Genital System

Question 1

When is the genotype of the embryo (46,XX or 46,XY) established?

When do embryos begin phenotypic sexual differentiation?

Answer 1

• at fertilization
• week 7

(week 1-6 male/femal embryos are sexually indifferent)

Question 2

Week 7: What 3 sources are developing gonades derived from?

Answer 2

• Mesothelium (lining posterior abdominal wall)
• Underlying mesenchyme (embryonic connective tissue)
• Primordial germ cells

Question 3

indifferent stage of sexual development:

Answer 3

Week 5:

- mesothelium thickens in an area on medial side of mesonephros

• proliferation produces gonadal ridge
• gonadal cords (fingerlike epithelial cords) grow into underlying mesenchyme

Week 6:

• (primordial germ cells, from embryo part of umbilical vesicle, migrate along dorsal mesentery of hindgut to gonadal ridges)*
• cells enter underlying mesenchyme + incorporate into the gonadal cords

Question 4

How are the phenotyps determined for indifferent gonads (gonades before wk7) ?

Answer 4

• male phenotype = determined by SRY gene for testis- determining factor (TDF) (present in Y chromosome)
• gonadal cords differentiate into seminiferous cords due to TDF influence
• female phenotype = requires two X chromosomes.

Question 5

What is required for the normal determinaltion of female and male sexual differentiation?

Answer 5

normal male sexual differentiation:

• Testosterone (from fetal testes)
• dihydrotestosterone
• antimullerian hormone (AMH)*

*(produced by Sertoli cells; suppresses dvlpmt. of paramesonephric ducts)

Primary female sexual differentiation:

• does not depend on hormones
• occurs even if ovaries are absent

Question 6

Development of the Testes:

(begins @ week 7)

Answer 6

• TDF induces gonadal cords to condense + extend into medulla of indifferent gonad; lose their connection w surface epithelium as thick tunica albuginea forms

- cords branch + anastomose to form rete testis; continuous w 15- 20 mesonephric tubules (efferent ductules) = connected w mesonephric duct ==> duct of the epididimys

• seminiferous tubules separated by mesenchyme; gives rise to Leydig cells (interstitial); tubules = no lumen until puberty; walls contain Sertoli cells + spermotagonia
• By week 8: Leydig cells secrete androgenic hormones:
• Testosterone*
• Androstenodione*

(induce masculine differentiation of mesonephric ducts + external genitalia)

Question 7

What are the “male” and “female” ducts that develop from the mesonephric duct?

The presence of what hormones suppresses development of the “female” duct?

Answer 7

present @ week 5 - 6:

MALE = Wolffian Duct (mesonephric)

FEMALE = Mullerian Duct (paramesonephric)

• presence of high levels of AMH (antimullerian hormone) + Testosterone suppress development of the Mullerian Duct

Question 8

Development of the Ovaries:

Answer 8

- Week 10: gonadal cords appear + extend into medulla = rudimentary rete ovarii (normally degenerate+disappear)

• Cortical cords extend from surface epithelium of developing ovary into mesenchyme

- Week 16: cortical cords break up into isolated cell clusters - primordial follicles*

*(oogonia surrounded by single layer of follicular cells)

SIDE NOTE:

• funnel shaped cranial ends of paramesonephric ducts open into peritoneal cavity (primordium of fimbrae?)

Caudally = parallel to mesonephric ducts until pelvis; fuse to form Y- shaped uterovaginal primordium

Question 9

Approximate number of Oocytes:

(Primary vs. Secondary)

Answer 9

**Primary oocytes: **

**- **month 5 of fetal life = 7 million primary

• At birth = 2 million
• At puberty = 40,000

Secondary oocytes:

12 ovulated per year (up to 480* over the entire reproductive life)

*reduced in women who take birth control pills, women who become pregnant, women with anovulatory cycles