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{{short description|
{{Other uses}}
{{pp-semi-indef}}
{{Infobox anatomy
| Name = Kidneys
| Latin =
| Greek =
| Image = Blausen 0592 KidneyAnatomy 01.png
| Caption = The kidneys lie in the [[retroperitoneal space]] behind the abdomen, and act to filter blood to create [[urine]]
| Image2 = Gray1123.png
| Caption2 = View of the kidneys from behind, showing their blood supply and drainage
| Precursor =
| System = [[Urinary system]] and [[endocrine system]]
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}}
The kidney participates in the control of the volume of various [[body fluid]]s, fluid [[osmolality]], [[
[[Chronic kidney disease]] (CKD) has been recognized as a leading public health problem worldwide. The global estimated prevalence of CKD is 13.4%, and patients with [[kidney failure]] needing [[renal replacement therapy]] are estimated between 5 and 7 million.<ref name="Ji Cheng">{{cite
[[Renal physiology]] is the study of [[kidney function]]. [[Nephrology]] is the medical specialty which addresses diseases of kidney ''function'':
The word “[[wikt:renal|renal]]” is an adjective meaning “relating to the kidneys”, and its roots are French or late Latin. Whereas according to some opinions, "renal" should be replaced with "kidney" in scientific writings such as "kidney artery", other experts have advocated preserving the use of {{TOC limit|3}}
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== Structure ==
[[File:Surface projections of the organs of the trunk.png|thumb|300px|Image showing the human [[trunk (anatomy)|trunk]] with positions of the organs. The kidneys are at the [[vertebral level]] of T12 to L3. ]]
In humans, the kidneys are located high in the [[abdominal cavity]], one on each side of the [[vertebral column|spine]], and lie in a [[retroperitoneal]] position at a slightly oblique angle.<ref>{{cite web
The human kidney is a bean-shaped structure with a [[wikt:convex|convex]] and a [[wikt:concave|concave]] border.<ref>{{Cite web |title=Renal system |url=https://www.britannica.com/science/human-renal-system |access-date=2022-05-22 |website=Britannica |language=en |archive-date=2022-05-31 |archive-url=https://web.archive.org/web/20220531015045/https://www.britannica.com/science/human-renal-system |url-status=live }}</ref> A recessed area on the concave border is the [[renal hilum]], where the [[renal artery]] enters the kidney and the [[renal vein]] and [[ureter]] leave. The kidney is surrounded by tough fibrous tissue, the [[renal capsule]], which is itself surrounded by [[adipose capsule of kidney|perirenal fat]], [[renal fascia]], and [[pararenal fat]]. The anterior (front) surface of these tissues is the [[peritoneum]], while the posterior (rear) surface is the [[transversalis fascia]].
The superior pole of the right kidney is adjacent to the liver. For the left kidney, it is next to the [[spleen]]. Both, therefore, move down upon inhalation.
