Development of the Genital System

Question 1

When does sexual differentiation begin?

Answer 1

week 7

Question 2

When can genitalia be recognized in utero?

Answer 2

week 12

Question 3

When is phenotypic differentiation complete in utero?

Answer 3

week 20

Question 4

How do primordial germ cells develop through week 5?

Answer 4

specified w/in epiblast –> end up in yolk sac wall after gastrulation and body folding –> migrate up dorsal mesentery to enter genital ridge at week 5

Question 5

What occurs to gonads at week 6?

Answer 5

primordial germ cells migrating to genital ridge

somatic support cells start dividing

Question 6

What do the somatic support cells develop into?

Answer 6

male –> sertoli cells

female –> follicle cells

Question 7

What does the mesonephric duct differentiate into?

Answer 7

(male stuff)

epididymis

vas deferens

seminal vesicle

ejaculatory duct

Question 8

What do the paramesonephric/mullerian ducts differentiate into?

Answer 8

(female stuff)

oviduct

uterus

upper vagina

Question 9

What do both the mesonephric and paramesonephric ducts arise from?

Answer 9

intermediate mesoderm of the urogenital ridge

Question 10

What is the SRY gene?

Answer 10

on Y chromosome

expressed in somatic support cells –> upregulates testis-specific genes

sertoli cells organize seminiferous tubules

make paramesonephric ducts degenerate

Question 11

When is SRY gene active?

Answer 11

days 41-52

Question 12

What do fetal leydig cells arise from?

Answer 12

sertoli cells recruit intertubular cells –> fetal leydig

Question 13

What specific genes does SRY turn on?

Answer 13

SRY –> Sox9 –> Anti-Mullerian Hormone (AMH)

Question 14

In a male, when do the mullerian ducts degenerate?

Answer 14

weeks 8-10

Question 15

What are the remnants of the mullerian duct in males?

Answer 15

appendix testis

prostatic utricle

Question 16

What do adult leydig cells do?

Answer 16

produce androgens –> initiate spermatogenesis

masculinize brain

Question 17

What does 5 alpha reductase do?

Answer 17

converts testosterone –> dihydrotestosterone

Question 18

What does the seminal vesicle arise from?

Answer 18

buds off of mesonephric duct = intermediate mesoderm of urogenital ridge

Question 19

What do the prostate and bulbouretral glands arise from?

Answer 19

prostate = endoderm of UG sinus week 10

bulbouretral glands from endodermal buds

Question 20

What does the genital tubercle arise from?

Answer 20

ectodermal-covered mesoderm

Question 21

How does the male external genitalia arise?

Answer 21

cloacal membrane ruptures –> phalic portion of urogenital sinus open to exterior –> urogenital plate forms at roof (endoderm)

glans plate = remnants of cloacal membrane at ventral end or urotenital plate (endoderm)

Question 22

How are the urogenital groove and fold related to male external genitalia?

Answer 22

In 7th week perineum made of urogenital groove, w/ urogenital fold lateral (glands plate still present) –> fold eventually elongates and surrounds the groove

Question 23

What does DHT do to the developing penis?

Answer 23

drives lengthening and growth of genital tubercle and fusion of labioscrotal swellings to form scrotum

urethra closed by week 14

Question 24

What is contained in the suspensory ligament of the testes?

Answer 24

gonadal vessels, nerves, lymphatics

Question 25

How do the testes descend?

Answer 25

start at T10 --\> gubernaculum attached to scrotum and pulls them down

Question 26

What is hypospadias?

Answer 26

urethra on ventral side of penis 0.5% of all births

Question 27

What is epispadias?

Answer 27

urethra opens on dorsal side of penis 1:120000 associated w/ exstrophy of bladder body folding issue?

Question 28

What occurs genetically to induce the ovary?

Answer 28

no SRY --\> WNT-4 expressed --\> FOXL2 suppresses SOX9 promotes female genetalia

Question 29

What do oocytes develop from?

Answer 29

primordial germ cells --\> oogonia --\> oocytes

Question 30

What do follicle cells do?

Answer 30

somatic cells --\> follicle cells surround oocytes and block them in meiosis I

Question 31

What happens to the duct system in the developing female?

Answer 31

no sertoli cells --\> no AMH, so paramesonephric/mullerian ducts retained no leydig cells so mesoneprhic duct system is lost

Question 32

How does the uterus form and at what time?

Answer 32

inferior paramesonephric/mullerian ducts fuse weeks 9-10 \*uterine tubes are unfused superior portion of mullerian ducts\*

Question 33

What are the 6 discussed uterus anomalies?

Answer 33

double uterus, double vagina double uterus bicornate uterus septated uterus unicornate uterus cervical atresia

Question 34

How does the vagina form?

Answer 34

sinovaginal bulb fromed from endoderm at 10th week begins to elongate and canalize --\> finished w/ hymen at 20 weeks upper vagina = mesoderm lower vagina = endoderm

Question 35

How does the female external genitalia form?

Answer 35

beginning is same = urogenital plate, glans plate, and genital tubercle no Testosterone --\> no DHT --\> no lengthening of genital tubercle, no fusion of urogenital folds or labioscrotal swellings genital tubercle becomes clitoris

Question 36

How does the broad ligament form?

Answer 36

midline fusion of mullerian ducts --\> lower urogenital ridge within pelvic cavity and is covered w/ peritoneum when uterus and oviducts are finished, remaining tissue thins = double fold of peritoneum supporting uterus and ovary

Question 37

What do the parts of the gubernaculum develop into in the female?

Answer 37

superior part --\> round ligament of ovary (ovary to uterus) inferior part --\> round ligament of uterus (uterus to labia majora)

Question 38

What are disorders of sex development (DSD)?

Answer 38

development of chromosomal, gonadal, and anatomic sex is atypical (1:5000)

Question 39

46, XY DSDs

Answer 39

genotype = male, has testis, but phenotype is female causes: inadequate T synthesis (17 beta dehydrogenase defect) androgen insensitivity 5 alpha reductase deficiency mutations in AMH or AMH receptor

Question 40

Androgen insensitivity syndrome

Answer 40

common cause is loss of functional androgen receptors (X-linked recessive, 1:20000) have testis by no spermatogenesis at puberty, T--\> estradiol --\> female secondary traits form produce AMH, so no uterus or uterine tubes, vagina short and ends blindly increased risk of testicular cancer

Question 41

5 alpha-reductase deficiency

Answer 41

46, XY genotype AR inheritence normal testis and duct system underdeveloped male external genitalia

Question 42

Female DSDs

Answer 42

46, XX genotype have ovaries, but masculine external genitalia most common cause = congenital adrenal hyperplasia

Question 43

Ovotesticular disorders

Answer 43

true intersexuality both testes and ovarian tissue causes: translocation of a piece of Y onto X (barr body causes mosaicism) subset of cells may have Y mutation anomaly in sex determination and differentiation of primordial germ cells

Question 44

What is distinct about GnRH's action on the ant pit?

Answer 44

upregulates its own receptor in the ant pit in add'n to promoting LH and FSH secretion