Embryology - Legends

Question 1

When do the genitals first start developing?

Answer 1

Week 5-6

Question 2

How do the genitals first appear?

Answer 2

As the genital or gonadal ridge. A thickening of the medial part of the mesonephros

Question 3

What are the primitive sex cord?

Answer 3

Structures fromed from mesenchyme of Genital ridges.
They receive Germ cells from the yolk sac

Question 4

How do germ cells reach the primitive sex cords?

Answer 4

In wk 6 germ cells migrate from the yolk sac –> Dorsal mesentery –> Primitive sex cords

Question 5

What happens when germ cells migrate to the primitive sex chords?

Answer 5

They form a structure called the Indifferent Gonad

Question 6

What happends after formation of the indifferent gonad?

Answer 6

Mesonephric epithelium invaginates to form the paramesonephric duct

Question 7

Where is the paramesonephric duct found and where does it go?

Answer 7

Its lateral to the mesonephros and developing gonads.

The cranial end enters peritoneal cavity –> passes ventrally over mesonephric ducts –> enters dorsal wall of urogenital sinus

Question 8

What happens to the indifferent Gonad?

Answer 8

Forms the testis

Question 9

What happens to the mesonephric duct?

Answer 9

Forms:
- Epidydimis
- Vas Deferens
- Seminal Vescle

Question 10

What happens to the paramesonephric duct?

Answer 10

Degenerates

Question 11

What happens to the urogenital sinus?

Answer 11

Forms
Bladder
Urethra
Prostate

Question 12

What gene is responsible for determining testes vs ovaries?

Answer 12

SRY (sex determing region Y) on the Y chromosome encodes for a protein called TDF (Testis determining factor) that triggers testes development

Question 13

Describe the actions of SRY

Answer 13

Makes TDF –> Indifferent Gonad –> Testis

Found in Primordial Supporting Cells within the sex chords –> Sertoli cells

Question 14

How are sertoli cells involved in development of the testes?

Answer 14

They’re created from Primordial Supporting Cells that express SRY

They secrete MIS (Mullerian Inhibiting Substance):
1) Paramesonephric duct degenerates
2) Mesenchymal cells between sex cords –> Leydig Cells

Question 15

What do Leydig cells do to develop the individuals sex?

Answer 15

They produce testosterone –> masculine differentiation of mesonephric ducts and male external genitalia

Question 16

So in wk 5 Primary sex cords, medulla and cortex of testes develop. Wk 6 germ cells are incorporated. Wk 7 TDF stimulates formation of seminiferous tubules.
What happens next?

Answer 16

Seminiferous tubules branch and the ends anastomose to form the rete testis

Tunica Albuginea replaces surface mesothelium

Question 17

What do the seminal vesicles develop from?

Answer 17

Caudal end of the mesonephric duct

Question 18

What does the prostate develop from?

Answer 18

The urethra, before that the urogenital sinus

Question 19

The gonads are required to descend, where do they originally form?

Answer 19

In the lumbar region

Question 20

Describe the descent of the testes?

Answer 20

Week 7 - T10

Week 12 - Deep inguinal ring

Week 39 (just before birth) - Enters scrotum

Testes are aided in their descent by the larger inguinal canal of males

Question 21

Whats the main developmental abnormality of the male genitalia?

Answer 21

Cryptorchidism aka testes absent from scrotum

Question 22

What are the possible reasons for cryptorchidism?

Answer 22

1) Undescended
2) Ectopic
3) Retractile testes
4) Absent testes

Question 23

What are the complications of cryptorchidism?

Answer 23

Infertility
Germ cell Tumours
Testicular Torsion

Question 24

How do we manage cryptorchidism?

Answer 24

Orchiopexy (surgically move the testes into the scrotum)