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The mesonephros acts as a structure similar to the kidney that, in humans, functions between the sixth and tenth weeks of embryological life. Despite the similarity in structure, function, and terminology, however, the mesonephric nephrons do not form any part of the mature kidney or nephrons.
In the mature male, the function of this system is to store and mature sperm, and provide accessory semen fluid.The mesonephric duct (precursor of the male reproductive system) forms around the 3-4th week of pregnancy, present before the paramesonephric duct (precursor of the female reproductive system).
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.
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.
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 ...
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 mesonephros functions between the 6th and 10th weeks of embryological life of mammals as a temporary kidney, but serves as the permanent excretory organ of aquatic vertebrates. By 8 weeks post-conception, the human mesonephros reaches maximum size and begins to regress, with complete regression occurring by week 16. [6]
The urogenital ridge is made up of the gonadal anlage and the mesonephros. The mesonephros is involved in the development of the testis, but its role is in differentiation, and not determination. This is indicated by the absence of SRY expression in the mesonephros.