Kidney 17025 225247102 2008-07-12T17:56:55Z Mansavian 7451179 /* Hormone secretion */ renin is an enzyme not a hormone {{Refimprove|date=June 2008}}{{Infobox Anatomy | Name = Kidney | Latin = ren | GraySubject = 253 | GrayPage = 1215 | Image = Kidneys_from_behind.jpg | Caption = Human kidneys viewed from behind with spine removed | Image2 = | Caption2 = System = | Artery = [[renal artery]] | Vein = [[renal vein]] | Nerve = [[renal plexus]] | Lymph = | MeshName = Kidney | MeshNumber = A05.810.453 | DorlandsPre = k_03 | DorlandsSuf = 12470097 }} The '''kidneys''' are complicated [[Organ (anatomy)| organs]] that have numerous biological roles. Their primary role is to maintain the [[homeostasis|homeostatic]] balance of bodily fluids by filtering and secreting [[Metabolomics#Metabolites| metabolite]]s (such as [[urea]]) and minerals from the [[blood]] and [[excreting]] them, along with [[water (molecule)|water]], as [[urine]]. Because the kidneys are poised to sense [[blood plasma|plasma]] concentrations of [[ion]]s such as [[sodium]], [[potassium]], [[hydrogen]], [[oxygen]], and compounds such as [[amino acids]], [[creatine]], [[bicarbonate]], and [[glucose]], they are important regulators of [[blood pressure]], glucose [[metabolism]], and [[erythropoiesis]] (the process by which [[red blood cells]] (erythrocytes) are produced). The medical field that studies the kidneys and [[diseases]] of the kidney is called [[nephrology]]<ref>{{cite web|url=http://dictionary.reference.com/browse/Nephrology|title=Nephrology|publisher=Dictionary.com |accessdate=2007-08-04}}</ref>. The prefix ''nephro-'' meaning kidney is from the [[Ancient Greek]] word ''nephros (νεφρός)''; the [[adjective]] ''renal'' meaning related to the kidney is from [[Latin]] ''rēnēs'', meaning kidneys. <ref>{{cite book | last = Maton | first = Anthea | authorlink = | coauthors = Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright | title = Human Biology and Health | publisher = Prentice Hall | date = 1993 | location = Englewood Cliffs, New Jersey, USA | pages = | url = | doi = | id = | isbn = 0-13-981176-1}}</ref> In [[human]]s, the kidneys are located in the [[posterior]] part of the [[abdomen]]. There is one on each side of the [[spine (anatomy)| spine]]; the right kidney sits just below the [[liver]], the left below the [[diaphragm (anatomy)| diaphragm]] and adjacent to the [[spleen]]. Above each kidney is an [[adrenal gland]] (also called the ''suprarenal gland''). The asymmetry within the abdominal cavity caused by the liver results in the right kidney being slightly lower than the left one while the left kidney is located slightly more medial. The kidneys are [[retroperitoneal]] and range from 9 to 13 cm in diameter; the left slightly larger than the right. They are approximately at the [[vertebra]]l level T12 to L3. The upper parts of the kidneys are partially protected by the eleventh and twelfth [[rib]]s, and each whole kidney and [[adrenal gland]] are surrounded by two layers of fat (the perirenal and pararenal fat) and the [[renal fascia]] which help to cushion it. Congenital absence of one or both kidneys, known as unilateral (on one side) or bilateral (on both the sides) [[renal agenesis]], can occur. ==Functions== {{main|Renal physiology}} ===Excretion of waste products=== The kidneys excrete a variety of waste products produced by [[metabolism]], including the nitrogenous wastes: [[urea]] (from protein catabolism) and [[uric acid]] (from nucleic acid metabolism) and water. ===Homeostasis=== The kidney is one of the major organs involved in whole-body [[homeostasis]]. Among its homeostatic functions are acid-base