Watershed areas are found in the brain, where areas are perfused by both the anterior and middle cerebral arteries, and in the intestines, where areas are perfused by both the superior and inferior mesenteric arteries (i.e., splenic flexure).
Critical areas are situated in the brain, where regions are supplied by both the anterior and middle cerebral arteries, and in the intestines, where regions are nourished by both the superior and inferior mesenteric arteries, particularly at the splenic flexure.