Development of the Urinary and Genital Systems

Question 1

What are the 3 different layers of the mesoderm?

Answer 1

para-axial, lateral plate, intermediate (where the urinary and genital structures come from)

Question 2

The intermediate mesoderm gives forms what ridge?

Answer 2

Mesonephric (Urogenital) Ridge

Question 3

The mesonephric ridge gives rise to what 3 things?

Answer 3

• 3 phases of kidney development
• the gonads
• most of the internal genital structures

Question 4

What are the primitive excretory systems in the embryo?

Answer 4

pronephros and mesonephros

Question 5

Describe the development of the pronephros

Answer 5

Around 24 days - starts in the cervical region and regress as soon as they develop (no function in humans)

Question 6

What does the mesonephric kidney consist of and it functions until what time?

Answer 6

Consists of a mesonephric duct and segmentally arranged mesonephric tubules
- functions through the 10th week of development

Question 7

How do the ureter and metenephric kidney form?

Answer 7

Through a reciprocal inductive process between the ureteric bud and metenephric blastema

Question 8

What is reciprocal induction?

how does the bud induce kidney development

Answer 8

If the bud doesn’t properly stimulate the mesoderm, then the kidney will never develop
- the ureteric bud grows outward and invades the mesochyme in the sacral region – and it induces the mesoderm to develop)

Question 9

Describe the formation of the renal pelvis and the renal calyces

Answer 9

• the first bifurcation of the ureteric bud forms the renal pelvis
• the collapse of the next 4 generations of bifurcations forms the major calyces and collapse of the following 4 forms of the minor calyces

Question 10

Describe the formation of the nephron

Answer 10

Metanephric tissue caps, induced by the tip of the collecting ducts, differentiate into a renal vesicle – which forms the Bowman’s capsule, proximal & distal convoluted tubules, and loops of Henle

Question 11

Consequence of early splitting of ureteric bud (what happens normally)

Answer 11

• normally, bud splits INSIDE mesoderm to give rise to the proper structures
• if it splits BEFORE mesoderm = duplicate or bifid ureter

Question 12

What is the ureteric bud attached to?

Answer 12

Mesonephric duct

Question 13

During what weeks do the kidneys ascend?

Answer 13

6th - 9th weeks

Question 14

What is a pelvic kidney?

Answer 14

One of the kidneys doesn’t ascend – remains in the false pelvis

Question 15

What is a horseshoe kidney (how is it formed)?

Answer 15

As the kidneys ascend, they tilt and turn inwards so that the hilum is medial – but sometimes, as they tilt, they touch - and the 2 inferior poles become fused to one another (they’re functionally separate but anatomically joined) – they get stuck under the IMA (don’t go all the way up)

Question 16

During what weeks does the partitioning of the cloaca happen?

Answer 16

4th - 6th weeks

Question 17

What is the partitioning of the cloaca?

Answer 17

The urorectal septum separates the cloaca into:

• anteriorly the primitive urogenital sinus
• posteriorly the rectum

Question 18

Primordial germ cells migrate from where to where? When does this happen?

Answer 18

From the lining of the yolk sac to the genital ridges

- in the 5th week

Question 19

How do the genital ridges arise?

Answer 19

Through a proliferation of coelomic epithelium cells which form primitive sex cords that surround the primordial sex cells

Question 20

By what week are the medullay and cortical regions discernible?

Answer 20

By the 6th week

Question 21

When and how do the paramesonephric ducts develop?

Answer 21

Develop in the 6th week as invaginations of the surface epithelium of the mesonephric ridge

Question 22

Cranial/caudal attachments of the paramesonephric ducts

Answer 22

Cranial: remain open to the coelomic cavity
Caudal: attach to the primitive urogenital sinus

Question 23

Gonads remain differentiated until what week?

Answer 23

7th week

Question 24

Gonad differentiation in males:

1. cortical cells?
2. medullary cords form?
3. leydig cells
4. what do the mesonephric ducts become?
5. what do the mesonephric tubules become?
6. what do the medullary cords become?

Answer 24

1. cortical cells degenerate
2. medullary cords form sertoli cells which produce AMH: cause paramesonephric ducts to degenerate
3. leydig cells of genital ridge produce testosterone
4. mesonephric ducts become ductus deferens
5. mesonephric tubules become rete testis
6. medullary cords become seminiferous tubules

Question 25

What is exstrophy of the bladder? When does it happen?

Answer 25

7th week

• mesonephric duct is drawn into the posterior wall of the bladder to form the trigone
• distal opening moves inferiorly to open into the primitive urethra

Question 26

What are the 3 accessory structures in the male?

Answer 26

Seminal glands
Prostate
Bulbourethral glands

Question 27

From what do the seminal glands arise?

Answer 27

From the ductus deferens (mesonephric duct) – mesodermal origin

Question 28

From what do the prostate and bulbourethral glands arise?

Answer 28

From the primitive urogenital sinus – endodermal origin

Question 29

Gonad differentiation in males:

1. cortical cells
2. medullary cords
3. mesonephric ducts

Answer 29

1. cortical cells remain and form secondary sex cords
2. medullary cords degenerate: no AMH produced = paramesonephric ducts remain to form the uterus and the uterine tubes
3. mesonephric ducts degenerate

Question 30

What are the remnants of the mesonephric ducts in the females?

Answer 30

epoophoron

paroophoron

Question 31

What happens to the paramesonephric ducts in the females?

Answer 31

Fuse in the midline and together attach to the posterior wall of the urogenital sinus

Question 32

What do the fused paramesonephric ductss form in the female?

Answer 32

Uterus and upper 1/3 of the vagina

Question 33

What does the cranial end of the paramesonephric ducts in the females form?

Answer 33

Remain unfused and develop into the uterine tubes

Question 34

What is the dual origin of the vagina?

Answer 34

• upper 1/3 paramesonephric ducts

- lower 2/3 urogenital sinus

Question 35

Where does the vaginal plate form? What does it develop into and when?

Answer 35

• Forms where the paramesonephric ducts fuse with the urogenital sinus
• Vaginal plate proliferates and canalizes by the 5th month to form the lower 2/3s of the vagina

Question 36

How is the broad ligament formed?

Answer 36

As the distal ends of the paramesonephric ducts fuse in the midline, the attached peritoneum is drawn medially – forms the broad ligament

Question 37

The gubernaculum in the female remains: what are its 2 derivatives?

Answer 37

round ligament of the uterus

ovarian ligament

Question 38

What does the urorectal septum do during the 7th week?

Answer 38

Fuses with the cloacal membrane to form the perineum – this divides the definitive urogenital sinus from the rectum and anus

Question 39

What forms the genital tubercle?

Answer 39

Cloacal folds on either side of the cloacal membrane merge anteriorly to form the genital tubercle

Question 40

What becomes the future urethra and what surrounds this structure?

Answer 40

Primitive urogenital sinus – urogenital folds flank the opening of the sinus

Question 41

Describe the differentiation of the female perineum:

• what happens to the genital tubercle?
• what forms the labia minora and majora?

Answer 41

• genital tubercle bends inferiorly to form the clitoris
• urogenital folds – labia minora
• labioscrotal folds – labia majora

Question 42

Describe the differentiation of the male perineum:

• what happens to the genital tubercle?
• what 2 things form the penile urethra?
• what do the labioscrotal folds form?

Answer 42

• genital tubercle elongates to form the shaft of the penis
• penile urethra is formed by:
  1. most distal part by evagination of ectoderm over glans
  2. urogenital folds fuse and enclose the definite urogenital sinus to form most of the urethra
• labioscrotal folds form the scrotum