What describes internal hemorrhoids?

Internal hemorrhoids are situated above the pectinate line, which is an important anatomical landmark in the anal canal. This area is innervated by visceral nerves, which do not convey pain sensations like somatic nerves do. As a result, internal hemorrhoids are often painless, even when they bleed. The bleeding associated with internal hemorrhoids commonly occurs during bowel movements and may be noticed as bright red blood on the stool or toilet paper.

The other options describe conditions that are not characteristic of internal hemorrhoids. Painful clots typically refer to external hemorrhoids, which are found below the pectinate line and are innervated by somatic nerves, leading to pain when they become thrombosed. An infection of the rectal wall does not specifically describe hemorrhoids and would indicate a different pathological condition. Swelling of external rectal veins pertains to external hemorrhoids rather than internal ones, which are defined by their location and lack of pain.