Kidney development

Kidney development

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.

Contents

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

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

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

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

External links


Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать реферат

Look at other dictionaries:

  • Kidney — For other uses, see Kidney (disambiguation). Kidney Human kidneys viewed from behind with spine removed Latin ren Artery …   Wikipedia

  • Kidney transplantation — or renal transplantation is the organ transplant of a kidney in a patient with end stage renal disease. Kidney transplantation is typically classified as deceased donor (formerly known as cadaveric) or living donor transplantation depending on… …   Wikipedia

  • Kidney (TCM) — As distinct from the Western medical concept of Kidneys, this concept from Traditional Chinese Medicine is more a way of describing a set of interrelated parts than an anatomical organ. (See Zang Fu theory)To differentiate between western or… …   Wikipedia

  • Development of the urinary and reproductive organs — The development of the urinary and reproductive organs as a part of the prenatal development, concerns the urinary system and sex organs. The latter is a part of the stages of sexual differentiation. The urinary and reproductive organs are… …   Wikipedia

  • Kidney stone — Classification and external resources …   Wikipedia

  • Kidney stone — 1. A stone in the kidney (or lower down in the urinary tract). Kidney stones are a common cause of blood in the urine and pain in the abdomen, flank, or groin. Kidney stones occur in 1 in 20 people at some time in their life. The development of… …   Medical dictionary

  • Kidney Foundation of Canada — The Kidney Foundation of Canada is people working together for a common cause. We are volunteers, individuals living with kidney disease, donors, and staff members from all walks of life, all across Canada. Since its creation in 1964, The Kidney… …   Wikipedia

  • kidney transplant — or renal transplant Replacement of a diseased or damaged kidney with one from a living relative or a legally dead donor. The former s tissue type is more likely to match, reducing the chance of rejection; but removal puts the donor at risk, and a …   Universalium

  • Kidney — One of a pair of organs located in the right and left side of the abdomen which clear "poisons" from the blood, regulate acid concentration and maintain water balance in the body by excreting urine. The kidneys are part of the urinary… …   Medical dictionary

  • Kidney — Recorded as Kidney, Kydney, Kidder, and Kidner, this most interesting surname is Anglo Irish. If Irish it is now chiefly to be found in County Cork, as an anglicized form by pseudo translation of the Old Gaelic name O Dubhain. It would seem that… …   Surnames reference

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”