or renal transplant

Replacement of a diseased or damaged kidney with one from a living relative or a legally dead donor. The former's tissue type is more likely to match, reducing the chance of rejection; but removal puts the donor at risk, and a kidney from a dead donor is more likely to be available. The new kidney is implanted and its blood vessels and ureter sewn in place. A near-normal life may be resumed within two months, but the drugs that prevent rejection leave the patient vulnerable to infection. Seealso transplant.

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or renal system

System that produces and discharges urine to rid the body of waste products. It consists of the kidneys, which balance electrolytes in blood, retaining and adding needed ones and removing unneeded or dangerous ones for excretion; the ureters, two thin muscular tubes 10–12 in. (25–30 cm) long that move the urine by peristalsis; the hollow, muscular bladder, which receives and stores it; and the urethra, through which it leaves the body. In women the urethra is 1.5 in. (4 cm) long. In men it is longer (since it passes through the penis), about 8 in. (20 cm), and carries semen from the prostate gland as well as urine. Urinary disorders, which can lead to dehydration or edema and to a dangerous buildup of waste and toxic substances, include kidney failure, tumours, and bladder and kidney stones.

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or renal failure

Partial or complete loss of kidney function. Acute failure causes reduced urine output and blood chemical imbalance, including uremia. Most patients recover within six weeks. Damage to various kidney structures can result from chemical exposure, major blood loss, crush injury, hypertension, severe burns, severe kidney infections, diabetes mellitus, renal artery or urinary tract blockage, and liver diseases. Complications include heart failure, pulmonary edema, and high potassium levels. Chronic failure usually results from long-term kidney diseases. The blood becomes too acidic, bones can lose calcium, and nerves can degenerate. The kidneys can sustain life until they lose about 90percnt of their function. If one is removed, the other increases in size and function to compensate. Failure of both usually requires dialysis or kidney transplant.

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or hemodialysis

Process of removing blood from a patient with kidney failure, purifying it with a hemodialyzer (artificial kidney), and returning it to the bloodstream. Many substances (including urea and inorganic salts) in the blood pass through a porous membrane in the machine into a sterile solution; particles such as blood cells and proteins are too large to pass. This process controls the acid-base balance of the blood and its content of water and dissolved materials.

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Any of several types of cysts in the kidneys. Some are present at birth; others are caused by tubular obstruction. Large cysts can cause backaches and a dragging sensation. Multiple cysts occur as a result of various disorders, including kidney vascular diseases, lymphatic vessel blockage, congenital diseases, and tapeworm infestation. The most serious is medullary cystic disease, which has no warning symptoms but causes anemia, low blood sodium levels, and uremia. The kidneys become shrunken, grainy, and scarred. Cysts should usually be checked surgically to rule out cancer. Seealso urogenital malformation.

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or hypernephroma

Malignant tumour of the cells that cover and line the kidney. It usually affects persons over age 50 who have vascular disorders of the kidneys. It seldom causes pain, unless it is advanced. It may metastasize to other organs (e.g., lungs, liver, brain, bone) and go unrecognized until these secondary tumours cause symptoms. Blood can appear in the urine early on but is painless and usually disregarded. Even when the cancer is in the early stages, X-ray films can show deformity in kidney structures.

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or renal calculus

Mass of minerals and organic matter that may form in a kidney. Urine contains many salts in solution, and low fluid volume or high mineral concentration can cause these salts to precipitate and grow, forming stones. Large stones can block urine flow, be a focus for infection, or cause renal colic (painful spasms). They can obstruct the urinary system at various points. Treatment deals with any underlying problem (e.g., infection or obstruction), tries to dissolve stones with drugs or ultrasound (lithotripsy), or removes large ones surgically.

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In biological terms, ultrafiltration occurs at the barrier between the blood and the filtrate in the renal corpuscle or Bowman's capsule in the kidneys. The Bowman's capsule contains a dense capillary network called the glomerulus. Blood flows into these capillaries through a wide afferent arteriole and leaves through a narrower efferent arteriole. The blood pressure inside these capillaries is high because:

1. The renal artery contains blood at very high pressure which enters the glomerulus via the short afferent arteriole.
2. The efferent arteriole has a smaller diameter than the afferent arteriole.

The high pressure forces small molecules such as water, glucose, amino acids, sodium chloride and urea through the filter, from the blood in the glomerular capsule across the basement membrane of the Bowman's capsule and into the nephron. This type of high pressure filtration is ultrafiltration. The fluid formed in this way is called glomerular filtrate.

Glomerular pressure is about 75 millimeters of mercury (10 kPa). It is opposed by osmotic pressure(30 mmHg, 4.0 kPa) and hydrostatic pressure (20 mmHg, 2.7 kPa) of solutes present in capsular space. This difference in pressure is called effective pressure(25 mmHg)(3.3 kPa).

It is also used in hemodialysis to clean whole blood while keeping its composition intact.

Selectivity

The structures of the layers of the glomerulus determine their permeability-selectivity (permselectivity). For instance, small ions such as sodium and potassium pass freely, while larger plasma proteins, such as hemoglobin and albumin have practically no permeability at all.

Slow Continuous Ultrafiltration

Slow Continuous Ultrafiltration (SCUF) is an artificial method which approximately mimics the ultrafiltration function of the kidneys. SCUF is a continuous renal replacement therapy (CRRT) generally used to remove fluid from fluid overloaded patients suffering acute renal failure. During SCUF blood is removed from the body and is passed through an extracorporeal circuit through a hemofilter and a predetermined percentage of plasma water is removed based upon a prescription. Typically, no more than 2 liters an hour of fluid is removed. The remaining blood is returned to the patient. Unlike hemodialysis, hemofiltration and hemodiafiltration, no dialysate or replacement fluids are used in SCUF.

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