balance, regulation of [[electrolyte]] concentrations, control of [[blood volume]], and regulation of [[blood pressure]]. The kidneys accomplish these homeostatic functions independently and through coordination with other organs, particularly those of the [[endocrine system]]. The kidney communicates with these organs through hormones secreted into the bloodstream. ====Acid-base balance==== The kidneys regulate the [[pH]] of blood by adjusting H<sup>+</sup> ion levels, referred as augmentation of mineral ion concentration, as well as water composition of the blood. ====Blood pressure==== {{main|Renin-angiotensin system}} Sodium ions are controlled in a homeostatic process involving [[aldosterone]] which increases sodium ion reabsorption in the distal convoluted tubules. ====Plasma volume==== Any significant rise or drop in [[plasma osmolality]] is detected by the [[hypothalamus]], which communicates directly with the [[posterior pituitary gland]]. A rise in osmolality causes the gland to secrete [[antidiuretic hormone]], resulting in water reabsorption by the kidney and an increase in urine concentration. The two factors work together to return the plasma osmolality to its normal levels. ===Hormone secretion=== The kidneys secrete a variety of [[hormones]], including [[erythropoietin]], [[urodilatin]], and [[vitamin D]]. ==Embryology== {{Main|Development of the urinary and reproductive organs}} The mammalian kidney develops from [[intermediate mesoderm]]. Kidney development, also called ''nephrogenesis'', proceeds through a series of three successive phases, each marked by the development of a more advanced pair of kidneys: the pronephros, mesonephros, and metanephros.<ref>{{cite book | author = Bruce M. Carlson | title = Human Embryology and Developmental Biology | publisher = Mosby | location = Saint Louis | edition = 3rd edition | year = 2004 | id = ISBN 0-323-03649-X}}</ref> (The plural forms of these terms end in ''-oi''.) ===Pronephros=== {{Main|Pronephros}} During approximately day 22 of human [[gestation]], the paired pronephroi appear towards the cranial end of the intermediate mesoderm. In this region, [[epithelium|epithelial]] cells arrange themselves in a series of tubules called [[nephrotome]]s and join laterally with the [[pronephric duct]], which does not reach the outside of the embryo. Thus the pronephros is considered nonfunctional in mammals because it cannot excrete waste from the embryo. ===Mesonephros=== {{Main|Mesonephros}} Each pronephric duct grows towards the tail of the embryo, and in doing so induces intermediate mesoderm in the thoracolumbar area to become epithelial tubules called [[mesonephric tubule]]s. Each mesonephric tubule receives a blood supply from a branch of the [[aorta]], ending in a capillary tuft analogous to the [[glomerulus (kidney)|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 [[amphibian|aquatic amphibian]]s and [[fish]]es. ===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, 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 [[renal calyx|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 tubule]]s. As the renal tubules grow, they come into contact and join with [[connecting tubule]]s 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 (kidney)|glomerulus]]. ==Terms== [[Image:Kidney-Cortex.JPG|thumb|Microscopic photograph of the [[renal cortex]].]] [[Image:Kidney-medulla.JPG|thumb|Microscopic photograph of the [[renal medulla]].]] *'''[[renal capsule]]''': The membranous covering of the kidney. *'''[[cortex (anatomy)|cortex]]''': The outer layer over the internal medulla. It contains blood vessels, glomeruli (which