197. UG Development

Question 1

When do males and females differentiate in utero? What structures are male and what are female?

What become of the following UG primordia?

• Intermediate Mesoderm
• Splanchnopleure of Hindgut
• Somatopleure

Answer 1

W8
Mesonephric duct = males
Paramesonephric duct = females

IM - Kidney/Gonads
Hindgut - bladder/urethra
Somatopleure - genitals (Genital tubercle = swelling of somatopleure in perineum)

Question 2

UG Ridge

• what is it
• what does it contain (2)
• how do primordial germ cells develop?
• how do the ducts develop?

Answer 2

Intermediate mesoderm that bulges into peritoneal cavity
1. Nephrogenic cord (kidney)
2. Gonadal Ridge (gonads) - thickening epithelium
Germ cells migrate from hindgut into gonadal ridges (surrounded by epithelial sex cords that project into primitive gonad)

Paramesonephric duct: invagination of surface that persists as opening of uterine tubes, both sides join to form uterus/vagina

Mesonephric duct: condensations of intermediate mesoderm (nephrogenic cord) = becomes female ureter, or male ductus deferens (changes fx from urine to genital)

Question 3

What are the 3 sequential kidneys during development?

How does the mesonephric duct form? drain? what originates from it?

What does the metanephros include (2) - what do they give rise to?

How does the kidney get to it’s place in the neonate?

What is horseshoe kidney?

Answer 3

1. Pronephros (Cranial, vestigial)
2. Mesonephros (Huge, first fx-ing)
3. Metanephros (Caudal, kept as adult)

Mesonephric duct: joins mesonephric tubues of first functioning kidney, drains into cloaca (hindgut dilation), becomes first (temporary) ureter, AKA wolffian duct; Metanephric diverticulum (ureteric bud) originates from mesonephric duct (mesodermal origin)

Metanephros: 1. Ureteric bud (from mesonephric duct, gives rise to ureters, renal pelvis, calyces, collecting tubules in pyramids), 2. metanephric mass of intermediate mesoderm - gives rise to kidney nephrons

Kidneys ascend as mesonephros degenerates downwards; as kidney ascends, sequential arteries hook up to it; ureters and blood vessels are anterior to developing kidney

Horseshoe Kidney: fusion of ureteric buds around IMA as they ascend

Question 4

UG Sinus (Cloacal Separation)

• what divides cloaca?
• three parts of UG sinus
• what occurs due to improper cloacal division?
• what happens to allantois?
• what is exstrophy of bladder/cloaca?

Answer 4

Urorectal Septum divides cloaca into rectum and UG Sinus (Mesodermal)
1. Bladder, 2. Pelvic, 3. Phallic = all continuous with allantois (vestigial)
Improper division: Fistula & imperforate anus (rectum + perineum/urethra/bladder/vagina)

Allantois: becomes fibrous cord (Urachus) from naval to top of bladder, may persist as cyst, sinus, fistula

Exstrophy of bladder/cloaca: failure of mesoderm migration into cloacal membrane/ventral abd wall = breakdown of ant bladder wall exposing mucosa

• bladder breaks thru abd wall
• cloaca breaks down and hindgut breaths thru body wall

Question 5

Sexual Differentiation

• how do testes develop?
• how do ovaries develop?
• how do external genitals develop (derivatives)?
• what is hypospadius?

Answer 5

Testes: Primary sex cords = seminiferous tubules = sertoli cells (through whole thickness of testes), no secondary sex cords

Ovaries: Primary sex cords: vestigial rete ovarii
Secondary sex cords = ovarian follicles (near cortex) = Granulosa cells

Genitalia

• Labioscrotal folds: flank UG folds + genital tubercle = Labia majora or scrotum
• Lower UG Sinus: female vestibule; male penile urethra
• UG Folds: female labia minora
• Clitoris = Penis
• Penile Urethra: most from ventral fusion of UG sinus, navicular fossa = ectodermal invagination

Hypospadius: failure of UG folds to fuse
- urethral opening on ventral surface of penis

Question 6

What are the adult derivatives of the UG sinus? Mesonephric Duct? Paramesonephric duct?

Answer 6

UG Sinus: Bladder, Urethra, Paraurethral Glands, Uterus, Upper vagina, vaginal plate, greater vestibular gland

Mesonephric Duct: Ureter (Male: Epididymus, Efferent Ductules, Ductus Deferens, Seminal Vesicles, Ureters)

Paramesonephric Duct: Uterus, Uterine Tube

Ovary: intermediate mesoderm