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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 ?
With one in ten Qatar residents believed to have some form of kidney disorder, an official from Hamad Medical Corporation's (HMC) Nephrology Division says recognizing World Kidney Day (WKD), observed annually on the second Thursday in March, is an important part of his team's efforts to raise awareness of the importance of good kidney health.
Even the officially approved medicines should be used very carefully particularly in patients already having kidney disorders. There are many medicines which have adverse effects on the kidneys.
The vaccination is available to people over 65, pregnant women, frontline healthcare workers and people with medical conditions such as heart, lung and kidney disorders.
It is available to people over 65, pregnant women, frontline healthcare workers and people with conditions such as heart, lung and kidney disorders.
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It is intended for physicians and other professionals involved in the care of patients with combined heart and kidney disorders, and can also be used as a reference textbook by medical students, residents, and fellows dealing with fluid overloaded and olilguric patients.
Proper nutrition is the first line of defense against common diseases and can also help people suffering from heart disease, kidney disorders and diabetes regain the strength their bodies need."- TradeArabia News Service
Interim Government Chair Roza Otunbaeva ordered to probe into procurement of hemodialysis machines, reported the press service of the Interim Government.After the leader of the provisional government visited the hemodialysis unit of the National Center of Cardiology and Therapy, the decision was made to allocate 85 million som for procurement of 25 hemodialysis machines and consumables for treatment of people with severe kidney disorders.However, some experts said later that this amount is unreasonably high for that amount of machines."Given that mass media are alternative source of information and taking int account media reports, Roza Otunbaeva made decision to carry out official investigation of that issue.
Birmingham Children's Hospital treats more than 1,500 youngsters with kidney disorders every year from as far afield as Coventry, Stoke, Northampton and mid-Wales.
SCIENTISTS have developed an artificial kidney which will help those suffering from kidney disorders to do away with the costly process of dialysis in future.
Kidney disorders can develop before a child is born.
No common medicine intake was found, although victims seem to typically be elderly men receiving treatment for high blood pressure, diabetes, and kidney disorders. A national epidemic alert was issued even though dengue fever, West Nile virus, and a number of other diseases have been ruled out.