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

The area affected in the ischemic region of the liver is specifically the zone III area, also known as the perivenous region. This zone is located around the central vein of the liver lobule and is particularly susceptible to ischemic damage due to its position and the characteristics of blood flow in the liver.

Zone III is the last area to receive oxygenated blood after it has perfused through the earlier zones (zone I and zone II), making it the most vulnerable to conditions such as hypoxia, reduced blood flow, or toxic injury. In situations of liver ischemia, such as in cases of shock, heart failure, or cirrhosis, zone III hepatocytes are the first to suffer damage due to their relative lack of oxygen and nutrients compared to the other zones.

The other options do not relate to hepatic ischemia directly. The rectum, renal cysts, and cutaneous angiofibromas involve systems or conditions that do not characterize the liver's limited blood supply or ischemic responses. Understanding the vulnerability of zone III is crucial in assessing liver injury and understanding related pathophysiological concepts.