In postrenal AKI, what happens when the blockage occurs?

In postrenal AKI, what happens when the blockage occurs?

• A. Urine backs up into the kidney
• B. Urine flows freely to bladder
• C. Kidney stones dissolve spontaneously
• D. GFR increases

Answer: (A)

When urine flow is blocked downstream of the kidneys, urine backs up into the renal collecting system. That backpressure raises pressure inside the kidney, especially in the tubules, which lowers the net filtration pressure across the glomerulus and reduces the glomerular filtration rate. If the obstruction isn’t relieved, this backpressure can cause hydronephrosis and progressive kidney injury. So the hallmark of postrenal AKI is urine backing up into the kidney. The other ideas don’t fit: urine would continue to flow to the bladder only if there were no blockage; kidney stones don’t spontaneously dissolve because of obstruction, and GFR would not increase—in fact it decreases with blocked outflow.

When urine flow is blocked downstream of the kidneys, urine backs up into the renal collecting system. That backpressure raises pressure inside the kidney, especially in the tubules, which lowers the net filtration pressure across the glomerulus and reduces the glomerular filtration rate. If the obstruction isn’t relieved, this backpressure can cause hydronephrosis and progressive kidney injury. So the hallmark of postrenal AKI is urine backing up into the kidney. The other ideas don’t fit: urine would continue to flow to the bladder only if there were no blockage; kidney stones don’t spontaneously dissolve because of obstruction, and GFR would not increase—in fact it decreases with blocked outflow.