F1 - The development of the apparatus urogenitalis

Question 1

What are the urinary- and reproductive organs developed from?

Answer 1

Intermediate mesoderm

Question 2

Which system of the urinary system and the genital system develops first?

Answer 2

Urinary system

Question 3

Development of the kidney

Answer 3

• Three sets of kidneys develop, which all derives from the urogenital ridge:
  
  1. Pronephros​ (first)
  2. Mesonephros (second)
  3. Metanephros (third)

Pronephros

• Appear early in the 4^th week
• A few cell clusters in the neck region
• Pronephric ducts runs caudally whcih extends from the cervical region → cloaca
• Rudimetary
• Ø function

Mesonephros

• Appear late in the 4^th week
• Function as interim kidneys until the permanent kidneys develop
• Consists of:
  
  • Glomeruli
  • Mesonephric tubules (opens into the mesonephric duct, receive capillaries from aorta, allowing filtration of blood)
  • Mesonephric ducts (opens into cloaca)
• Mesonephros degenerate the end of the 1^st trimester
• Mesonephric duct becom the efferent dutules of the testes
• The mesonephros develops caudally to the pronephros

Metanephros

• Forms the definitive kidney
• Develop in the 5^th week
• Starts function 4 week later
• Urine formation continues through fetal life
  
  • Urine is secreted into the amniotic cavity
• The permanent kidney develps from:
  
  • Uteric bud makes the collecting system
    
    • ​Primordium of:
      
      • Ureter (from stalk of the uteric bud)
      • Pelvis renalis
      • Calices
      • Collecting tubules (from cranial part of uteric bud)
    • An outgrowt from the mesonephric duct
    • Enter cloaca
    • The elongating bud penetrates the metanephrogenic blastema
  • Metanephric blastema makes the excretory system
    
    • ​Cellmass from nephrogenic cord
    • Forms the nephron​
    • Bowman’s capsule around glomerulus
      
      • ​Renal tubules: form small METANEPHRIC VESICLES
      • Metanephric vesicles → renal tubules
      • Glomeruli: proximal end of the renal tubules are invaginated to form the glomeruli
• The definitive kidney developes in the pelvic region, and then ascends to the abdomen
  
  • In the pelvis, the kidney receives its blood supply from a pelvic branch of the abdominal aorta and as it ascends, new arteries from the abdominal aorta supply the kidney
• The fetal kidney are subdivided into lobes
  
  • The lobulation disappears during infancy as the nephrons increase and grow

Question 4

Development of the kidney

Clinical relevance

Answer 4

• Horseshoe kidney:
  
  • A horseshoe kidney is where the two developing kidneys fuse into a single horseshoe-shaped structure.
  • This occurs if the kidneys become too close together during their ascent from the pelvis to the abdomen – they become fused and consequently ‘stuck’ underneath a. mesenterica caudalis
  • This type of kidney is still drained by two ureters
• Pelvic kidney:
  
  • ​Occurs when a kidney does not ascend from pelvis to abdomen
  • The kidney functions normally despite being in the wrong location

Question 5

Development of the bladder and urethra

Answer 5

• The bladder and urethra are derived from the cloaca
• The cloaca is divided into 2 parts by the uro-rectal septum:
  
  • ​Urogenital sinus
  • Canalis analis

Urogenital sinus:

• Divides into 3:
  
  • Upper urogenital sinus:
    
    • Bladder
  • Pelvic part:
    
    • Urethra (females)
    • Females: some of the female reproductive tract
    • Males: prostaticandmembranous urethra
  • Caudal part:
    
    • Urethra (males)
    • Females: reproductive tract
    • Males: spongy urethra

Canalis analis:

• Lig. umbilicale:
  
  • ​Remnant of the urachus
  • Connects the apex of the bladder to the umbilicus
• Trigonum vesicae:
  
  • ​As the bladder develops from the urogenital sinus, it absorbs the caudal parts of the mesonephric ducts, becoming trigonum vesicae
• Ureters:
  
  • ​Formed as outgrowths of the mesonephric ducts
  • Enter the bladder at the base of trigonum vesicae
• Bladder:
  
  • ​Mesonephric ducts:
    
    • ​Male: moves caudally, and becomes ductus ejaculatorius
    • Female: degenerate

Mesonephric ducts = Wolffian duct