| Name | Kidney |
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| Latin | ren |
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| Graysubject | 253 |
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| Graypage | 1215 |
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| Caption | Human kidneys viewed from behind with spine removed |
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| Image2 | Lammnieren.jpg |
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| Caption2 | Lamb kidneys |
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| Artery | renal artery |
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| Vein | renal vein |
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| Nerve | renal plexus |
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| Meshname | Kidney |
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| Meshnumber | A05.810.453 |
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| Dorlands | five/000056330 |
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| Dorlandsid | Kidney |
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The kidney are organs with several functions. They are seen in many types of animals, including vertebrates and some invertebrates. They are an essential part of the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid-base balance, and regulation of blood pressure. They serve the body as a natural filter of the blood, and remove wastes which are diverted to the urinary bladder. In producing urine, the kidneys excrete wastes such as urea and ammonium; the kidneys also are responsible for the reabsorption of water, glucose, and amino acids. The kidneys also produce hormones including calcitriol, renin, and erythropoietin.
Located at the rear of the abdominal cavity in the retroperitoneum, the kidneys receive blood from the paired renal arteries, and drain into the paired renal veins. Each kidney excretes urine into a ureter, itself a paired structure that empties into the urinary bladder.
Renal physiology is the study of kidney function, while nephrology is the medical specialty concerned with kidney diseases. Diseases of the kidney are diverse, but individuals with kidney disease frequently display characteristic clinical features. Common clinical conditions involving the kidney include the nephritic and nephrotic syndromes, renal cysts, acute kidney injury, chronic kidney disease, urinary tract infection, nephrolithiasis, and urinary tract obstruction. Various cancers of the kidney exist; the most common adult renal cancer is renal cell carcinoma. Cancers, cysts, and some other renal conditions can be managed with removal of the kidney, or nephrectomy. When renal function, measured by glomerular filtration rate, is persistently poor, dialysis and kidney transplantation may be treatment options. Although they are not severely harmful, kidney stones can be a pain and a nuisance. The removal of kidney stones includes sound wave treatment, which breaks up the stones into smaller pieces which are then passed through the urinary tract. One common symptom of kidney stones is a sharp pain in the medial/lateral segments of the lower back.
Anatomy
Location
, showing kidneys at the level of T12 to L3. ]]
In humans, the kidneys are located in the
abdominal cavity, and lie in a
retroperitoneal position. There are two, one on each side of the spine. The asymmetry within the abdominal cavity caused by the liver typically results in the right kidney being slightly lower than the left, and left kidney being located slightly more medial than the right. The left kidney is approximately at the vertebral level T12 to L3, and the right slightly lower. The right kidney sits just below the
diaphragm and posterior to the
liver, the left below the diaphragm and posterior to the
spleen. Resting on top of each kidney is an
adrenal gland. The upper (cranial) parts of the kidneys are partially protected by the eleventh and twelfth
ribs, and each whole kidney and adrenal gland are surrounded by two layers of fat (the perirenal and pararenal fat) and the
renal fascia. Each adult kidney weighs between 125 and 170 grams in males and between 115 and 155 grams in females. The left kidney is typically slightly larger than the right.
Structure
[[File:KidneyStructures PioM.svg|thumb|250px|left|
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. Minor calyx •
15. Major calyx •
16. Renal papilla •
17. Renal column
]]
The kidney has a bean-shaped structure, each kidney has concave and convex surfaces. The concave surface, the renal hilum, is the point at which the renal artery enters the organ, and the renal vein and ureter leave. The kidney is surrounded by tough fibrous tissue, the renal capsule, which is itself surrounded by perinephric fat, renal fascia (of Gerota) and paranephric fat. The anterior (front) border of these tissues is the peritoneum, while the posterior (rear) border is the transversalis fascia.
The superior border of the right kidney is adjacent to the liver; and the spleen, for the left border. Therefore, both move down on inhalation.
The kidney is approximately 11–14 cm in length, 6 cm wide and 4 cm thick.
The substance, or parenchyma, of the kidney is divided into two major structures: superficial is the renal cortex and deep is the renal medulla. Grossly, these structures take the shape of 8 to 18 cone-shaped renal lobes, each containing renal cortex surrounding a portion of medulla called a renal pyramid (of Malpighi). Input from the sympathetic nervous system triggers vasoconstriction in the kidney, thereby reducing renal blood flow.
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.
Etymology
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.
Diseases and disorders
Congenital
Congenital hydronephrosis
Congenital obstruction of urinary tract
Duplex kidneys, or double kidneys, occur in approximately 1% of the population. The normally cause no complications, but, occasionally, can cause urine infections.
Duplicated ureter occurs in approximately one in 100 live births
Horseshoe kidney occurs in approximately one in 400 live births
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 is invariably fatal.
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
Acquired
.]]
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 stones (nephrolithiasis) 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 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
* Stage 5 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 will chronic kidney disease develop. 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.
In 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.
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. 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. Similarly, the Talmud (Berakhoth 61.a) states that one of the two kidneys counsels what is good, and the other evil.
Animal kidneys as food
The kidneys of animals can be
cooked and eaten by humans (along with other
offal).
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 or meurav Yerushalmi. Among the most reputed kidney dishes, 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), deserve special mention.
See also
Artificial kidney
Organ donation
Organ harvesting
Pelvic kidney
World Kidney Day
References
External links
The Kidney Foundation of Canada
electron microscopic images of the kidney (Dr. Jastrow's EM-Atlas)
European Renal Genome project kidney function tutorial
Kidney Foundation of Canada kidney disease information
Renal Fellow Network: Structure & Function of Other Animals' Kidneys
Kidney Diseases
Kidney Information
Animated Presentatin on Kidney Function
