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Kidney

The kidneys are two bean-shaped organs found on the left and right sides of the body in vertebrates. They are located at the back of the abdominal cavity in the retroperitoneal space. They are about in length.They receive blood from the paired renal arteries; blood exits into the paired renal veins. Each kidney has an excretory tube, the ureter, which ends at the bladder. Microscopically, the basic structural and functional unit of the kidney is the nephron: its structure resembles the letter "S" turned on its side. The nephron and its associated peritubular capillary carry out four basic functions: filtration, reabsorption, secretion, and excretion. Filtration occurs in the glomerulus: all blood components are filtered except blood cells and blood proteins. One-fifth of the blood volume that enters the kidneys is filtered. Examples of substances reabsorbed are solute-free water, sodium, bicarbonate, glucose, and amino acids. Examples of substances secreted are potassium and uric acid. Examples of substances excreted are urea, ammonium, and uric acid. The kidneys also carry out functions not part of the nephron. For example, they convert a precursor to produce calcitriol, and synthesize the hormones erythropoietin and renin. Renal physiology is the study of kidney function. Nephrology is the medical speciality which addresses kidney function diseases. These include nephritic and nephrotic syndromes, acute kidney injury, chronic kidney disease including dialysis management, and urinary tract infection. Urology addresses abnormal kidney (and urinary tract) anatomy, such as renal cysts, kidney stones, urinary tract obstruction, renal carcinoma, and renal transplantation.

Structure

Location

, showing kidneys at the level of T12 to L3. ]] In humans, the kidneys are located high in the abdominal cavity, one on each side of the spine, and lie in a retroperitoneal position at a slightly oblique angle. The asymmetry within the abdominal cavity, caused by the position of the liver, typically results in the right kidney being slightly lower and smaller than the left, and being placed slightly more to the middle than the left kidney. The left kidney is approximately at the vertebral level T12 to L3,Bålens ytanatomy (Superficial anatomy of the trunk). Anca Dragomir, Mats Hjortberg and Godfried M. Romans. Section for human anatomy at the Department of Medical Biology, Uppsala University, Sweden. and the right is slightly lower. The right kidney sits just below the diaphragm and posterior to the liver. The left sits below the diaphragm and posterior to the spleen. On top of each kidney is an adrenal gland. The upper parts of the kidneys are partially protected by the 11th and 12th ribs. Each kidney, with its adrenal gland is surrounded by two layers of fat: the perinephric fat present between renal fascia and renal capsule and paranephric fat superior to the renal fascia.

Structure

[[File:KidneyStructures PioM.svg|thumb|300px|right| 1.  Renal pyramid • 2.  Interlobular artery • 3.  Renal artery • 4.  Renal vein 5.  Renal hilum • 6.  Renal pelvis • 7.  Ureter • 8.  Minor calyx • 9.  Renal capsule • 10.  Inferior renal capsule • 11.  Superior renal capsule • 12.  Interlobular vein • 13.  Nephron • 14.  Renal sinus • 15.  Major calyx • 16.  Renal papilla • 17.  Renal column ]] The kidney is a bean-shaped structure with a and a border. 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 perirenal fat ( adipose capsule), renal fascia, and pararenal fat ( paranephric body). 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. In adult males, the kidney weighs between 125 and 170 grams. In females the weight of the kidney is between 115 and 155 grams. A Danish study measured the median renal length to be on the left side and on the right side in adults. Median renal volumes were 146 cm3 on the left and 134 cm3 on the right. The substance, or parenchyma, of the 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 lobes, each containing renal cortex surrounding a portion of medulla called a renal pyramid (of Malpighi). Between the renal pyramids are projections of cortex called renal columns (or Bertin columns). Nephrons, 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 is a collection of renal tubules that drain into a single collecting duct. The tip, or 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 surrounds 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.Clapp, WL. "Renal Anatomy". In: Zhou XJ, Laszik Z, Nadasdy T, D'Agati VD, Silva FG, eds. Silva's Diagnostic Renal Pathology. New York: Cambridge University Press; 2009. The kidneys possess no overtly moving structures

