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1. either of two bean-shaped organs at the back of the abdominal cavity in man, one on each side of the spinal column. They maintain water and electrolyte balance and filter waste products from the blood, which are excreted as urine
2. the corresponding organ in other animals
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005


An organ involved with the elimination of water and waste products from the body. In vertebrates the kidneys are paired organs located close to the spine dorsally in the body cavity. They consist of a number of smaller functional units called urinary tubules or nephrons. The nephrons open to large ducts, the collecting ducts, which open into a ureter. The two ureters run backward to open into the cloaca or into a urinary bladder. In mammals, the kidneys are bean-shaped and found between the thorax and the pelvis. The number, structure, and function of the nephrons vary with evolution and, in certain significant ways, with the adaptation of the animals to their various habitats.

In its most primitive form, found only in invertebrates, the nephron has a funnel opening into the coelomic cavity followed by a urinary tubule leading to an excretory pore. In amphibians, some of the tubules have this funnel, but most of the tubules have a Bowman capsule (see illustration). In all higher vertebrates, the nephron has the Bowman capsule, which surrounds a tuft of capillary loops, called the glomerulus, constituting the closed end of the nephron. The inner epithelial wall of the Bowman capsule is in intimate contact with the endothelial wall of the capillaries. The wall of the capillaries, together with the inner wall of the Bowman capsule, forms a membrane ideally suited for filtration of the blood.

Nephron from frog kidney, dissected to show glomerulus within Bowman capsuleenlarge picture
Nephron from frog kidney, dissected to show glomerulus within Bowman capsule

The blood pressure in the capillaries of the glomerulus causes filtering of blood by forcing fluid, small molecules, and ions through the membrane into the lumen of Bowman's capsule. This filtrate contains some of the proteins and all of the smaller molecules in the blood. As the filtrate passes down through the tubule, the walls of the tubule extract those substances not destined for excretion and return them to the blood in adjacent capillaries. Many substances which are toxic to the organism are moved in the opposite direction from the blood into the tubules. The urine thus produced by each nephron is conveyed by the collecting duct and ureter to the cloaca or bladder from which it can be eliminated.

In all classes of vertebrates the renal arteries deliver blood to the glomeruli and through a second capillary net to the tubules. The major blood supply to the kidney tubules comes, however, from the renal portal vein, which is found in all vertebrates except mammals and cyclostomes. Waste products from the venous blood can thus be secreted directly into the urinary tubules. See Urinary system

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.


Either of a pair of organs involved with the elimination of water and waste products from the body of vertebrates; in humans they are bean-shaped, about 5 inches (12.7 centimeters) long, and are located in the posterior part of the abdomen behind the peritoneum.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Pfister, "The anatomic, radiologic and clinical characteristics of the pelvic kidney: an analysis of 86 cases," Journal of Urology, vol.
However, the presence of a pelvic kidney or previous pelvic surgery contraindicate this procedure.
The Wolffian ducts travel caudally, lateral to the pelvic kidney until they approach the caudal portion of the kidney where they migrate ventromedially and cross over the ventral surface of the pelvic kidney.
The normally positioned kidneys are outside the standard pelvic and para aortic fields, but the ectopic pelvic kidney is at risk of radiation nephritis.
The present case is unique, as cervical agenesis per se is an extremely rare anomaly, and, to the best of our knowledge, association with uterovesical fistula and a pelvic kidney has never been reported in the literature.
Femoral neuropathy following percutaneous nephrolithotomy of a pelvic kidney. Urology 1995;45:1059-61.
[8.] GULSUN M, BALKANCI F, CEKIRGE S, DEGER A, Pelvic kidney with an unusual blood supply: angiographic findings, Surg Radiol Anat, 2000, 22(1): 59-61.
Associated anomalies are Urological anomalies such as ureteropelvic junction obstruction, ectopic pelvic kidney, horseshoe kidney, renal hyo- or agenesis, megaureter, ureteral ectopy and ureterocele) are present in about one third of all EEC cases, predominantly in the EC population (1).
The umbilical arteries constitute the "arterial fork," which may hinder the ascent of the metanephros kidneys; as such, they remain in the vicinity of the iliac vessels, referred to as ectopic pelvic kidneys. When such kidneys cross to the contralateral side, opposite the ureteral insertion into the bladder, and then fuse/do not fuse with the other kidney, then they are referred to as crossed fused/unfused kidneys; for this, multiple postulates are proposed [3].
In addition other pelvic structures or pathologies may be mistaken for adnexal masses including duplicated uteri in mullerian anomalies pelvic kidneys or peritoneal inclusion cysts.
(9) reported their experience with 46 patients with anomalous kidneys (31 horseshoe, 4 crossed fused ectopic, 7 malrotated and 4 ectopic pelvic kidneys) and achieved complete clearance in all patients, similar to our results.
Critical analysis of outcome after open dismembered pyeloplasty in ectopic pelvic kidneys in a pediatric cohort.