Acid excretion and nitrogenous metabolite excretion are impaired with the loss of kidney function. History
Urea was crystallized and identified between 1797 and 1808. Urea was hypothesized to be the source of urinary ammonia during this time and was confirmed in 1817. It was hypothesized that excess urea may lead to specific disorders. Later in 1821, it was confirmed that the body did produce urea and that it was excreted by the kidneys. In 1827, urea was first synthesized in the lab, confirming the composition of urea and making it the first biological substance synthesized. In 1856, urea was produced in vitro via oxidation of proteins. It was in 1827 that Henri Dutrochet seeded the idea of dialysis with the discovery of separating smaller molecules from larger molecules through a semipermeable membrane. It was in 1829 and 1831 when convincing proof was obtained that in certain patients, blood urea was elevated. They also suggested that harm may be caused by this. Later research suggested that major neurological disorders like coma and convulsions did not correlate with physical findings which included generalized edema of the brain. This suggested that uremia was a form of blood poisoning. In 1851, E.T. Frerich described clinical uremic syndrome and suggested that a toxicity was the mechanism of its cause. It was in 1856 that J. Picard developed a sensitive method to reproducibly measure blood urea. He was able to detect a 40% decrease of urea concentration between the renal artery and the renal vein.
There are more than 90 different compounds that have been identified. Some of these compounds can be toxic to the body. Uremic toxins
Uremic toxins are any biologically active compounds that are retained due to kidney impairment. Many uremic salts can also be uremic toxins.Urea was one of the first metabolites identified. Its removal is directly related to patient survival but its effect on the body is not yet clear. Still, it is not certain that the symptoms currently associated with uremia are actually caused by excess urea, as one study showed that uremic symptoms were relieved by initiation of dialysis, even when urea was added to the dialysate to maintain the blood urea nitrogen level at approximately 90 mg per deciliter (that is, approximately 32 mmol per liter). Urea could be the precursor of more toxic molecules but it is more likely that damage done to the body is from a combination of different compounds which may act as enzyme inhibitors or derange membrane transport. Indoxyl sulfate is one of the better characterized uremic toxins. Indoxyl sulfate has been shown to aggravate vascular inflammation in atherosclerosis by modulating macrophage behavior. Biochemical characteristics
Many regulatory functions of the body are affected. Regulation of body fluids, salt retention, acid and nitrogenous metabolite excretion are all impaired and can fluctuate widely. Body fluid regulation is impaired due to a failure to excrete fluids, or due to fluid loss from vomiting or diarrhea. Regulation of salt is impaired when salt intake is low or the vascular volume is inadequate.