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Embryology of the Kidney

Embryology of the Kidney

Did you know that as humans we develop three kidneys? Well, you might be saying that cannot be for really because humans only have 2 kidneys. Well, don’t panic this article will take you through the development of the kidneys.

There are 3 stages in the development of the kidney:

  • Pronephros (A)
  • Mesonephros(B)
  • Metanephros(C)

Development of the Vertebrate Kidney. Source: Developmental Biology 8th edition, Fig.14.21(Part1)

1.  Pronephros

  • This is the first kidney
  • It develops during the 4th week of uterine life in the cervical region of the intermediate mesoderm.
  • The pronephros contains lots of segmental vesicles and has the pronephric duct that grows caudally toward the cloaca.
  • The pronephric duct is in the embryo and thus cannot filter materials outside the embryo. Therefore it is said that the pronephro kidney is nonfunctional in humans thus it degenerates.

2.  The Mesonephros (The 2nd Kidney)

  • The Mesonephros kidney follows the development pronephros in about the ending of 4th week of uterine life. It is also comes from intermediate mesoderm and is located in the throcolumbar area where the pronephric duct that was developed in the pronephos stage continue to elongated caudally and become the mesonephric tubules. Most of this tububles eventually degenerates but leave behind the Mesonephric duct or Wolffian duct which extends towards the cloaca
  • The  mesonephros is the functioning kidney during the 1st trimester and it produces urine during weeks 6-10.
  • It contributes to the:
    • Epipdymis
    • Vas deferens
    • Seminiferous tubules

3.  The Metanephros- The Permanent Kidney

A. Lateral view of a five-week embryo, showing the primordium of the metanephros or permanent kidney. B-E. Successive stages in the development of the metanephric diverticulum or ureteric bud (fifth to eight weeks). Observe the development of the ureter, renal pelvis, calices, and collecting tubules. The renal lobes, illustrated in E, are still visible in the kidneys of a 28-week fetus. (Modified from Moore KL, Persaud TVN. The Developing Human. Clinically Oriented Embryology (6th ed). Philadelphia: WB Saunders, 1998; with permission.)

Primoridium of the Metanephros of a Five-Week Embryo

  • This kidney begins to develop in the 5th week of the embryonic period.
  • It appears in the sacral region of the intermediate mesoderm
  • During the 5th week the Mesonephric duct fomr the mesonephros kidney develops an outgrowth called the ureteric duct. This duct is close to the attachment of the cloaca.
  • The ureteric duct eventually form the:

i.     ureter
ii.   renal pelvis
iii. major calyces
iv. minor calyces
v.   collecting tubules

The ureteric bud interacts with a portion of undifferentiated intermediate mesoderm called the metanephric mesenchyme. This interaction induces differentiation and thus the formation of the:

i.    renal tubles
ii.   glomerulus
iii. distal & proximal convoluted tubules
iv. Loops of Henle

If there is an abnormal interaction between the ureteric bud and the metanephric mesenchyme, several congenital malformation of the kidney may result.


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