Blood supply

, showing renal arteries and veins.]] The renal circulation supplies the blood to the kidneys via the renal arteries, left and right, which branch directly from the abdominal aorta. Despite their relatively small size, the kidneys receive approximately 20% of the cardiac output. 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 arterioles that supply the glomeruli. The medullary interstitium is the functional space in the kidney beneath the individual filters (glomeruli), which are rich in blood vessels. The interstitium absorbs fluid recovered from urine. Various conditions can lead to scarring and of this area, which can cause kidney dysfunction and failure. After filtration occurs, the blood moves through a small network of 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 exiting the kidney for transfusion for blood. The table below shows the path that blood takes when it travels through the glomerulus, traveling "down" the arteries and "up" the veins. However, this model is greatly simplified for clarity and symmetry. Some of the other paths and complications are described at the bottom of the table. The interlobar artery and vein (not to be confused with interlobular) are between two renal lobes, also known as the renal column (cortex region between two pyramids).
  • Note 1: The renal artery also provides a branch to the inferior suprarenal artery to supply the adrenal gland.
  • Note 2: Each renal artery partitions into an anterior and posterior branch. The anterior branch further divides into the superior (apical), anterosuperior, anteroinferior and inferior segmental arteries. The posterior branch continues as the posterior segmental artery.
  • Note 3: Also called the cortical radiate arteries. The interlobular artery also supplies to the stellate veins.
  • Note 4: The efferent arterioles do not directly drain into the interlobular vein, but rather they go to the peritubular capillaries first. The efferent arterioles of the juxtamedullary nephron drain into the vasa recta.

Nerve supply

The kidney and nervous system communicate via the renal plexus, whose fibers course along the renal arteries to reach each kidney. Input from the sympathetic nervous system triggers vasoconstriction in the kidney, thereby reducing renal blood flow. The kidney also receives input from the parasympathetic nervous system, by way of the renal branches of the vagus nerve (cranial nerve X); the function of this is yet unclear. Sensory input from the kidney travels to the T10-11 levels of the spinal cord and is sensed in the corresponding dermatome. Thus, pain in the flank region may be referred from corresponding kidney.

Microanatomy

Normal human FF is 20%.

Renal clearance

Renal clearance is the volume of plasma from which the substance is completely cleared from the blood per unit time. (U'x)}}
  • is the clearance of X (normally in units of mL/min.
  • is the urine concentration of X.
  • is the plasma concentration of X.
  • is the urine flow rate.

Mathematical modelling

The kidney is a very complex organ and numerical modelling has been used to better understand kidney function at several scales, including fluid uptake and secretion.

Clinical significance

Kidney disease, is kidney disease or damage to a kidney. Nephrosis is non-inflammatory nephropathy and nephritis is inflammatory kidney disease. Nephrology is the speciality that deals with kidney function and disease. 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 rēnēs, meaning kidneys; the prefix nephro- is from the Ancient Greek word for kidney, nephros (νεφρός). For example, surgical removal of the kidney is a nephrectomy, while a reduction in kidney function is called renal dysfunction.

Acquired

Kidney injury and 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 dialysis or kidney transplantation, is indicated when the glomerular filtration rate has fallen very low or if the renal dysfunction leads to severe symptoms.

Dialysis

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 urine infections.
  • Duplicated ureter occurs in approximately one in 100 live births
  • Horseshoe kidney occurs in approximately one in 400 live births
  • Nutcracker syndrome
  • Polycystic kidney disease
  • * Autosomal dominant polycystic kidney disease afflicts patients later in life. Approximately one in 1000 people will develop this condition
  • * Autosomal recessive polycystic kidney disease is far less common, but more severe, than the dominant condition. It is apparent in utero or at birth.
  • Renal agenesis. Failure of one kidney to form occurs in approximately one in 750 live births. Failure of both kidneys to form used to be fatal; however, medical advances such as amnioinfusion therapy during pregnancy and peritoneal dialysis have made it possible to stay alive until a transplant can occur.
  • Renal dysplasia
  • Unilateral small kidney
  • Multicystic dysplastic kidney occurs in approximately one in every 2400 live births
  • Ureteropelvic Junction Obstruction or UPJO; although most cases appear congenital, some appear to be an acquired condition

Evaluation for disease

Patient encounter

Many renal diseases are diagnosed on the basis of a detailed clinical history and performance of a physical examination. Medication history, family history, recent infections, toxic/chemical exposures are relevant.

