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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)

Structure

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.^[1]

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.^[1] 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"^[1] or "excretory mesonephric unit".^{[this quote needs a citation]}

Development

Mesonephric vesicle

Formation of each mesonephric nephron begins when a bit of the intermediate mesoderm adjacent to the mesonephric duct differentiates to form a mesonephric vesicle.^[1]

Mesonephric tubules

Enlarged view from the front of the left Wolffian body before the establishment of the distinction of sex.

a, b, c, d. Tubular structure of the Wolffian body.
e. mesonephric duct.
f. Its upper extremity.
g. Its termination in x, the urogenital sinus.
h. The duct of Müller.
i. Its upper, funnel-shaped extremity.
k. Its lower end, terminating in the urogenital sinus.

l. The genital gland.

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.^[1] The mesonephric tubule is also known as the Wolffian tubules (or Kobelt's tubules).

On the medial side of the mesonephric duct, from the sixth cervical to the third lumbar segments, a series of tubules, the Wolffian tubules, develops. They increase in number by outgrowths from the original tubules. The change from solid masses of cells to instead become hollowed in the center. One end grows toward and finally opens into the mesonephric duct, the other dilates and is invaginated by a tuft of capillary bloodvessels to form a glomerulus.^{[citation needed]}

Formation

The tubules collectively constitute the mesonephros.^{[citation needed]}

Function

The mesonephros as a whole produces urine from the 6th through the 10th week of development.^[1] Despite the similarity in structure, function, and terminology, however, the mesonephric nephrons do not form any part of the mature kidney or nephrons.^[1] As the more caudal nephrons form, the more cranial nephrons are already degenerating. In females the mesonephros degenerates entirely, though vestigial structures such as Gartner's ducts, the epoophoron, and paroophoron are common. In males, a few of the more caudal tubules will survive and give rise to the efferent ductules of the testis,^[1] the epididymis, vas deferens, seminal vesicle, as well as vestigial structures such as the appendix testis, appendix epididymis, and paradidymis.

Other animals

Section of the fold in the mesonephros of a chick embryo of the fourth day. Wolffian tubules are labeled to the right.

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, only the ducts and a few of the tubules of the mesonephros remain.

Additional images

Broad ligament of adult, showing epoöphoron.

References

^ ^a ^b ^c ^d ^e ^f ^g ^h "20.2 Development of the renal anlage". Human Embryology. Retrieved 21 May 2012.
^ Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 371–374. ISBN 0-03-910284-X.

UpToDate Contents

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1. 先天性腎尿路異常（CAKUT）の概要 overview of congenital anomalies of the kidney and urinary tract cakut
2. 腎無形成の出生前診断 prenatal diagnosis of renal agenesis
3. 異所性および癒合性異常腎 renal ectopic and fusion anomalies
4. 造血および幹細胞の機能の概要 overview of hematopoiesis and stem cell function
5. 先天性膣奇形の診断およびマネージメント diagnosis and management of congenital anomalies of the vagina

English Journal

CD45(low)c-Kit(high) cells have hematopoietic properties in the mouse aorta-gonad-mesonephros region.

Nobuhisa I, Yamasaki S, Ramadan A, Taga T.SourceDepartment of Stem Cell Regulation, Medical Research Institute, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8510, Japan; Department of Cell Fate Modulation, Institute of Molecular Embryology and Genetics/Graduate School of Pharmaceutical Sciences, Kumamoto University, Kumamoto, 860-0811, Japan.
Experimental cell research.Exp Cell Res.2012 Apr 1;318(6):705-15. Epub 2012 Jan 25.
Long-term reconstituting hematopoietic stem cells first arise from the aorta of the aorta-gonad-mesonephros (AGM) region in a mouse embryo. We have previously reported that in cultures of the dispersed AGM region, CD45(low)c-Kit(+) cells possess the ability to reconstitute multilineage hematopoietic
PMID 22289156

Astacin-like metallo-endopeptidase is dynamically expressed in embryonic stem cells and embryonic epithelium during morphogenesis.

Acloque H, Lavial F, Pain B.SourceLaboratoire de Génétique Cellulaire, INRA, ENVT, INRA UMR444, Castanet Tolosan, France. herve.acloque@toulouse.inra.fr
Developmental dynamics : an official publication of the American Association of Anatomists.Dev Dyn.2012 Mar;241(3):574-82. doi: 10.1002/dvdy.23737. Epub 2012 Jan 25.
BACKGROUND: Astacin-like metallo-proteases are zinc endopeptidases conserved among vertebrates and invertebrates. First described as hatching gland enzymes, many members of the family possess other functions during embryonic development. In the chick, however, functions of Astacin-like proteins rema
PMID 22275110

Japanese Journal

生殖腺に対するモノクローナル抗体の作製とその性状解析

横山智哉子
成蹊大学理工学研究報告 = The journal of the Faculty of Science and Technology, Seikei University 50(2), 57-62, 2013-12-01
… In a mouse, the genital ridge develops around embryonic day (E) 9.5 on the ventral surface of the mesonephros. …
NAID 120005426608

神経堤幹細胞の移動と多能性に関する解析

岡野栄之,名越慈人
自律神経 = The Autonomic nervous system 47(4), 304-307, 2010-08-15
NAID 10026905924

The origin of the first blood cell

YAMADA Yoshihiro
Aino journal 9, 27-29, 2010
… The pluripotent hematopoietic stem cells which are able to differentiate into all kinds of peripheral blood cell (including lymphocytes)are initially identified in the AGM (aorta-gonad -mesonephros)region at E10.5(definitive hematopoiesis).In vitro studies suggest the presence of hemangioblasts,which can differentiate into both blood and endothelial cells. …
NAID 110008731157

Related Pictures

★リンクテーブル★

リンク元	「後腎」「中腎」「mes」「mesonephric」

「後腎」

Mesonephros
	Reconstruction of a human embryo of 17 mm. (Label for Mesonephros is at center right.)
Details
Latin	Mesonephros
Carnegie stage	14
Days	22
Precursor	Intermediate mesoderm
Identifiers
Gray's	p.1205
MeSH	A16.254.500
TE	E5.6.2.0.0.0.1
FMA	72171
	Anatomical terminology