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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/09/20 11:23:12」(JST)

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Kidney development, or nephrogenesis, describes the embryologic origins of the kidney, a major organ in the urinary system. It is often considered in the broader context of the development of the urinary and reproductive organs.

Phases

The development of the kidney proceeds through a series of successive phases, each marked by the development of a more advanced kidney: the 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.

Pronephros

Main article: Pronephros

It develops in the cervical region of the embryo. During approximately day 22 of human gestation, the paired pronephroi appear towards the cranial end of the intermediate mesoderm. In this region, epithelial cells arrange themselves in a series of tubules called nephrotomes and join laterally with the pronephric duct. This duct is fully contained within the embryo and thus cannot excrete filtered material outside the embryo; therefore the pronephros is considered nonfunctional in mammals.

Mesonephros

Main article: Mesonephros

The development of the pronephric duct proceeds in a cranial-to-caudal direction. As it elongates caudally, the pronephric duct induces nearby intermediate mesoderm in the thoracolumbar area to become epithelial tubules called mesonephric tubules. Each mesonephric tubule receives a blood supply from a branch of the aorta, ending in a capillary tuft analogous to the glomerulus of the definitive nephron. The mesonephric tubule forms a capsule around the capillary tuft, allowing for filtration of blood. This filtrate flows through the mesonephric tubule and is drained into the continuation of the pronephric duct, now called the mesonephric duct or Wolffian duct. The nephrotomes of the pronephros degenerate while the mesonephric duct extends towards the most caudal end of the embryo, ultimately attaching to the cloaca. The mammalian mesonephros is similar to the kidneys of aquatic amphibians and fishes.

Metanephros

During the fifth week of gestation, the mesonephric duct develops an outpouching, the ureteric bud, near its attachment to the cloaca. This bud, also called the metanephrogenic diverticulum, grows posteriorly and towards the head of the embryo. The elongated stalk of the ureteric bud, called the metanephric duct, later forms the ureter. As the cranial end of the bud extends into the intermediate mesoderm, it undergoes a series of branchings to form the collecting duct system of the kidney. It also forms the major and minor calyces and the renal pelvis.

The portion of undifferentiated intermediate mesoderm in contact with the tips of the branching ureteric bud is known as the metanephrogenic blastema. Signals released from the ureteric bud induce the differentiation of the metanephrogenic blastema into the renal tubules. As the renal tubules grow, they come into contact and join with connecting tubules of the collecting duct system, forming a continuous passage for flow from the renal tubule to the collecting duct. Simultaneously, precursors of vascular endothelial cells begin to take their position at the tips of the renal tubules. These cells differentiate into the cells of the definitive glomerulus.

In humans, all of the branches of the ureteric bud and the nephronic units have been formed by 32 to 36 weeks of gestation. However, these structures are not yet mature, and will continue to mature after birth. Once matured, humans have an estimated one million nephrons (approximately 500,000 per kidney) or more.^{[citation needed]}

Migration

After inducing the metanephric mesenchyme the lower portions of the nephric duct will migrate caudally (downward) and connect with the bladder, thereby forming the ureters. The ureters will carry urine from the kidneys to the bladder for excretion from the fetus into the amniotic sac. As the fetus develops, the torso elongates and the kidneys rotate and migrate upwards within the abdomen which causes the length of the ureters to increase.

References

^ Bruce M. Carlson (2004). Human Embryology and Developmental Biology (3rd edition ed.). Saint Louis: Mosby. ISBN 0-323-03649-X.

External links

Gray's s252
University of Colorado
Overview - Edinburgh
University of Michigan
UNSW Embryology
University of Montreal: 3D animation male urogenital development
University of Montreal: 3D animation female urogenital development

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English Journal

ROBO2 restricts the nephrogenic field and regulates Wolffian duct-nephrogenic cord separation.

Wainwright EN1, Wilhelm D1, Combes AN1, Little MH1, Koopman P2.
Developmental biology.Dev Biol.2015 Aug 15;404(2):88-102. doi: 10.1016/j.ydbio.2015.05.023. Epub 2015 Jun 23.
ROBO2 plays a key role in regulating ureteric bud (UB) formation in the embryo, with mutations in humans and mice leading to supernumerary kidneys. Previous studies have established that the number and position of UB outgrowths is determined by the domain of metanephric mesenchymal Gdnf expression,
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Vitrification of kidney precursors as a new source for organ transplantation.

Marco-Jiménez F1, Garcia-Dominguez X2, Jimenez-Trigos E2, Vera-Donoso CD3, Vicente JS2.
Cryobiology.Cryobiology.2015 Jun;70(3):278-82. doi: 10.1016/j.cryobiol.2015.04.007. Epub 2015 Apr 24.
Kidney transplantation from deceased or living human donors has been limited by donor availability as opposed to the increasing demand, and by the risk of allograft loss rejection and immunosuppressive therapy toxicity. In recent years, xenotransplantation of developed kidney precursor cells has off
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The origin of the mammalian kidney: implications for recreating the kidney in vitro.

Takasato M1, Little MH2.
Development (Cambridge, England).Development.2015 Jun 1;142(11):1937-47. doi: 10.1242/dev.104802.
The mammalian kidney, the metanephros, is a mesodermal organ classically regarded as arising from the intermediate mesoderm (IM). Indeed, both the ureteric bud (UB), which gives rise to the ureter and the collecting ducts, and the metanephric mesenchyme (MM), which forms the rest of the kidney, deri
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Japanese Journal

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西川和範,西村耕太郎,王碧昭
日本生物工学会大会講演要旨集平成22年度, 174, 2010-09-25
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High Expression of Pitx-2 in the ICAT-deficient Metanephros Leads to Developmental Arrest

Hasegawa Yoshimi,Iizuka-Kogo Akiko,Akiyama Tetsu,Senda Takao
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ICAT (Inhibitor of β-catenin and T cell factor) inhibits the interaction between β-catenin and TCF/LEF transcription factor and serves as a negative regulator of Wnt signaling. In a subset of ICAT kno …
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