Blood tests

Blood tests are important to assess kidney function. These may include a full blood count, serum electrolytes including sodium, potassium, chloride, bicarbonate, calcium, and phosphorus; blood urea, nitrogen and creatinine; blood glucose and glycocylated hemoglobin. Glomerular filtration rate (GFR) can be calculated.Post TW, Rose BD, auths and Curhan GC, Sheridan AM, eds. Diagnostic Approach to the Patient With Acute Kidney Injury (Acute Renal Failure) or Chronic Kidney Disease. UpToDate.com, Dec. 2012. http://www.uptodate.com/contents/diagnostic-approach-to-the-patient-with-acute-kidney-injury-acute-renal-failure-or-chronic-kidney-disease?source=preview&anchor=H12&selectedTitle=1~150#H12

Urine tests

Urine studies may include urine electrolytes, creatinine, protein, fractional excretion of sodium (FENA) and other studies to assist in evaluation of the etiology of a patient's renal disease. Urinalysis is used to evaluate urine for its pH, protein, glucose, specific gravity and the presence of blood. Microscopic analysis can be helpful in the identification of casts, red blood cells, white blood cells and crystals.

Imaging

Imaging studies are important in the evaluation of structural renal disease caused by urinary tract obstruction, renal stones, renal cyst, mass lesions, renal vascular disease, and vesicoureteral reflux. Imaging techniques used most frequently include renal ultrasound and helical CT scan. Patients with suspected vesicoureteral reflux may undergo voiding cystourethrogram (VCUG).

Biopsy

The role of the renal biopsy is to diagnose renal disease in which the etiology is not clear based upon noninvasive means (clinical history, past medical history, medication history, physical exam, laboratory studies, imaging studies). In general, a renal pathologist will perform a detailed morphological evaluation and integrate the morphologic findings with the clinical history and laboratory data, ultimately arriving at a pathological diagnosis. A renal pathologist is a physician who has undergone general training in anatomic pathology and additional specially training in the interpretation of renal biopsy specimens. Ideally, multiple core sections are obtained and evaluated for adequacy (presence of glomeruli) intraoperatively. A pathologist/pathology assistant divides the specimen(s) for submission for light microscopy, immunofluorescence microscopy and electron microscopy. The pathologist will examine the specimen using light microscopy with multiple staining techniques (hematoxylin and eosin/H&E, PAS, trichrome, silver stain) on multiple level sections. Multiple immunofluorescence stains are performed to evaluate for antibody, protein and complement deposition. Finally, ultra-structural examination is performed with electron microscopy and may reveal the presence of electron-dense deposits or other characteristic abnormalities that may suggest an etiology for the patient's renal disease.

Other animals

In the majority of vertebrates, the mesonephros persists into the adult, albeit usually fused with the more advanced metanephros; only in amniotes is the mesonephros restricted to the embryo. The kidneys of fish and amphibians are typically narrow, elongated organs, occupying a significant portion of the trunk. The collecting ducts from each cluster of nephrons usually drain into an archinephric duct, which is homologous with the vas deferens of amniotes. However, the situation is not always so simple; in cartilaginous fish and some amphibians, there is also a shorter duct, similar to the amniote ureter, which drains the posterior (metanephric) parts of the kidney, and joins with the archinephric duct at the bladder or cloaca. Indeed, in many cartilaginous fish, the anterior portion of the kidney may degenerate or cease to function altogether in the adult. In the most primitive vertebrates, the hagfish and lampreys, the kidney is unusually simple: it consists of a row of nephrons, each emptying directly into the archinephric duct. Invertebrates may possess excretory organs that are sometimes referred to as "kidneys", but, even in Amphioxus, these are never homologous with the kidneys of vertebrates, and are more accurately referred to by other names, such as nephridia. n parasite in the kidney of the African clawed frog Xenopus laevis]] In amphibians, kidneys and the urinary bladder harbour specialized parasites, monogeneans of the family Polystomatidae. The kidneys of reptiles consist of a number of lobules arranged in a broadly linear pattern. Each lobule contains a single branch of the ureter in its centre, into which the collecting ducts empty. Reptiles have relatively few nephrons compared with other amniotes of a similar size, possibly because of their lower metabolic rate. Birds have relatively large, elongated kidneys, each of which is divided into three or more distinct lobes. The lobes consists of several small, irregularly arranged, lobules, each centred on a branch of the ureter. Birds have small glomeruli, but about twice as many nephrons as similarly sized mammals. The human kidney is fairly typical of that of mammals. Distinctive features of the mammalian kidney, in comparison with that of other vertebrates, include the presence of the renal pelvis and renal pyramids, and of a clearly distinguishable cortex and medulla. The latter feature is due to the presence of elongated loops of Henle; these are much shorter in birds, and not truly present in other vertebrates (although the nephron often has a short intermediate segment between the convoluted tubules). It is only in mammals that the kidney takes on its classical "kidney" shape, although there are some exceptions, such as the multilobed reniculate kidneys of pinnipeds and cetaceans.

