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 tract. The urine then passes through connecting tubes called "ureters" into the bladder. The bladder stores the urine until it is released during urination. The kidneys remove waste products from the blood and produce urine. As blood flows through the kidneys, they filter waste products, chemicals, and unneeded water from the blood. Urine collects in the middle of each kidney, an area called the renal pelvis. Urine then drains from the kidney through a long tube, the ureter, to the bladder, where it is stored. The kidneys also make substances that help control blood pressure and regulate the formation of red blood cells.
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One of the paired organs that excrete urine. The kidneys are bean-shaped organs (about 11 cm long, 5 cm wide, and 3 cm thick) lying on either side of the vertebral column, posterior to the peritoneum, about opposite the twelfth thoracic and first three lumbar vertebrae. SYN: nephros, ren. [A.S. cwith, womb, belly, + neere, k. (L. ren, G. nephros)]
- amyloid k. a k. in which amyloidosis has occurred, usually in association with some chronic illness such as multiple myeloma, tuberculosis, osteomyelitis, or other chronic suppurative inflammation; such kidneys are moderately enlarged and grossly manifest a waxy appearance, with amyloid deposited beneath the endothelium in the glomerular loops and in the arterioles, apparently beginning as foci of thickening of the basement membranes. SYN: waxy k..
- Armanni-Ebstein k. glycogen vacuolization of the loops of Henle, seen in diabetics before the introduction of insulin. SYN: Armanni-Ebstein change.
- arteriolosclerotic k. a k. in which there is sclerosis of the arterioles, i.e., arteriolar nephrosclerosis resulting from long-standing benign hypertension. Such kidneys tend to be pale red-brown or relatively gray, moderately reduced in size, and firmer than normal organs; the capsular surfaces are uniformly finely granular. Most of the arterioles are thickened and hyalinized, thereby resulting in varying degrees of narrowing of the lumens, ischemia, and fibrosis in the interstitial tissue, leading to uniform contraction of the cortex.
- arteriosclerotic k. a k. in which there is sclerosis of arterial vessels larger than arterioles. Such kidneys are usually not significantly reduced in size, but are likely to be paler than usual; the capsular surface may be marked by a few, possibly several, conical, relatively deep V-shaped scars that result from fibrosis and ischemic atrophy of the region supplied by the affected vessel.
- artificial k. SYN: hemodialyzer.
- Ask-Upmark k. true renal hypoplasia with decreased lobules and deep transverse grooving of the cortical surfaces of the k..
- atrophic k. a k. that is diminished in size because of inadequate circulation and/or loss of nephrons.
- cake k. a solid, irregularly lobed organ of bizarre shape, usually situated in the pelvis toward the midline, produced by fusion of the renal anlagen.
- contracted k. a diffusely scarred k. in which the relatively large amount of abnormal fibrous tissue and ischemic atrophy leads to a moderate or great reduction in the size of the organ, as in arteriolar nephrosclerosis and chronic glomerulonephritis.
- cow k. a k. containing an abnormally large number of minor calices, resembling normal bovine renal anatomy.
- crush k. acute oliguric renal failure following crushing injuries of muscle; kidneys show the changes of hypoxic tubular damage, plus pigment casts in renal tubules that contain myoglobin.
- cystic k. a general term used to indicate a k. that contains one or more cysts, including polycystic disease, solitary cyst, multiple simple cysts, and retention cysts (associated with parenchymal scarring).
- disk k. SYN: pancake k..
- duplex k. a k. in which two pelviocaliceal systems are present.
- fatty k. a k. in which there is fatty metamorphosis of the parenchymal cells, especially fatty degeneration.
- flea-bitten k. the k. seen at autopsy in some cases of bacterial endocarditis, the appearance being caused by diffuse petechial hemorrhages resulting from focal glomerulonephritis.
- floating k. the abnormally mobile k. that frequently descends to the brim of the pelvis when the patient assumes the erect position; nephroptosis. SYN: movable k., wandering k..
- Formad k. an enlarged and deformed k. sometimes seen in chronic alcoholism.
- fused k. a single, anomalous organ produced by fusion of the renal anlagen.
- Goldblatt k. a k. whose arterial blood supply has been compromised, as a consequence of which arterial (renovascular) hypertension develops.
- granular k. a k. in which fairly uniform, diffusely and evenly situated foci of scarring of the interstitial tissue of the cortex (and sometimes scarring of glomeruli), and the associated slight degree of bulging of groups of dilated tubules, leads to the development of a minutely bosselated surface; such kidneys are seen in arteriolar nephrosclerosis or chronic glomerulonephritis. SYN: sclerotic k..
- head k. SYN: pronephros (1).
- hind k. SYN: metanephros.
- horseshoe k. union of the lower or occasionally the upper extremities of the two kidneys by a band of tissue extending across the vertebral column.
- medullary sponge k. cystic disease of the renal pyramids associated with calculus formation and hematuria; differs from cystic disease of the renal medulla in that renal failure does not usually develop.
- middle k. SYN: mesonephros.
- mortar k. SYN: putty k..
- movable k. SYN: floating k..
- pancake k. a disk-shaped organ produced by fusion of both poles of the contralateral k. anlagen. SYN: disk k..
- pelvic k. a congenital abnormality in which the k. is in the pelvis; usually the arterial blood supply comes off the bifurcation of the aorta or the iliac artery.
- polycystic k. a progressive disease characterized by formation of multiple cysts of varying size scattered diffusely throughout both kidneys, resulting in compression and destruction of renal parenchyma, usually with hypertension, gross hematuria, and uremia leading to progressive renal failure. There are two major types: 1) with onset in infancy or early childhood, usually of autosomal recessive inheritance [MIM*263200]; 2) with onset in adulthood, of autosomal dominant inheritance with genetic heterogeneity [MIM*173900, 173910, and 600666]; may be caused by mutation in either polycystin-1 gene on chromosome 16p, polycystin-2 gene on 4q, or gene(s) not identified yet. SYN: polycystic disease of kidneys.
- putty k. a k. containing caseous material trapped by stricture of the ureter due to tuberculous granulations in renal tuberculosis. SYN: mortar k..
- pyelonephritic k. a k. deformed by multiple scars as a result of chronic or recurrent renal infection.
- Rose-Bradford k. a form of fibrotic k. of inflammatory origin found in young persons.
- sclerotic k. SYN: granular k..
- sigmoid k. upper pole of one k. fused with the lower pole of the other.
- supernumerary k. a k., in addition to the two usually present, developed from the splitting of the nephrogenic blastema or from a separate metanephric blastema, into which a partial or complete duplication of the ureteral stalk enters to form a separate, capsulated k.; in some cases, the separation of the duplicated organ is incomplete.
- thoracic k. ectopic k. that partially lies above the diaphragm in the posterior mediastinum.
- wandering k. SYN: floating k..
- waxy k. SYN: amyloid k..