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|align="center"| '''Right kidney''' ||align="center"| '''Left kidney'''
|-
| Male<ref name="MolinaDiMaio2012">{{cite journal | vauthors = Molina DK, DiMaio VJ | title = Normal organ weights in men: part II
|-
| Female<ref name="MolinaDiMaio2015">{{cite journal | vauthors = Molina DK, DiMaio VJ | title = Normal Organ Weights in Women: Part II-The Brain, Lungs, Liver, Spleen, and Kidneys | journal = The American Journal of Forensic Medicine and Pathology | volume = 36 | issue = 3 | pages = 182–187 | date = September 2015 | pmid = 26108038 | doi = 10.1097/PAF.0000000000000175 | s2cid = 25319215 }}</ref> || {{convert|40-175|g|oz|frac=4|abbr=on}} || {{convert|35-190|g|oz|frac=4|abbr=on}}
|}
A Danish study measured the median renal length to be {{convert|11.2|cm|in|frac=16|abbr=on}} on the left side and {{convert|10.9|cm|in|frac=16|abbr=on}} on the right side in adults. Median renal volumes were {{cvt|146|cm3|cuin|frac=16}} on the left and {{cvt|134|cm3|cuin|frac=16}} on the right.<ref>{{cite journal | vauthors = Emamian SA, Nielsen MB, Pedersen JF, Ytte L | title = Kidney dimensions at sonography: correlation with age, sex, and habitus in 665 adult volunteers | journal = AJR. American Journal of Roentgenology | volume = 160 | issue = 1 | pages = 83–86 | date = January 1993 | pmid = 8416654 | doi = 10.2214/ajr.160.1.8416654 | doi-access =
===Gross anatomy===
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17. [[Renal column]]
</div>]]
The functional substance, or [[Parenchyma#Renal parenchyma|parenchyma]], of the human kidney is divided into two major structures: the outer [[renal cortex]] and the inner [[renal medulla]]. Grossly, these structures take the shape of eight to 18 cone-shaped [[renal lobe]]s, each containing renal cortex surrounding a portion of medulla called a [[renal pyramid]].<ref name="boron">{{cite book | vauthors = Boron WF |title=Medical Physiology: A Cellular And Molecular Approach |publisher=Elsevier/Saunders |year=2004 |isbn=978-1-4160-2328-9 }}</ref> Between the renal pyramids are projections of cortex called [[renal column]]s
The tip, or [[renal papilla|papilla]], of each pyramid empties urine into a [[minor calyx]]; minor calyces empty into [[major calyces]], and major calyces empty into the [[renal pelvis]]. This becomes the ureter. At the hilum, the ureter and renal vein exit the kidney and the renal artery enters. Hilar fat and lymphatic tissue with lymph nodes surround these structures. The hilar fat is contiguous with a fat-filled cavity called the [[renal sinus]]. The renal sinus collectively contains the renal pelvis and calyces and separates these structures from the renal medullary tissue.<ref>{{cite book | vauthors = Clapp WL | chapter = Renal Anatomy | veditors = Zhou XJ, Laszik Z, Nadasdy T, D'Agati VD, Silva FG | title = Silva's Diagnostic Renal Pathology | location = New York| publisher = Cambridge University Press | date = 2009 | isbn = 978-0-521-87702-2 }}</ref>
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<gallery mode="packed">
File:Right kidney seen on abdominal ultrasound.jpg
File:CTscankidney.jpg|A [[CT scan]] of the abdomen showing the position of the kidneys. The left cross-section in the upper abdomen shows the [[liver]] on the left side of scan (right side of body). Center: cross-section showing the kidneys below the liver and spleen. Right: further cross-section through the left kidney.
File:Slide42222.JPG|Image showing the structures that the kidney lies near
File:Left kidney.jpg|Cross-section through a [[cadaver]]ic specimen showing the position of the kidneys
</gallery>
=== Blood supply ===
{{main|Renal circulation}}
The kidneys receive blood from the [[renal artery|renal arteries]], left and right, which branch directly from the [[abdominal aorta]]. The kidneys receive approximately 20–25% of [[cardiac output]] in adult human.<ref name="boron"/><ref>{{Citation |title=Urinary system |date=2015 |url=https://www.cambridge.org/core/books/design-of-mammals/urinary-system/E76848B86DA00C151DA92EDD8AB2F418 |work=The Design of Mammals: A Scaling Approach |pages=195–203 |editor-last=Prothero |editor-first=John William |place=Cambridge |publisher=Cambridge University Press |doi=10.1017/CBO9781316275108.016 |isbn=978-1-107-11047-2 |access-date=2022-06-25 |archive-date=2018-06-17 |archive-url=https://web.archive.org/web/20180617094738/https://www.cambridge.org/core/books/design-of-mammals/urinary-system/E76848B86DA00C151DA92EDD8AB2F418 |url-status=live }}</ref><ref>{{Cite book |last1=Martini |first1=Frederic |title=Human Anatomy |last2=Tallitsch |first2=Robert B. |last3=Nath |first3=Judi L. |publisher=Pearson |year=2017 |isbn=9780134320762 |edition=9th |pages=689}}</ref> Each renal artery branches into segmental arteries, dividing further into [[interlobar arteries]], which penetrate the renal capsule and extend through the renal columns between the renal pyramids. The interlobar arteries then supply blood to the [[arcuate arteries]] that run through the boundary of the cortex and the medulla. Each arcuate artery supplies several [[interlobular]] arteries that feed into the [[afferent arteriole]]s that supply the glomeruli.
