Mesonephros

Mesonephros
Reconstruction of a human embryo of 17 mm. (Label for Mesonephros is at center right.)
Details
Carnegie stage	14
Days	22
Precursor	Intermediate mesoderm
Identifiers
Latin	Mesonephros
MeSH	A16.254.500
TE	E5.6.2.0.0.0.1
FMA	72171
Anatomical terminology []

The mesonephros (Greek: middle kidney) is one of three excretory organs that develop in vertebrates. It serves as the main excretory organ of aquatic vertebrates and as a temporary kidney in reptiles, birds, and mammals. The mesonephros is included in the Wolffian body after Caspar Friedrich Wolff who described it in 1759. (The Wolffian body is composed of : mesonephros + paramesonephrotic blastema)

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 humans, the mesonephros consists of units which are similar in structure and function to nephrons of the adult kidney. Each of these consists of a glomerulus, a tuft of capillaries which arises from lateral branches of dorsal aorta and drains into the inferior cardinal vein; a Bowman's capsule, a funnel like structure which surrounds the glomerulus; and a mesonephric tubule, a tube which connects the Bowman's capsule to the mesonephric duct. A unit consisting of a single glomerulus and the Bowman's capsule surrounding it is called renal corpuscle, and a unit consisting of single renal corpuscle with its associated mesonephric tubule is called a "nephron" or "excretory mesonephric unit".

Formation of each mesonephric nephron begins when a bit of the intermediate mesoderm adjacent to the mesonephric duct differentiates to form a mesonephric vesicle.

This vesicle then elongates to form the mesonephric tubule, attaching to the mesonephric duct on one side. Meanwhile, an artery from the dorsal aorta begins extending towards the mesonephric tubule. When these two structures contact each other, they form the glomerulus and the Bowman's capsule surrounding it. The mesonephric tubule is also known as the Wolffian tubules (or Kobelt's tubules).