What occurs when there is significant obstruction in the urinary tract?

When there is significant obstruction in the urinary tract, urinary stasis occurs due to the inability of urine to flow freely from the kidneys through the ureters to the bladder. This stasis can lead to several complications, including the risk of infection, bladder distension, and further kidney damage.

It's important to recognize that while urinary stasis is a direct consequence of obstruction, conditions like renal failure, high blood pressure, and urethritis can also be related to urinary tract issues but are not the immediate result of obstruction alone. Renal failure may occur if the obstruction is severe and prolonged, but it is not the direct or initial outcome of the obstruction itself. High blood pressure can be affected by renal function over time, but it is not a direct consequence of urinary tract obstruction. Urethritis, which is inflammation of the urethra, can arise from infection as a complication of urinary stasis, but again, it is not the primary or immediate effect of obstruction.

Thus, urinary stasis is the most accurate answer, as it directly outlines the condition that arises due to significant obstruction in the urinary tract.