Blood drains from the kidneys, ultimately into the [[inferior vena cava]]. After filtration occurs, the blood moves through a small network of small veins ([[venules]]) that converge into [[interlobular veins]]. As with the arteriole distribution, the veins follow the same pattern: the interlobular provide blood to the [[arcuate veins]] then back to the [[interlobar veins]], which come to form the [[renal vein]]s which exit the kidney.
===Nerve supply===
The kidney and [[nervous system]] communicate via the [[renal plexus]], whose fibers course along the renal arteries to reach each kidney.<ref name="Bard">{{cite book |
=== Microanatomy ===
Renal [[histology]] is the study of the [[microscopic]] structure of the kidney. Distinct [[cell type]]s include:▼
{{citation needed span|date=November 2023|[[Nephron]]s, the urine-producing functional structures of the kidney, span the cortex and medulla. The initial filtering portion of a nephron is the [[renal corpuscle]], which is located in the cortex. This is followed by a [[renal tubule]] that passes from the cortex deep into the medullary pyramids. Part of the renal cortex, a [[medullary ray (anatomy)|medullary ray]] is a collection of renal tubules that drain into a single [[collecting duct]].}}
▲Renal [[histology]] is the study of the [[microscopic]] structure of the kidney.
*Kidney glomerulus parietal cell
*[[Kidney glomerulus podocyte]]
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== Gene and protein expression ==
{{Further |Bioinformatics#Gene and protein expression}}
In humans, about 20,000 protein coding genes are expressed in human cells and almost 70% of these genes are expressed in normal, adult kidneys.<ref>{{Cite web|url=https://www.proteinatlas.org/humanproteome/kidney|title=The human proteome in kidney – The Human Protein Atlas|website=www.proteinatlas.org|access-date=2017-09-22|archive-date=2017-09-22|archive-url=https://web.archive.org/web/20170922194202/https://www.proteinatlas.org/humanproteome/kidney|url-status=live}}</ref><ref>{{cite journal | vauthors = Uhlén M, Fagerberg L, Hallström BM, Lindskog C, Oksvold P, Mardinoglu A, Sivertsson Å, Kampf C, Sjöstedt E, Asplund A, Olsson I, Edlund K, Lundberg E, Navani S, Szigyarto CA, Odeberg J, Djureinovic D, Takanen JO, Hober S, Alm T, Edqvist PH, Berling H, Tegel H, Mulder J, Rockberg J, Nilsson P, Schwenk JM, Hamsten M, von Feilitzen K, Forsberg M, Persson L, Johansson F, Zwahlen M, von Heijne G, Nielsen J, Pontén F | display-authors = 6 | title = Proteomics. Tissue-based map of the human proteome | journal = Science | volume = 347 | issue = 6220 | pages = 1260419 | date = January 2015 | pmid = 25613900 | doi = 10.1126/science.1260419 | s2cid = 802377 }}</ref> Just over 300 genes are more specifically expressed in the kidney, with only some 50 genes being highly specific for the kidney. Many of the corresponding kidney specific proteins are expressed in the cell membrane and function as transporter proteins. The highest expressed kidney specific protein is [[Tamm–Horsfall protein|uromodulin]], the most abundant protein in urine with functions that prevent calcification and growth of bacteria. Specific proteins are expressed in the different compartments of the kidney with [[podocin]] and [[nephrin]] expressed in glomeruli,
== Development ==
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{{main|Renal physiology}}
The kidneys excrete a variety of waste products produced by [[metabolism]] into the urine. The microscopic structural and functional unit of the kidney is the [[nephron]]. It processes the blood supplied to it via filtration, reabsorption, secretion and excretion; the consequence of those processes is the production of [[urine]]. These include the nitrogenous wastes [[urea]], from protein [[catabolism]], and [[uric acid]], from [[nucleic acid]] metabolism.
