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The development of the kidney proceeds through a series of successive phases, each marked by the development of a more advanced kidney: the archinephros, pronephros, mesonephros, and metanephros. [1] The pronephros is the most immature form of kidney, while the metanephros is most developed. The metanephros persists as the definitive adult kidney.
The mesonephros persists and forms the anterior portion of the permanent kidneys in fish and amphibians, but in reptiles, birds, and mammals, it atrophies and for the most part disappears rapidly as the permanent kidney (metanephros) begins to develop [2] during the sixth or seventh week. By the beginning of the fifth month of human development ...
The mesonephros persists and form the permanent kidneys in fish and amphibians, but in reptiles, birds, and mammals, it atrophies and for the most part disappears rapidly as the permanent kidney (metanephros) develops beginning during the sixth or seventh week, so that by the beginning of the fifth month only the ducts and a few of the tubules ...
Mesonephros develops after the pronephros, replacing it. The mesonephros is the final kidney in amphibians and most fish. In more advanced vertebrates , mesonephros develops during embryogenesis and is then replaced by the metanephros. [36] In reptiles and marsupials, it remains functional for some time after birth along with the metanephros.
Then, caudal to the pronephros, the mesonephros develops, which is the functioning kidney of the embryo. [166] [167] Subsequently, the mesonephros degrades in females, and in males it participates in the development of the reproductive system. The third stage is the formation of the metanephros in the caudal part of the embryo.
It is succeeded by the mesonephros, which in fish and amphibians remains as the adult kidney. In amniotes, the mesonephros is the embryonic kidney and a more complex metanephros acts as the adult kidney. [1] Once a more advanced kidney forms, the previous version typically degenerates by apoptosis or becomes part of the male reproductive system.
The nephrogenic cords are located on the posterior wall of the embryo, which is where the kidneys are located. The nephrogenic cords go through three phases of development which overlap to some extent, both in space and in time. The 1st phase is the pronephros, the 2nd phase is the mesonephros and the 3rd and final stage is the metanephros.
As development proceeds, the intermediate mesoderm differentiates sequentially along the anterior-posterior axis into three successive stages of the early mammalian and avian urogenital system, named pronephros, mesonephros and metanephros respectively (anamniote embryos form only a pronephros and mesonephros). [2]