Development of the Kidney

Question 1

“3 sets of kidneys” + destiny

Answer 1

1. pronephros (3-4wks) ==> degenerate
2. mesonephros (4wks-2mos) ==> male reproductive ductwork
   
   1. First two stages help 3rd develop
3. metanephros (5wks-maturity) ==> definitive adult kidney

Question 2

Early development of “3 sets of kidneys”

Answer 2

• all structures develop from nephrogenic cord @ urogenital ridge
  
  • urogenital ridge = tissue runs lateral and ventral to dorsal aorta along coelom of embryo
• mesodermal cells @ nephrogenic cord ==> groups called nephrotomes
• nephrotomes vesiculate + join ==> eventually becomes mesonephric duct

Question 3

Characteristiscs of mesonephric duct/destiny of duct

Answer 3

• formed by fusion of nephrotomes w/in nephrogenic cord
• grows caudally to join developing cloaca
• remaining portion = “wolffian duct”
• males ==> epididymus and ductus deferens
• females ==> mostly degenerate

Question 4

Characteristics of urogenital ridge

Answer 4

• tissue that runs laterally and ventrally to the dorsal aorta lengthwise along the coelom of the embryo
• ==> wolffian body => protrudes further into coelom

Question 5

Characteristics of paramesonephric duct

Answer 5

• aka “Mullerian duct”
• develops along urogenital ridge
• runs along length of Wolffian body; joins w/cloaca
• males => degenerates
• females => forms oviduct and uterus

Question 6

Major aspects of development of metanephros

Answer 6

• ureteric bud
• collecting ducts and tubules
• glomeruli/nephron development

Question 7

Development of the ureteric bud

Answer 7

• =small bud of epithelial cells @ mesonephric duct
• eveloped by region of cells = metanephric blastema
• ureteric bud => lengthwise growth + branching => ureter + renal pelvis + major/minor calcyces

Question 8

Development of collecting ducts and tubules

Answer 8

• epithelia from ureteric bud ==> outgrowth tubules ==> parallel, aligned tubules = Malpighian pyramids
• these eventually become collecting ducts + collecting tubules

Question 9

Development of glomeruli/nephrons

Answer 9

• mesoderm @ metanephric blastema ==> metanephric spheroid @ tips of collecting tubules ==> metanephric vesicle
• vesicle elongates => tubule => S-floding => metanephric tubule ==> rest of nephron
  
  • fuses w/collecting tubules
  • forms envelop around glomerular capillaries = Bowman’s capsule
  • differetiates into different regions of nephron (PT, LOH, DCT)

Question 10

Development of the bladder/urethra

Answer 10

• urogenital sinus = originates as endoderm from cloaca
  
  • separates from hindgut @ 6-7wks
  • allantois degenerates => urachus (fibrous cord)
  • bladder and urethra form
• males
  
  • uteretic duct connects w/bladder
  • mesonephric duct separates and rejoins @ eventually connects w/urethra

Question 11

Kidney positioning during development

Answer 11

• as ureteric bud elongates => kidney ascends from sacral region => retroperitoneal location
• males: testes connected to wolffian duct descend