The kidney participates in whole-body [[homeostasis]], regulating [[
===Formation of urine===
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====Filtration====
Filtration, which takes place at the [[renal corpuscle]], is the process by which cells and large proteins are retained while materials of smaller molecular weights are<ref>{{cite book | vauthors = Hall JE |title=Guyton and Hall textbook of medical physiology |date=2016 |publisher=Elsevier Health Sciences |location=Philadelphia, PA |isbn=978-0-323-38930-3 |edition=13th | page = 1129 }}</ref> filtered from the blood to make an [[Ultrafiltration (kidney)|ultrafiltrate]] that eventually becomes urine. The adult human kidney generates approximately 180 liters of filtrate a day, most of which is reabsorbed.<ref>{{Cite book |last1=Alpern |first1=Robert J. |url=https://books.google.com/books?id=w5nEg7VLEQ4C&pg=1405 |title=Seldin and Giebisch's The Kidney: Physiology and Pathophysiology |last2=Caplan |first2=Michael |last3=Moe |first3=Orson W. |date=2012-12-31 |publisher=Academic Press |isbn=978-0-12-381463-0 |pages=1405 |language=en |access-date=2022-07-28 |archive-date=2023-07-22 |archive-url=https://web.archive.org/web/20230722105802/https://books.google.com/books?id=w5nEg7VLEQ4C&pg=1405 |url-status=live }}</ref> The normal range for a twenty four hour urine volume collection is 800 to 2,000 milliliters per day.<ref>{{cite web
====Reabsorption====
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==== Excretion ====
The last step in the processing of the ultrafiltrate is ''excretion'': the ultrafiltrate passes out of the nephron and travels through a tube called the ''collecting duct'', which is part of the [[collecting duct system]], and then to the ureters where it is renamed
===Hormone secretion===
The kidneys secrete a variety of [[hormones]], including [[erythropoietin]], [[calcitriol]], and [[renin]]. [[Erythropoietin]] is released in response to [[Hypoxia (medical)|hypoxia]] (low levels of oxygen at tissue level) in the renal circulation. It stimulates [[erythropoiesis]] (production of red blood cells) in the [[bone marrow]]. [[Calcitriol]], the activated form of [[vitamin D]], promotes intestinal absorption of [[calcium]] and the renal [[reabsorption]] of [[phosphate]].
===Blood pressure regulation===
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{{main|Acid–base homeostasis}}
The two organ systems that help regulate the body's
The kidneys have two cells that help to maintain acid-base homeostasis: intercalated A and B cells. The intercalated A cells are stimulated when the body is experiencing acidic conditions. Under acidic conditions, the high concentration of
=== Regulation of osmolality ===
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Medical terms related to the kidneys commonly use terms such as ''renal'' and the prefix ''nephro-''. The [[adjective]] ''renal'', meaning related to the kidney, is from the [[Latin language|Latin]] ''rēnēs'', meaning kidneys; the prefix ''nephro-'' is from the [[Ancient Greek]] word for kidney, ''nephros (νεφρός)''.<ref>{{cite book | vauthors = Maton A, Hopkins J, McLaughlin CW, Johnson S, Warner MQ, LaHart D, Wright JD | title = Human Biology and Health | publisher = Prentice Hall | year = 1993 | location = Englewood Cliffs, New Jersey, USA | url = https://archive.org/details/humanbiologyheal00scho | isbn = 978-0-13-981176-0 | url-access = registration }}</ref> For example, surgical removal of the kidney is a ''[[nephrectomy]]'', while a reduction in kidney function is called ''renal dysfunction''.
