Renal Tubular Acidosis

Posted by e-Medical PPT Sunday, September 19, 2010
Renal tubular acidosis is a medical disorder that involves an accumulation of acid in the body due to a malfunction of the kidneys to appropriately acidify the urine.When blood is filtered by the kidney, the filtrate passes through the tubules of the nephron, allowing for exchange of salts, acid equivalents, and other solutes before it drains into the bladder as urine. The metabolic acidosis that results from RTA may be caused either by failure to recover sufficient bicarbonate ions from the filtrate in the proximal tubule or by insufficient secretion of hydrogen ions into the latter portions of the nephron (distal tubule). Although a metabolic acidosis also occurs in those with renal insufficiency, the term renal tubular acidosis is reserved for individuals with poor urinary acidification in otherwise well-functioning kidneys.The metabolic acidosis caused by RTA is a normal anion gap acidosis. Several different types of RTA exist, which all have different syndromes and different causes.
Distal or type 1 RTA is the classical form of RTA, being the first described. Distal RTA is characterized by a failure of acid secretion by the alpha intercalated cells of the cortical collecting duct of the distal nephron.
This leads to these clinical features
* Normal anion gap metabolic acidosis/acidemia
* Hypokalemia
* Urinary stone formation (related to alkaline urine, hypercalciuria, and low urinary citrate).
* Nephrocalcinosis
* Bone demineralisation (causing rickets in children and osteomalacia in adults)
Proximal or type 2RTA is caused by a failure of the proximal tubular cells to reabsorb filtered bicarbonate from the urine, leading to urinary bicarbonate wasting and subsequent acidemia.
In some patients, their RTA shares features of both Distal and Proximal types.
Type 4 RTA is not actually a tubular disorder at all and nor does it have a clinical syndrome similar to the other types of RTA.Its cardinal feature is hyperkalemia, and measured urinary acidification is normal.

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