Evolutionary adaptation

Kidneys of various animals show evidence of evolutionary adaptation and have long been studied in ecophysiology and comparative physiology. Kidney morphology, often indexed as the relative medullary thickness, is associated with habitat aridity among species of mammals, and diet (e.g., carnivores have only long loops of Henle).

Society and culture

Kidneys as food

The kidneys, like other offal, can be cooked and eaten. Kidneys are usually grilled or sautéed, but in more complex dishes they are stewed with a sauce that will improve their flavor. In many preparations, kidneys are combined with pieces of meat or liver, as in mixed grill. Dishes include the British steak and kidney pie, the Swedish hökarpanna (pork and kidney stew), the French rognons de veau sauce moutarde (veal kidneys in mustard sauce) and the Spanish riñones al Jerez (kidneys stewed in sherry sauce) . Rognons dans les recettes

History

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,The Patient as Person: Explorations in Medical Ethics p. 60 by Paul Ramsey, Margaret Farley, Albert Jonsen, William F. May (2002)History of Nephrology 2 p. 235 by International Association for the History of Nephrology Congress, Garabed Eknoyan, Spyros G. Marketos, Natale G. De Santo, 1997; Reprint of American Journal of Nephrology; v. 14, no. 4–6, 1994. 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. Similarly, the Talmud (Berakhoth 61.a) states that one of the two kidneys counsels what is good, and the other evil. According to studies in modern and ancient Hebrew, various body organs in humans and animals served also an emotional or logical role, today mostly attributed to the brain and the endocrine system. The kidney is mentioned in several biblical verses in conjunction with the heart, much as the bowels were understood to be the "seat" of emotion - grief, joy and pain. Body Metaphors in Biblical Hebrew In the sacrifices offered at the biblical Tabernacle and later on at the temple in Jerusalem, the priests were instructed Leviticus 3: 4, 10 and 15 to remove the kidneys and the adrenal gland covering the kidneys of the sheep, goat and cattle offerings, and to burn them on the altar, as the holy part of the "offering for God" never to be eaten.ie Deut 3:4,9,10,15... or the Babylonian Talmud, Bechorot (39a) Ch6:Tr2... In ancient India, according to the Ayurvedic medical systems, the kidneys were considered the beginning of the excursion channels system, the 'head' of the Mutra Srotas, 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.http://www.ayurvedacollege.com/articles/drhalpern/Vata_Doshas Vata Dosha Modern Ayurveda practitioners, a practice which is characterized as pseudoscience, List of topics characterized as pseudoscience, according to the American Medical Association's Report 12 of the Council of Scientific Afairs (A-97) and claims by skeptics ('The Skeptics Dictionary' website) have attempted to revive these methods in medical procedures as part of Ayurveda Urine therapy. These procedures have been called "nonsensical" by skeptics.A Few Thoughts on Ayurvedic Mumbo-Jumbo, Stephen Barrett, M.D, head of the National Council Against Health Fraud NGO and owner of the QuackWatch website. In ancient Egypt, the kidneys, like the heart, were left inside the mummified bodies, unlike other organs which were removed. Comparing this to the biblical statements, and to drawings of human body with the heart and two kidneys portraying a set of scales for weighing justice, it seems that the Egyptian beliefs had also connected the kidneys with judgement and perhaps with moral decisions.

Additional images

File:Slide22222.JPG| Kidney Posterior View File:Slide42222.JPG|Anterior relation of Left Kidney File:Blausen 0593 KidneyAnatomy 02.png|Structure of a Kidney File:Blausen 0592 KidneyAnatomy 01.png|Kidney Anatomy File:Mammal kidneys- FMVZ USP-21.jpg|Kidneys of a mammal after the technique of vinylite and corrosion. File:Kidney Cross Section.png|Kidney Cross Section

See also

References

External links

"green air" © 2007 - Ingo Malchow, Webdesign Neustrelitz
This article based upon the http://en.wikipedia.org/wiki/Kidney, the free encyclopaedia Wikipedia and is licensed under the GNU Free Documentation License.
Further informations available on the list of authors and history: http://en.wikipedia.org/w/index.php?title=Kidney&action=history
presented by: Ingo Malchow, Mirower Bogen 22, 17235 Neustrelitz, Germany