Disorders of the Excretory System, Dialysis and Kidney Transplant

When the kidneys are damaged by disease, injury or long-term strain, or when the passages that carry urine out of the body become obstructed or inflamed, a range of disorders can result, several of which are serious enough to be life-threatening if left untreated, and modern medicine has developed effective ways of managing even complete kidney failure.

Uremia is the general term for the toxic condition that arises when the kidneys fail to filter and excrete nitrogenous wastes — chiefly urea, but also creatinine and other by-products — adequately, so that these substances accumulate to abnormally high levels in the blood. Because these wastes are toxic to many tissues at high concentration, uremia produces a wide range of symptoms, including nausea, loss of appetite, fatigue, confusion and, if the underlying kidney failure is not corrected or treated, progression to coma and death; uremia is best understood as a consequence of underlying renal failure rather than a separate disease in its own right.

Renal failure is the broader condition of the kidney losing its ability to filter blood and produce urine adequately, and it is usually classified into two forms. Acute renal failure develops suddenly, over hours to days, and can follow severe shock, poisoning by certain drugs or toxins, a sudden and severe drop in blood pressure, or obstruction of the urinary tract; if the underlying cause is identified and treated promptly, acute renal failure is often at least partly reversible. Chronic renal failure, by contrast, develops slowly over months or years, most often as a consequence of long-standing conditions such as hypertension, diabetes mellitus, or repeated/persistent glomerulonephritis, and involves the gradual, usually irreversible, loss of functioning nephrons; if it progresses far enough, chronic renal failure leads to end-stage renal disease, in which the kidneys can no longer sustain life without medical intervention.

Renal calculi, commonly called kidney stones, are hard, crystalline deposits — most often made of calcium oxalate or calcium phosphate, though other compositions occur — that form when certain salts present in the urine at unusually high concentration crystallise out and clump together within the kidney or ureter, often encouraged by chronically low fluid intake (which keeps the urine more concentrated than usual) or a diet particularly rich in oxalate- or calcium-containing foods. A stone lodged in the ureter can cause severe, cramping pain known as renal colic as the ureter's smooth muscle contracts around it, and if the stone is large enough it may obstruct the flow of urine, with the risk of back-pressure damage to the kidney if not relieved.

Nephritis is the general term for inflammation of the nephrons, and the most clinically important form is glomerulonephritis, inflammation specifically affecting the glomerulus and its filtration membrane. It is most often triggered by an immune or allergic reaction — classically following a streptococcal throat infection, where antibodies formed against the bacteria go on to damage the glomerular filtration membrane as an unintended side effect — and it results in blood and/or protein leaking abnormally into the urine, reduced glomerular filtration, and fluid retention that can cause visible swelling. …