Acute tubular necrosis, regenerative (polyuric) phase
Click picture to enlarge. Close window to return

As the renal tubular epithelium regenerates, as the double nucleus (arrow) in this photomicrograph testifies to, the kidney begins to produce large amounts of very dilute urine. The reason for this is that the complicated brush border cells do not come back immediately, they are first replaced by low cuboidal epithelium, which does little in the way of resorption of water. Thus large quantities of dilute urine (polyuria) are produced by the patient. Eventually, the epithelium differentiates into the more complex brush border type, and normal urinary production is restored.