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kid·ney 'kid-nē n, pl kidneys
1) one of a pair of vertebrate organs situated in the body cavity near the spinal column that excrete waste products of metabolism, in humans are bean-shaped organs about 41/2 inches (111/2 centimeters) long lying behind the peritoneum in a mass of fatty tissue, and consist chiefly of nephrons by which urine is secreted, collected, and discharged into the pelvis of the kidney whence it is conveyed by the ureter to the bladder compare MESONEPHROS, METANEPHROS, PRONEPHROS
2) any of various excretory organs of invertebrate animals

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either of the pair of organs responsible for the excretion of nitrogenous wastes, principally urea, from the blood. The kidneys are situated at the back of the abdomen, below the diaphragm, one on each side of the spine; they are supplied with blood by the renal arteries. Each kidney is enclosed in a fibrous capsule and is composed of an outer cortex and an inner medulla. The active units of the kidney are the nephron, within the cortex and medulla, which filter the blood under pressure and then reabsorb water and selected substances back into the blood. The urine thus formed is conducted from the nephrons via the renal tubules into the renal pelvis and from here to the ureter, which leads to the bladder. See also haemodialysis, horseshoe kidney, renal function tests.

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kid·ney (kidґne) [Middle English kidenei] either of the two organs in the lumbar region that filter the blood, excreting the end-products of body metabolism in the form of urine, and regulating the concentrations of hydrogen, sodium, potassium, phosphate, and other ions in the extracellular fluid. Called also ren [TA]. Each human kidney is about 11 cm long, 5–7.5 cm wide, and 2.5 cm thick, and weighs from 120 to 160 g. The kidney is of characteristic shape, with a notch known as the hilum on its inner, concave border; renal vessels and nerves and the ureter pass through it, and it communicates with the cavity or sinus of the kidney. The kidney consists of a cortex (see renal cortex, under cortex) and a medulla (see renal medulla, under medulla). The medullary substance forms pyramids, whose bases are in the cortex and whose apices, the renal papillae, project into the calices of the kidney. The renal pyramids number from 10 to 15. The parenchyma of each kidney is composed of about one million renal tubules (nephrons, the functional unit of the kidney), held together by a little connective tissue. Each tubule begins blindly in a renal corpuscle, consisting of a glomerulus and the surrounding glomerular capsule, situated within the cortex. After a neck or constriction below the capsule, it becomes the proximal convoluted tubule, then Henle loop, then the distal convoluted tubule, the connecting tubule, and finally the straight collecting tubule, which opens at the apex of a renal papilla. The straight collecting tubules converge as they descend, forming groups in the center, known as medullary rays. See also Plate 20.


Medical dictionary. 2011.

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