Embryology Development of urogenital tract

Question 1

The urogenital system develops from?

Answer 1

Intermediate mesoderm

Question 2

What is the name of the longitudinal elevation that appears either side of the aorta?

Answer 2

Urogential ridge

Question 3

Of the urogenital ridge what is the name given to the part that develops into the urinary system/gential system?

Answer 3

Urinary system → Nephrogenic cord

Genital system → gonadal ridge

Question 4

The urinary system develops in 3 distinct regions.

What are theses regions? When do the develop & when are they functional?

Answer 4

Cranial → caudal
Pronephros, week 4, never functional
Mesonephros, week 4, function weeks 6-10
Metanephros, week 4, functions from week 12

Question 5

What is the origin of

1) excretory units
2) collection ducts

Answer 5

1) Metanephric mesoderm (matenephric blastema)

2) Ureteric bud (outpouch of mesonephric duct)

Question 6

How does the position of the kidney change during development?

Answer 6

Develops in pelvis region, ascends to more cranial position and rotates by 90 degrees.

Question 7

Renal agenesis can occur if…

How common is unilateral agenesis?

Answer 7

the ureteric bud fails to contact and/or induce the metanephric mesoderm
1/1000 more common on the L and in males. Associated with single umbilical artery

Question 8

Bilateral renal genesis

Answer 8

Oligohydraminos
1/3000
Characteristic facial appearance → potters sequence

Question 9

How does a duplication of the kidney occur?

Answer 9

Early splitting of ureteric bud, may be partial or complete

Question 10

Why do accessory renal arteries form? How common is this?

Answer 10

Persistence of embryonic vessels formed during the ascent of the kidney.
25% of adult kidney have 2-4 renal arteries.

Question 11

What structure is the forming bladder continuous with?

When it obliterates what is it remnant called?

Answer 11

The bladder is continuous with the allantois. Becomes obliterated to form the urachus (median umbilical ligament)

Question 12

What are the organs of the epithelium of the urethra and the surrounding connective tissue/smooth muscle?

Answer 12

Inner epithelium: Endoderm

Outer smooth: Mesoderm

Question 13

Why does a urachal fistula or urachal cyst form?

Answer 13

Urachal fistula: entire urachus remains open

Urachal cyst: small area persists

Question 14

What is bladder exstrophy?

Answer 14

At birth, posterior wall of bladder protrudes through the abdominal wall, associated epispadias and wide separation of pubic bones.

Cause by lack of migration and incomplete closure of the inferior abdominal wall.

Question 15

What is potters sequence, what is the cause?

Answer 15

Severe Oligohydramnios →
Pulmonary hypoplasia (no space/minmal amino acids)
Developemental abnormality: Limb deformity, epicanthic folds, flattened face, low set ears  

20 weeks >20weeks - fetal urine produces amniotic fluid.

• Bilateral renal agenesis or
• atresia of urether or uretha
• PPROM
• Ueteroplacental insufficiency

Question 16

Potters sequence diagnosis:

Prognosis

Answer 16

• USS during 2nd trimester

Often stillbirth or dies in first days of life

Question 17

When are where do the genital/gonadal ridges form?

Answer 17

Week 4, thickened area of mesothelium on medial side of mesonephros - remains indifferent until week 7

Question 18

How and when to the primordial germ cells enter the genital ridge?

Answer 18

From yolk sac migrate along the dorsal mesentery invading the ridge at week 6

Question 19

What gene on the short arm of the Y chromosome determines the differentiation of the gonads?

Answer 19

SRY gene sex determining region

Question 20

At how many weeks is testosterone produced & where from?

Answer 20

Leydig cells

From week 7

Question 21

How does the oogine become surround in epithelial cells that become the follicular cells?

Answer 21

At 4 months surface epithelium form cords that surround the germ cells and separate.

Question 22

What does the mesonephric duct (wolffian) form in the male?

Answer 22

Duct of epididymis
Ductus deferens
Ejaculatory duct and seminal visible
Ureter/renal pelvis/calyces and collecting tubes

Question 23

What does the paramesonephric duct from in females?

Answer 23

Uterine tube, uterus, hydatid

Question 24

What is a gartners cyst?

Answer 24

Persisting mesonephric duct- develops as cyst in uterus or vagina

Question 25

Explain the indifferent stage of the external genitalia

Answer 25

At week 3, cloacal membrane fold & unit in midline forming the genital tubercle divided into anterior urethral folds and posterior anal fold.

Either side of urethral folds a swelling becomes apparent - genital swelling (form scrotal swelling in men or labia majora in females)

Question 26

What happens to the external genitalia in the presence of androgens?

Answer 26

The genital tubercle elongates (forming the phallus) and the urethral grove closes forming the penile urethra.
The labioscrotal swelling fuse to form the scrotum

Question 27

What is androgen insensitivity hormone?

Answer 27

XY chromosome but due to sensitivity to testosterone, external gentialia develop as female, testes do not descend (cyptochordism) but tests still produce anti-mullairan hormone so the uterus/uterine tubes do not develo, vagina ends in blind pouch. No mesus.

X linked recessive

Question 28

What is hypospadias?

Answer 28

Failure of fusion of urethral folds

1/300 males

Question 29

What is epispadias

What other condition is it associated with?

Answer 29

Genital tubercule developers in region of urorectal septum.
Urethra on the dorsal of penis
1/30000
Associated with exstrophy of the bladder

Question 30

Describe the descent of the testes

Answer 30

Testes descend with the degeneration of the mesonephros, the follow the gebernaculum to the anterior abdominal wall, by week 12 reaches the inguinal canal and by week 28 passes through & reaches the scrotum by week 33.

As the the testes descend from the abdominal cavity into the testes it forms an extension called the processes vaginalis which is obliterated at birth.

Question 31

What is the origin of the vagina?

Answer 31

Urogenital sinus - sinovaginal bulbs → failure to form causes absence of vagina/uterus

Question 32

What is cryptochidism?
Incidence
Managemnt

Answer 32

undescended testes
30% premature infants, 3-4% term
Most cases they descend by the end of the 1st year. If stay in the abdomen at end of 1st year - likely sterility
Often caused by deficient testosterone