are the kidneys' "filters") and [[urine]] tubes and is supported by a fibrous matrix. *'''[[hilus]]''': The opening in the middle of the concave medial border for nerves and blood vessels to pass into the renal sinus. *'''[[renal column]]''': The structures which support the cortex. They consist of lines of blood vessels and urinary tubes and a fibrous material. *'''[[renal sinus]]''': The cavity which houses the renal pyramids. *'''[[calyx (kidney)|calyces]]''': The recesses in the internal medulla which hold the pyramids. They are used to subdivide the sections of the kidney. (singular - ''calyx'') *'''[[wiktionary:Papillae|papillae]]''': The small conical projections along the wall of the [[renal sinus]]. They have openings through which urine passes into the calyces. (singular - [[Renal papilla|papilla]]) *'''[[renal pyramids]]''': The conical segments within the internal medulla. They contain the secreting apparatus and tubules and are also called ''[[malpighian pyramid]]s''. *'''[[renal artery]]''': Two renal arteries come from the [[aorta]], each connecting to a kidney. The artery divides into five branches, each of which leads to a ball of capillaries. The arteries supply (unfiltered) blood to the kidneys. The left kidney receives about 60% of the renal bloodflow. *'''[[renal vein]]''': The filtered blood returns to circulation through the renal veins which join into the [[inferior vena cava]]. *'''[[renal pelvis]]''': Basically just a [[funnel]], the renal pelvis accepts the urine and channels it out of the hilus into the [[ureter]]. *'''[[ureter]]''': A narrow tube 40 cm long and 4 mm in diameter. Passing from the renal pelvis out of the hilus and down to the [[urinary bladder|bladder]]. The ureter carries urine from the kidneys to the [[urinary bladder|bladder]] by means of [[peristalsis]]. *'''[[renal lobe]]''': Each pyramid together with the associated overlying cortex forms a renal lobe ==Diseases and disorders== ===Congenital=== *[[Congenital hydronephrosis]] *[[Congenital obstruction of urinary tract]] *[[Duplicated ureter]] *[[Horseshoe kidney]] *[[Polycystic kidney disease]] *[[Renal dysplasia]] *[[Unilateral small kidney]] *[[Multicystic dysplastic kidney]] ===Acquired=== [[Image:Hunter enlarged kidney.jpg|thumb|drawing of an enlarged kidney by [[John Hunter (surgeon)|John Hunter]]]] *[[Diabetic nephropathy]] *[[Glomerulonephritis]] *[[Hydronephrosis]] is the enlargement of one or both of the kidneys caused by obstruction of the flow of urine. *[[Interstitial nephritis]] *[[Kidney stone]]s are a relatively common and particularly painful disorder. *Kidney tumors **[[Wilms tumor]] **[[Renal cell carcinoma]] *[[Lupus nephritis]] *[[Minimal change disease]] *In [[nephrotic syndrome]], the [[glomerulus (kidney)|glomerulus]] has been damaged so that a large amount of [[protein]] in the blood enters the [[urine]]. Other frequent features of the nephrotic syndrome include swelling, low serum albumin, and high cholesterol. *[[Pyelonephritis]] is infection of the kidneys and is frequently caused by complication of a [[urinary tract infection]]. *[[Renal failure]] ** [[Acute renal failure]] ** [[Chronic kidney disease|Stage 5 Chronic Kidney Disease]] ==The failing kidney== Generally, humans can live normally with just one kidney, as one has more functioning renal tissue than is needed to survive. Only when the amount of functioning kidney tissue is greatly diminished will [[Chronic kidney disease|Stage 5 Chronic Kidney Disease]] develop. If the [[glomerular filtration rate]] (a measure of renal function) has fallen very low ( [[Chronic kidney disease|Stage 5 Chronic Kidney Disease]]), or if the renal dysfunction leads to severe symptoms, then [[renal replacement therapy]] is indicated, either [[dialysis]] or [[kidney transplantation]]. ==Medical terminology== * Medical terms related to the kidneys involve the prefixes ''renal-'' and ''nephro-''. * Surgical removal of the kidney is a ''[[nephrectomy]]'', while a ''radical nephrectomy'' is removal of the kidney, its surrounding tissue, lymph nodes, and potentially the adrenal gland. A radical nephrectomy is performed for the removal of the [[cancer]]s. ==Histology==<!