===Acquired Disease===
*[[Diabetic nephropathy]]
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{{main|Acute kidney injury|Chronic kidney disease|Kidney failure}}
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 does one develop [[chronic kidney disease]]. [[Renal replacement therapy]], in the form of [[Kidney dialysis|dialysis]] or [[kidney transplantation]], is indicated when the [[glomerular filtration rate]] has fallen very low or if the renal dysfunction leads to severe symptoms.<ref>{{cite journal | vauthors = Kalantar-Zadeh K, Jafar TH, Nitsch D, Neuen BL, Perkovic V | title = Chronic kidney disease | journal = Lancet | volume = 398 | issue = 10302 | pages = 786–802 | date = August 2021 | pmid = 34175022 | doi = 10.1016/S0140-6736(21)00519-5 | s2cid = 235631509 | url = https://researchonline.lshtm.ac.uk/id/eprint/4663580/1/Kalantar-Zadeh_etal_2021-Preserving-Kidney-Function-in-People.pdf | access-date = 2022-05-22 | archive-date = 2022-05-17 | archive-url = https://web.archive.org/web/20220517153016/https://researchonline.lshtm.ac.uk/id/eprint/4663580/1/Kalantar-Zadeh_etal_2021-Preserving-Kidney-Function-in-People.pdf | url-status = live }}</ref>
===Dialysis===
[[File:Peritoneal dialysis.jpg|thumb|258x258px|A depiction of [[peritoneal dialysis]]
{{main|Kidney dialysis}}
Dialysis is a treatment that substitutes for the function of normal kidneys. Dialysis may be instituted when approximately 85%
===Congenital disease===
*Congenital [[hydronephrosis]]
*Congenital obstruction of urinary tract
*Duplex kidneys, or double kidneys, occur in approximately 1% of the population. This occurrence normally causes no complications, but can occasionally cause urinary tract infections.<ref>{{cite news |url=https://www.theguardian.com/society/2008/feb/19/health |title=How many people have four kidneys? |work=
*[[Duplicated ureter]] occurs in approximately one in 100 live births
*[[Horseshoe kidney]] occurs in approximately one in 400 live births
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*Unilateral small kidney
*[[Multicystic dysplastic kidney]] occurs in approximately one in every 2400 live births
*Ureteropelvic Junction Obstruction or UPJO; although most cases are congenital, some are acquired.<ref>{{Cite
=== Diagnosis ===
Many renal diseases are diagnosed on the basis of a detailed [[medical history]], and [[physical examination]].<ref>{{cite journal |
[[Renal function|Kidney function]] is tested by using [[blood test]]s and [[Clinical urine tests|urine tests]]. The most common blood tests are [[creatinine]], [[urea]] and [[electrolyte]]s. Urine tests such as [[urinalysis]] can evaluate for pH, protein, glucose, and the presence of blood. Microscopic analysis can also identify the presence of [[urinary cast]]s and crystals.<ref name="uptodate.com"/> The [[glomerular filtration rate]] (GFR) can be directly measured ("measured GFR", or mGFR) but this rarely done in everyday practice. Instead, special equations are used to calculate GFR ("estimated GFR", or eGFR).<ref>{{cite journal |title=KDIGO 2012 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease |journal=Kidney Int Suppl |date=2013 |volume=3 |pages=1–150 |url=https://kdigo.org/guidelines/ckd-evaluation-and-management/ |access-date=2021-01-25 |archive-date=2019-05-01 |archive-url=https://web.archive.org/web/20190501124111/https://kdigo.org/guidelines/ckd-evaluation-and-management/ |url-status=live }}</ref><ref name="uptodate.com">{{cite web|
==== Imaging ====
[[Renal ultrasonography]] is essential in the diagnosis and management of kidney-related diseases.<ref name=Hansen2015>Content initially copied from: {{cite journal | vauthors = Hansen KL, Nielsen MB, Ewertsen C | title = Ultrasonography of the Kidney: A Pictorial Review | journal = Diagnostics | volume = 6 | issue = 1 | pages = 2 | date = December 2015 | pmid = 26838799 | pmc = 4808817 | doi = 10.3390/diagnostics6010002 | doi-access = free }} [https://creativecommons.org/licenses/by/4.0/ (CC-BY 4.0)] {{Webarchive|url=https://web.archive.org/web/20171016050101/https://creativecommons.org/licenses/by/4.0/ |date=2017-10-16 }}</ref> Other modalities, such as [[CT scan|CT]] and [[magnetic resonance imaging|MRI]], should always be considered as supplementary imaging modalities in the assessment of renal disease.<ref name=Hansen2015/>
