In which part of the digestive system do internal hemorrhoids occur?

Internal hemorrhoids occur above the pectinate line in the anal canal. The pectinate line serves as an important anatomical landmark in the gastrointestinal tract, distinguishing between different embryological origins of the anal canal. Above this line, the anal canal is lined by rectal mucosa and is supplied by superior rectal artery and venous drainage to the superior mesenteric vein. This region lacks pain fibers from the somatic nervous system, which is why internal hemorrhoids are often not painful unless complications arise.

In contrast, the area below the pectinate line, which is supplied by inferior rectal vessels, is innervated by somatic nerves and is more sensitive to pain, making any issues such as hemorrhoids in that region typically more symptomatic. The ileum and cecum are parts of the small intestine and the beginning of the large intestine, respectively, and are not associated with hemorrhoids at all. Thus, this anatomical knowledge clarifies why choosing the area above the pectinate line is correct regarding the occurrence of internal hemorrhoids.