USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

What characterizes the ischemic area of the kidney?

1. Splenic flexure

2. Straight segment of proximal tubule (medulla)

3. Thick ascending limb (medulla)

4. Cardiac rhabdoyomas in ventricular walls and AV valves

The correct answer is: Straight segment of proximal tubule (medulla)

The correct answer focuses on the characteristics of the ischemic area of the kidney, specifically the straight segment of the proximal tubule located in the medulla. This area is particularly vulnerable to ischemia for several reasons: it relies heavily on a stable blood supply and has a high oxygen demand due to the active reabsorption processes that occur there. In situations of reduced blood flow or renal artery occlusion, this region can suffer from cellular necrosis and dysfunction as it is located farthest from the renal artery branches, making it more prone to ischemic injury. While the thick ascending limb also plays a role in kidney function and can be affected by ischemia, it is less commonly acknowledged as the primary area impacted in acute ischemic events compared to the straight segment of the proximal tubule. Other options, such as the splenic flexure and cardiac rhabdomyomas, do not relate to renal ischemia. The splenic flexure pertains to gastrointestinal blood supply and is linked implicitly with watershed areas; rhabdomyomas are tumors primarily associated with cardiac tissue, rather than renal pathology. Thus, understanding the specific vulnerabilities of different kidney segments is crucial in identifying the correct characterization of the ischemic area.