ANHB2212 Study Guide - Final Guide: Gonad, Scrotum, Vas Deferens
3 Jun 2018
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The Kidneys
Development of the Kidneys:
• Develop from lateral plate mesoderm from intermediate mesoderm
• Becomes segmented starting at cranial end → nephrotome
• 3 different kidneys develop along this column → pronephros,
mesonephros, metanephros
• Pronephros
o Cavity develops inside intermediate mesoderm
o Ball of blood vessels from aorta bulge into this space →
glomerulus
o Allows excess water to leave blood without loss of salts and
macromolecules
o Seen in primitive freshwater fish
▪ Fresh water → more dilute than body fluids
▪ Water enters body → death by osmosis → rapid elimination
of water while retaining salts
o Initially water filters straight into coelom
o Later → cavity links up with other segments to form pronephric
duct
o In humans → segmental intermediate mesoderm in cervical region
▪ No function
▪ Degenerates by day 26
• Mesonephros
o Some primitive fish returned to the sea
▪ Reverse osmotic problem → dehydrate as salty medium
causes water to diffuse from blood
▪ Need to conserve water and eliminate salts
o Smaller glomerulus → less filtrate
o Larger system of tubules → reabsorption increased
o Important preadaptation to life on land
o Mesonephric kidney seen in bony fish and some amphibians
o Tubules connect to mesonephric duct and empty into cloaca
o In humans
▪ Appears early week 4
▪ Present in thoracic and lumbar regions
▪ Urine produced and drains through mesonephric ducts into
cloaca/bladder
▪ Week 5 → thoracic segments regress
▪ Mesonephric kidney functions until week 12
• Metanephros
o Kidney found in all higher vertebrates
o Week 5
▪ Ureteric buds sprout from mesonephric ducts
▪ Induce intermediate mesoderm in sacral region to form a
metanephros → contains capsules and tubules of nephrons
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