Urogenital Development

Table of Contents:  

I. Primitive KidneyII. Internal GenitaliaIII. Definitive KidneyIV. External Genitalia

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Both the urinary and

genital components of the urogenital

system are derived, to a large extent,

from the intermediate mesoderm.

Species: Mouse Day Gestation: 8 Approx. Human Age: 22 days View: Transverse Cut

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The intermediate mesoderm becomes

segmented into units termed nephrotomes.

The lateral portions of the nephrotomes

unite, forming a longitudinal duct

on each side of the embryo

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The lumen of each nephrotome opens into the mesonephric duct as well as into the

body cavity. Glomeruli form as small vessels extend from the dorsal aortae.

Human Age: 27 days http://www.visembryo.com/baby/index.html

Removal of the lateral body wall

Species: Mouse Day Gestation: 9 Approx. Human Age: 28 days View: Lateral http://www.visembryo.com/baby/index.html

. . . illustrates the mesonephric duct

extending toward the cloacal region and the

openings of the nephric tubules into the body

cavity.

Species: Mouse Day Gestation: 9 Approx. Human Age: 28 days

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As development progresses, the nephrogenic tissues forms

urogenital ridges on the dorsal wall of the body cavity. The boxed area at higher magnification . . .

Species: Mouse Day Gestation: 10-11 Approx. Human Age: 5-6 weeks View: Transverse Cut

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. . . illustrates the mesonephric duct, the nephrotome, and the mesoderm

covering the urogenital ridge.

Species: Mouse Day Gestation: 10 Approx. Human Age: 5 weeks View: Transverse Cut

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The urogenital ridge consists of the mesonephros and the gonad.

The mesonephros consists of excretory tubules that contact a blood vessel medially and enter the

mesonephric (Wolffian) duct laterally. At higher magnification . . .

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. . . the relationships of the glomerular vessel, the duct and mesonephric tissue are seen.

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The gonads develop as primordial germ cells that form in the wall of the yolk sac close to the allantois migrate along the

dorsal mesentery of the hindgut to invade the genital ridges.

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The path of germ cell migration within the dorsal mesentery is shown on this micrograph.

Species: Mouse Day Gestation: 11 Approx. Human Age: 6 weeks View: Transverse Cut

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The primordial germ cells become surrounded by cells of the primitive sex cords. At this stage the gonad is "indifferent," as one cannot morphologically distinguish between the male and female.

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