- Mesorchium
- Ovary
- Mesovarium