**Core Concept**
Intrinsic renal failure due to ischemic acute tubular necrosis (ATN) involves the disruption of normal renal function resulting from acute ischemia to the renal parenchyma. This condition is characterized by the damage to the renal tubular cells, leading to a decrease in glomerular filtration rate (GFR) and subsequent accumulation of waste products in the body.

**Why the Correct Answer is Right**
Ischemic ATN occurs due to a sudden reduction in renal blood flow, leading to a decrease in oxygen delivery to the renal tubular cells. This results in cellular injury and eventually necrosis. The renal tubular cells are particularly susceptible to ischemic injury due to their high metabolic rate and reliance on aerobic metabolism. The disruption of normal renal function in ischemic ATN is associated with the activation of various inflammatory pathways and the release of pro-inflammatory cytokines.

**Why Each Wrong Option is Incorrect**
**Option A:** This statement is actually true about intrinsic renal failure in case of ischemic ATN. The condition is characterized by the presence of cellular casts in the urine, which are composed of desquamated renal tubular cells.
**Option B:** This statement is also true about intrinsic renal failure in case of ischemic ATN. The condition is associated with an increase in serum creatinine levels, indicating a decrease in GFR.
**Option C:** This statement is not true about intrinsic renal failure in case of ischemic ATN. Ischemic ATN is characterized by the disruption of normal renal function, leading to a decrease in GFR and the accumulation of waste products in the body.

**Clinical Pearl / High-Yield Fact**
One important clinical correlation to remember is that the severity of ischemic ATN can be influenced by the duration and extent of renal ischemia. Prompt recognition and treatment of the underlying cause of renal ischemia are critical in preventing or minimizing renal damage.

**Correct Answer: C. Ischemic ATN is characterized by the disruption of normal renal function, leading to a decrease in GFR and the accumulation of waste products in the body.**