Which condition could lead to postrenal failure as a result of urinary obstruction?

Postrenal failure occurs when there is an obstruction in the urinary tract that prevents urine from being expelled from the kidneys. This obstruction can arise from various causes, including structural blockage. A kinked ureter is a perfect example of such a condition, as it directly interferes with the normal flow of urine from the kidney to the bladder. When the ureter is kinked, urine can accumulate in the kidney, leading to increased pressure and ultimately kidney dysfunction.

In contrast, severe dehydration can lead to prerenal failure due to decreased blood volume and flow to the kidneys, rather than an obstruction. Heart disease can affect renal perfusion but does not directly cause urinary obstruction. Kidney disease itself often involves intrinsic issues within the kidney, impacting its function but not causing obstruction in the urinary tract.

Thus, a kinked ureter exemplifies a clear mechanical obstruction leading to postrenal failure, making it the correct choice.