The mesonephros is one of three excretory organs

Excretory system

The excretory system is a passive biological system that removes excess, unnecessary or dangerous materials from an organism, so as to help maintain homeostasis within the organism and prevent damage to the body. It is responsible for the elimination of the waste products of metabolism as well as...

 that develop in vertebrate

Vertebrate

Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

s. 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

Caspar Friedrich Wolff

Caspar Friedrich Wolff was a German physiologist and one of the founders of embryology.-Life:Wolff was born in Berlin, Brandenburg. In 1230 he graduated as an M.D...

 who described it in 1759. (The Wolffian body is composed of : mesonephros + paramesonephrotic blastema)

Structure

The mesonephros is composed of the mesonephric duct (also called the Wolffian duct), mesonephric tubules

Mesonephric tubules

Mesonephric tubules are genital ridges that are next to the mesonephros.In males, some of the mesonephric kidney tubules, instead of being used to filter blood like the rest, they "grow" over to the developing testes, penetrate it, and become connected to the seminiferous tubules of the testes.The...

, and associated capillary tufts. A single tubule and its associated capillary tuft is called a mesonephric excretory unit; these units are similar in structure and function to nephron

Nephron

The renal tubule is the portion of the nephron containing the tubular fluid filtered through the glomerulus. After passing through the renal tubule, the filtrate continues to the collecting duct system, which is not part of the nephron....

s of the adult kidney. The mesonephros is derived from intermediate mesoderm

Intermediate mesoderm

Intermediate mesenchyme or intermediate mesoderm is a type of mesoderm that is located between the paraxial mesoderm and the lateral plate.It develops into the part of the urogenital system * forms of urogenital system...

 in the vertebrate embryo.

Differences between males and females

In human males, the mesonephros gives rise to the efferent ductules of the testis, the epididymis

Epididymis

The epididymis is part of the male reproductive system and is present in all male amniotes. It is a narrow, tightly-coiled tube connecting the efferent ducts from the rear of each testicle to its vas deferens. A similar, but probably non-homologous, structure is found in cartilaginous...

, vas deferens

Vas deferens

The vas deferens , also called ductus deferens, , is part of the male anatomy of many vertebrates; they transport sperm from the epididymis in anticipation of ejaculation....

, seminal vesicle

Seminal vesicle

The seminal vesicles or vesicular glands are a pair of simple tubular glands posteroinferior to the urinary bladder of male mammals...

, and vestigial structures such as the appendix testis

Appendix testis

The appendix testis is a vestigial remnant of the Müllerian duct, present on the upper pole of the testis and attached to the tunica vaginalis. It is present about 90% of the time.-Clinical significance:...

, appendix epididymis, and paradidymis

Paradidymis

The term paradidymis is applied to a small collection of convoluted tubules, situated in front of the lower part of the spermatic cord, above the head of the epididymis....

.

The mesonephros largely regresses in human females, though vestigial structures such as Gartner's cysts, the epoophoron

Epoophoron

The epoophoron or epoöphoron is a remnant of the Mesonephric duct that can be found next to the ovary and fallopian tube.-Anatomy:...

, and paroophoron

Paroöphoron

The paroöphoron consists of a few scattered rudimentary tubules, best seen in the child, situated in the broad ligament between the epoöphoron and the uterus. Named for the Welsh anatomist David Johnson who originally described the structure at the University of Wales, Aberystwyth.It is a remnant...

 are common.

Differences among species

The mesonephros persists and forms the anterior portion of the permanent kidneys in fishes 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 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.

See also

• pronephros
  Pronephros
  Pronephros the most basic of the three excretory organs that develop in vertebrates, corresponding to the first stage of kidney development. 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...
  
  
• metanephros
• paramesonephric ducts, ducts beside (para-) the mesonephros