--Interstitial kidney cell redirects here--> [[Human cell types]] found in the kidney include: *[[Kidney glomerulus parietal cell]] *[[Kidney glomerulus podocyte]] *[[Kidney proximal tubule brush border cell]] *[[Loop of Henle thin segment cell]] *[[Thick ascending limb]] cell *[[Kidney distal tubule cell]] *[[Kidney collecting duct cell]] **[[Cortical collecting duct]] cell **[[Medullary collecting duct]] cell *Interstitial kidney cell, which do not participate in the filtration process.<ref>[http://mednote.co.kr/14CYTOHISTO.htm mednote.co]</ref> ==Animal kidneys as food== The kidneys of animals can be [[cooking|cooked]] and eaten by humans (along with other [[offal]]). If prepared properly, they can be nutritious and pleasant tasting. Veal kidneys and lamb kidneys are particularly prized for their tenderness and flavour. Kidneys can be grilled or sautéed, though they become tough and unpleasant if overcooked. <!-- I see no research which indicates this. If put back in, this requires a reputable source: Kidneys of dogs are known to be toxic to humans (especially from elderly dogs).{{Fact|date=August 2007}} --> ==See also== *[[Kidney stone]] *[[Kidney transplantation]] *[[Renal physiology]] *[[Urinary system]] ==References== {{Nofootnotes|date=June 2008}} {{commonscat}} {{reflist}} ==External links== *[http://www.uni-mainz.de/FB/Medizin/Anatomie/workshop/EM/EMNiereE.html electron microscopic images of the kidney (Dr. Jastrow's EM-Atlas)] *[http://www.euregene.org/euregene/pages/kidney_tut_e.html European Renal Genome project kidney function tutorial] *[http://www.kidneyquebec.ca/ang/kidney_disease/index.htm Kidney Foundation of Canada kidney disease information] *[http://www.kidney.org National Kidney Foundation] *[http://www.kidney.ca Kidney Foundation (Canada)] *[http://www.bcrenalagency.ca BC Renal Agency] - Official site for the province-wide network of renal care providers in [[British Columbia]], [[Canada]] *[http://www.worldkidneyday.org World Kidney Day website] *[http://www.uncnephropathology.org UNC Nephropathology] *[http://www.kidney-renal-disease.info Information on kidneys] {{kidney}} {{urinary system}} [[Category:Organs]] [[Category:Abdomen]] [[Category:Endocrine system]] [[Category:Kidney| ]] [[af:Nier]] [[ar:كلية]] [[bn:বৃক্ক]] [[bs:Bubreg]] [[bg:Бъбрек]] [[ca:Ronyó]] [[cv:Пӳре]] [[cs:Ledvina]] [[cy:Aren]] [[da:Nyre]] [[de:Niere]] [[dv:ގުރުދާ]] [[et:Neerud]] [[es:Riñón]] [[eo:Reno]] [[eu:Giltzurrun]] [[fa:کلیه]] [[fr:Rein]] [[gl:Ril]] [[ko:콩팥]] [[hr:Bubrezi]] [[id:Ginjal]] [[is:Nýra]] [[it:Rene]] [[he:כליה]] [[pam:Batu]] [[ku:Gurçik]] [[la:Ren]] [[lv:Nieres]] [[lt:Inkstas]] [[hu:Vese]] [[ml:വൃക്ക]] [[mt:Kilwa]] [[ms:Buah pinggang]] [[nl:Nier (biologie)]] [[ja:腎臓]] [[no:Nyre]] [[nn:Nyre]] [[pag:Batok]] [[pl:Nerka]] [[pt:Rim]] [[ro:Rinichi]] [[qu:Wasa ruru]] [[ru:Почка (анатомия)]] [[scn:Rini]] [[simple:Kidney]] [[sk:Oblička]] [[sl:Ledvica]] [[sr:Бубрег]] [[sh:Bubreg]] [[su:Ginjal]] [[fi:Munuainen]] [[sv:Njure]] [[ta:சிறுநீரகம்]] [[te:మూత్రపిండము]] [[th:ไต]] [[tr:Böbrek]] [[uk:Нирки]] [[ur:كُلیَہ]] [[fiu-vro:Rauh]] [[yi:ניער]] [[zh:腎]]