==== Biopsy ====
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====India: Ayurvedic system====
In ancient India, according to the [[Ayurveda|Ayurvedic medical systems]], the kidneys were considered the beginning of the excursion channels system, the 'head' of the ''Mutra Srota''s, receiving from all other systems, and therefore important in determining a person's health balance and temperament by the balance and mixture of the three 'Dosha's – the three health elements: Vatha (or Vata) – air, Pitta – [[bile]], and Kapha – [[mucus]]. The temperament and health of a person can then be seen in the resulting color of the urine.<ref>{{Cite web|url=http://www.ayurvedacollege.com/articles/drhalpern/Vata_Doshas|title=What is Vata Dosha? Tips and diet for balancing vata | CA College of Ayurveda|website=www.ayurvedacollege.com|date=7 April 2010|access-date=July 21, 2019|archive-date=9 November 2019|archive-url=https://web.archive.org/web/20191109092730/http://www.ayurvedacollege.com/articles/drhalpern/Vata_Doshas|url-status=live}}</ref>
Modern Ayurveda practitioners, a practice which is characterized as pseudoscience,<ref>[[List of topics characterized as pseudoscience]], according to the [[American Medical Association]]'s Report 12 of the Council of Scientific Affairs (A-97) and [http://www.skepdic.com/ayurvedic.html claims by skeptics] {{Webarchive|url=https://web.archive.org/web/20160810061129/http://skepdic.com/ayurvedic.html |date=2016-08-10 }} ('The Skeptics Dictionary' website)</ref> have attempted to revive these methods in medical procedures as part of Ayurveda [[Urine therapy]].<ref>{{cite journal | vauthors = Sangu PK, Kumar VM, Shekhar MS, Chagam MK, Goli PP, Tirupati PK | title = A study on Tailabindu pariksha
====Medieval Christianity====
The Latin term ''renes'' is related to the English word "reins", a synonym for the kidneys in [[Shakespearean English]] (e.g. ''[[Merry Wives of Windsor]]'' 3.5), which was also the time when the [[King James Version]] of the [[Bible]] was translated. Kidneys were once popularly regarded as the seat of the [[conscience]] and reflection,<ref>{{cite book |author3-link=William F. May (ethicist) | vauthors = Ramsey P, Jonsen AR, May WF |title=The Patient as Person: Explorations in Medical Ethics |date=2002 |publisher=Yale University Press |location=New Haven |isbn=978-0-300-09396-4 |page=60 |edition=Second}}</ref><ref>{{cite book |title=History of Nephrology 2 |date=January 1997 |publisher=Karger Medical and Scientific Publishers |isbn=978-3-8055-6499-1 | page = 235 | veditors = Eknoyan G, Marketos SG, De Santo NG }} International Association for the History of Nephrology Congress, Reprint of ''American Journal of Nephrology''; v. 14, no. 4–6, 1994.</ref> and a number of verses in the Bible (e.g. Ps. 7:9, Rev. 2:23) state that God searches out and inspects the kidneys, or "reins", of humans, together with the heart.<ref>{{citation |url=https://intertextual.bible/text/revelation-2.23-berakhot-119.29 |title=intertextual.bible/text/revelation-2.23-berakhot-119.29 |access-date=2022-12-15 |archive-date=2022-12-15 |archive-url=https://web.archive.org/web/20221215081525/https://intertextual.bible/text/revelation-2.23-berakhot-119.29 |url-status=live }}</ref>
==History==
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==Additional images==
<gallery>
File:Slide4nn.JPG|Right
File:Slide5pp.JPG|Kidney
File:Slide3ppp.JPG|Right
File:Right kidney.jpg|Right kidney
File:Left kidneys.jpg|Left kidney
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*[[Pelvic kidney]]
*[[World Kidney Day]]
*[[List of distinct cell types in the adult human body]]
== References ==
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{{Commons category|Kidneys}}
* [https://www.proteinatlas.org/humanproteome/kidney Kidney at the Human Protein Atlas]
* [http://www.uni-mainz.de/FB/Medizin/Anatomie/workshop/EM/EMNiereE.html
{{Urinary system anatomy}}
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