Embryo

Question 1

Where does the indifferent gonad develop from?

Answer 1

Intermediate mesoderm
- along posterior wall of abdominal cavity

Question 2

The primordial germ cells arise from ________________ then migrate ____________ to arrive at __________.

Answer 2

From wall of yolk sac close to allantois

Migrate along dorsal mesentery of hindgut

Arrive @ primitive gonads in wk5

Invade gonadal ridge in wk6

Question 3

Indifferent gonads appear initially as longitudinal gonadal ridges before the epithelium penetrates the mesenchyme to form ______________, which connect to the ___________.

Answer 3

Epithelium penetrate mesenchyme → sex cords → connected to surface epithelium

Question 4

How far in embryological development do male and female characteristic form?

Answer 4

7th week

Question 5

Describe the formation of the testes in an embryo.

Answer 5

1) Under SRY gene influence, primitive sex cords proliferate and penetrate deep into medulla

2) Become horseshoe-shaped in 4th month

3) Cords near testes hilum break up → form network (Rete testes)

Question 6

True or false:
The testes cords are solid throughout childhood/infancy.

Answer 6

True.
At puberty, solid testes cords acquire lumen → seminiferous tubules

Question 7

What is the embryological origin of Sertoli cells?

Answer 7

Gonadal surface epithelium

Question 8

What is the embryological origin of Leydig cells?

Answer 8

Mesenchyme of gonadal ridge

Question 9

Leydig cell develop from ____________ shortly after onset of ___________ but only produce testosterone from _________ onwards.

Answer 9

From mesenchyme of gonadal ridge

shortly after onset of testis cord differentiation

produce testosterone 8th week onwards

Question 10

What do the abdominal structures that are brought down during the descent of the testis form?

Answer 10

1) Processes vaginalis → parietal and visceral tunica vaginalis

2) Transversalis fascia → Internal spermatic fascia

3) Internal oblique muscle → cremasteric fascia and muscle

4) External oblique muscle → external spermatic fascia

Question 11

What are the 4 controlling factors for the descent of the testes?

Answer 11

1) Outgrowth and regression of gubernaculum

2) ↑intra-abdominal pressure due to organ growth

3) Androgens

4) Mullerian inhibiting substances

Question 12

What is a congenital inguinal hernia?

Answer 12

Descent of intestinal loops into scrotum

Question 13

What does an unobliterated processes vaginalis result in?

Answer 13

Communicating hydrocele

Question 14

What are the 2 pairs of indifferent genital ducts?

Answer 14

1) Mesonephric (Wolffian) ducts
2) Paramesonephric (Mullerian) ducts

Question 15

What are 3 factors that influence the development of indifferent genital ducts?

Answer 15

1) Androgens (testosterone, DHT)

2) Oestrogens

3) Anti-mullerian hormone (mullerian inhibiting substance)

Question 16

What are the structures that form the mesonephric duct and how are they formed?

Answer 16

1) Epididymis
- mesonephric ducts elongate and become highly convoluted

2) Ductus deferens
- from tail of epididymis to seminar vesicles
- ducts obtain thick muscular coat

3) Ejaculatory ducts
- from beyond seminar vesicles

Question 17

What are the structures that arise from the cloaca?

Answer 17

1) Urinary bladder
2) Anal canal

Question 18

Describe how the cloacal/urogenital folds develop into the urethral and anal folds.

Answer 18

1) Cranial to caudal membrane unite → genital tubercle

2) Caudally: Cloacal membrane subdivides into urogenital and anal membranes @ wk6 → urethral and anal folds

Question 19

During the development of male external genitalia, the genital swellings are separated by ______________

Answer 19

Scrotal septum

Question 20

Describe the development of the male external genitalia.

Answer 20

Rapid elongation of genital tubercle
→ pull urethral folds forward
→ form urethral groove
- extends along caudal aspect of elongated phallus
- lined by endodermal cells → form urethral plate
- urethral folds close over urethral plate → penile urethra (end of 3rd mth)

Question 21

What is hypospadias?

Answer 21

Opening of penile urethra is located on the underside/along shaft of the penis

• due to incomplete closure of urethral folds over urethral plate

Question 22

Describe the formation of the ovary from indifferent sex cords.

Answer 22

1) Primitive sex cords dissociate into irregular cell clusters → occupy ovary medulla

2) Primitive germ cells replaced by vascular stroma → ovarian medulla

3) Surface epithelium of female gonad proliferates → cortical/secondary cords @ wk7

Question 23

What are the structures that are formed by the cortical/secondary cords in an ovary?

Answer 23

1) Penetrate underlying mesenchyme

2) Split into isolated cell clustered & surround primitive germ cells

3) Germ cells form oogonia

4) Surrounding epithelial cells → follicular cells

Question 24

Where does the paramesonephric/Mullerian ducts that form the main female genital ductal system arise from?

Answer 24

Longitudinal invagination of epithelium on anterolateral surface of urogenital ridge

Question 25

What are the structures that arise from the paramesonephric ducts?

Answer 25

1) Uterine tubes
2) Uterus
3) Upper part of vagina

Question 26

What are the 3 parts of the paramesonephric duct and what do they form?

Answer 26

1) Cranial vertical part
- opens into abdominal cavity w funnel-like structure
- fimbriae

2) Horizontal part
- broad ligament of uterus
- divides pelvic cavity into uterorectal & uterovesical pouches

3) Caudal vertical part
- contact opposite paramesonephric duct in midline
- caudal tip projects into posterior wall of urogenital sinus
- sinus separated by septum fuse → uterus and cervix

Question 27

Where does the myometrium arise from?

Answer 27

Surrounding mesenchyme of paramesonephric duct

Question 28

Where does the perimetrium arise from?

Answer 28

Peritoneal covering of paramesonephric duct

Question 29

What are the 2 origins of the vagina?

Answer 29

Upper: paramesonephric/mullerian ducts

Lower: Urogenital sinus

Question 30

How do the upper and lower parts of the vagina form 1 continuous lumen?

Answer 30

1) Sinovaginal bulbs from pelvic part of urogenital sinus proliferate to form solid vaginal plate

2) Completely canalise by 5th mth → lower part of vagina

3) Lumen separated from urogenital sinus by hymen

Question 31

What happens if the 2 paramesonephric ducts do not fuse?

Answer 31

Double uterus

Question 32

What causes a “rudimentary horn” in the uterus of a young px?

Answer 32

Underdevelopment of 1 of the paramesonephric ducts

Question 33

Describe the development of the female external genitalia.

Answer 33

1) Genital tubercle elongates slightly → Clitoris

2) Urethral folds → Labia minora

3) Genital swellings enlarge → Labia majora

4) Urogenital groove remains open → form vestibule

Question 34

What is a possible genital presentation of congenital adrenal hyperplasia in a female?

Answer 34

Development of male external genitalia
- elongation of penile tubercle
- formation of scrotum