Development of Urinary System

Question 1

State the 3 sets of excretory organs and from which germ layer it develops from

Answer 1

• Prenephros -> mesonephros -> metanephros

- Form from intermediate mesoderm

Question 2

Describe the prenephros

Answer 2

• Appears at start of week 4 and regressed at end of week 4
• Important as prenephric duct extends from the cervical region to the cloaca and drives the development of the next developmental stage

Question 3

What is the urogenital ridge

Answer 3

Urogenital ridge - region of intermediate mesoderm giving rise to both the embryonic kidney and gonad

Question 4

Describe the mesonephros

Answer 4

• Appears at end of week 4 and regressed end of week 8
• Mesonephric tubules develop caudal to the pronephric region
• Mesonephric tubules + mesonephric duct = embryonic kidney
• No water conserving function
• Mesonephric duct sprouts the ureteric bud which induces development of the definitive kidney

Question 5

Explain the metanephros

Answer 5

• Appears at week 5
• Ureteric bud is undifferentiated intermediate mesoderm, caudal to the mesonephros
  
  • Induces development of the true kidney
• Metanephros needs ureteric bud to function

Question 6

Explain the relationship between metanephros and ureteric bud

Answer 6

• Ureteric bud contacts metanephros
• Metanephros bud expands and branches which triggers mesoderm differentiation
• Forms the major and minor calyx

Question 7

Explain the positional change of the kidneys in embryology

Answer 7

• The ‘ascent’ of the kidney - more due to growth and descend of embryo trunk (light blue)
• Metanephric kidney first appears in the pelvic region and undergoes apparent caudal to cranial shift
• Crosses the arterial fork formed by vessels returning blood from the fetus to the placenta

Question 8

Explain the renal vessel origins

Answer 8

• Kidney gets new blood branches rather than carry original blood supply
  
  • Accessory renal arteries are old arteries
  • Act as end arteries - only supply to specific region of kidney
  • Risk of ischaemia to region of kidney if blocked

Question 9

Describe the urogenital sinus and how it develops

Answer 9

• Urogenital sinus - created from hindgut by urorectal septum
• Continuous with umbilicus
• Urachus closes to become the median umbilical ligament -
• Cloaca is divided into 2 - urorectal septum divides between urinary and GI system through rupturing of cloacal membrane

Question 10

Describe the locations of the male urethra segments

Answer 10

• Spongy - runs along shaft of penis
• Bulbous
• Membranous - passes through peritoneum
• Prostatic
• Pre-prostatic

Question 11

Describe congenital abnormalities involving movement of kidney

Answer 11

• Pelvic kidney - fails to migrate
  
  • Kidney can be trapped from umbilical artery
• Horseshoe kidney - as kidney moves up, they touch and fuse

Question 12

Describe congenital abnormalities involving ureteric bud

Answer 12

• Ureteric bud fails to interact with intermediate mesoderm
  
  • Renal agenesis - can survive with 1 kidney
• Duplication defects
  
  • Splitting of ureteric bud
  • Can result in 2 separate ureters
• Ectopic ureter
  
  • Splitting of ureteric bud
  • Can result in ectopic ureteral opening - present as incontinence (loss of urinary control)
  • Additional ureter can exit in other areas such as vagina and urethra
    
    • If it exits below the bladder sphincter, then incontinence occurs

Question 13

Explain hypospadias

Answer 13

• Defect in fusion of urethral folds

- Urethra opens onto the ventral surface rather than at the end of the glans