Kidney and renal tract disorders are conditions affecting the function of the body's urinary system, which involves the kidneys, ureters, bladder and urethra . These organs play a primary role in the regulation of chemical balance within the body by filtering and excreting blood-borne wastes and excess fluid.
Most people have two kidneys, which are located just below the rib cage on either side of the spine. Each kidney is about 11.5 centimetres long, 5-7.5 centimetres broad and 2.5 centimetres thick, and weighs about 150 grams  .
The kidneys have several functions that are necessary for maintaining life . The major job of the kidneys is to remove waste from the blood and eliminate it in the urine. In order to do this, the kidneys filter the entire blood supply every two minutes. The filtering is done by tiny clusters of looping blood vessels, each of which is known as a glomerulus (derived from the Greek word for filter; the plural word is glomeruli). There are approximately 1 million glomeruli in each kidney. Blood is filtered in the glomeruli, and water and wastes pass into the tubules and become urine.
The kidneys also keep the right amount of fluid in the body by making more urine when there is too much fluid, and by reducing urinary output when the body has less fluid than required (such as when a person is dehydrated) . The water to be eliminated from the body as urine passes from the kidneys to the bladder via the ureters - two thin-walled tubes of around 30 centimetres in length (the left ureter is slightly longer than the right) . This urine is stored in the bladder - a muscular, distensible reservoir with a capacity of around 500 millilitres - and is then discharged from the body via the urethra.
The kidneys also help control blood pressure by producing a chemical called renin . Several other chemicals are produced and released by the kidneys as a part of maintaining body balances.
The kidneys and each of the components of the urinary tract is subject to a variety of adverse conditions that may affect the filtration and excretion process and alter the body's chemical balance  . Disorders of the kidneys and urinary tract range in severity. End-stage renal disease (ESRD) is the most severe disorder, but other less serious conditions may facilitate progression to this stage of kidney disease which, if left untreated, results in death.
The pathological conditions of the kidney and urinary tract can be divided generally into two groups , . The first encompasses conditions that result in damage to the kidneys (broadly referred to as renal disorders) such as glomerulonephritis and renal failure. The second includes disorders of the urinary tract, such as urinary tract infections. However, a few conditions (for example, urolithiasis) are more difficult to categorise as they may affect the components of either sub-system.
Kidney and urinary tract disorders are generally attributed to various combinations of multiple risk factors including: infections, heavy drinking, smoking, dietary factors, low birthweight and infant malnutrition, increasing adult weight, genetic susceptibility, and the signs of syndrome X (increasing blood pressure, insulin, blood glucose and lipid levels)  . The contributory role of syndrome X in the development of kidney dysfunction is of particular note as it links renal disease with a range of other chronic conditions, specifically type 2 diabetes, hypertension and cardiovascular disease.
Renal failure occurs when the kidneys allow harmful waste products to build up in the body . The failure can be acute - having a rapid onset and generally a relatively short course - or chronic - of long duration.
Acute renal failure may be due to trauma, conditions that impair the blood flow to the kidneys, some toxic substances (such as mercury compounds, carbon tetrachloride, or ethylene glycol), bacterial toxins, glomerulonephritis, or acute obstruction of the urinary tract . Treatment consists of specific therapy for the primary condition and either peritoneal dialysis or haemodialysis.
Chronic renal failure is a slow and progressive loss of kidney function over several years, often resulting in permanent kidney failure, known as end-stage renal disease (ESRD) . People with ESRD need dialysis or transplantation to replace the work of the kidneys.
Glomerulonephritis refers to a number of conditions that result in inflammation of the glomeruli and subsequent damage to the filtration process of the kidney  . This condition may be acute, subacute or chronic . Acute glomerulonephritis, also known as acute nephritic syndrome, frequently follows infections, especially those of the upper respiratory tract caused by particular strains of streptococcal bacteria.
Of the various conditions that are encompassed by the term glomerulonephritis, acute post-streptococcal glomerulonephritis (APSGN) continues to pose a significant public health problem in developing countries and among Indigenous populations of the developed world. APSGN is a potentially serious, non-suppurative condition that occurs two to three weeks after skin or throat infection with nephritogenic strains of group A streptococcal streptococci (GAS) .
Glomerular diseases damage the glomeruli, initially letting protein and sometimes red blood cells leak into the urine . Glomerular disease can also interfere with clearance of waste products by the kidney, allowing them to build up in the blood. Loss of blood proteins like albumin in the urine can result in a fall in their level in the bloodstream, resulting in a reduced capacity of blood to absorb extra fluid from the body. Fluid can then accumulate outside the circulatory system in the face, hands, feet, or ankles and cause swelling.
A urinary tract infection (UTI) is an infection anywhere in the urinary tract . UTIs are usually caused by bacteria that can also live in the digestive tract, in the vagina, or around the urethra. These bacteria can enter the urethra and travel to the bladder, where they are usually flushed out with urine and do not cause an infection. On occasions and among some people (women are more prone to UTI than men, and older people are more prone that younger people) the bacteria multiply sufficiently to cause an infection.
A UTI may be present despite few physical symptoms, but lower urinary tract infection is typically associated with frequent, painful urination, and tenderness in the lower pelvic area . Upper urinary tract infection is associated with a range of clinical features, most commonly: fever, back or loin pain; and chills and rigors  . Single episodes of UTI rarely have serious consequences, but recurrent or persistent infections may promote kidney damage when coupled with conditions such as diabetes.
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