Definition of hemorrhoid
Hemorrhoids (Piles) are blood vessels located in the smooth muscles of the walls of the rectum and anus. They are a normal part of the anatomy and are located at the junction where small arteries merge into veins. They are cushioned by smooth muscles and connective tissue and are classified by where they are located in relationship to the pectinate line, the dividing point between the upper 2/3 and lower 1/3 of the anus. This is an important anatomic distinction because of the type of cells that line the hemorrhoid, and the nerves that provide sensation.
Internal hemorrhoids are located above the pectinate line and are covered with cells that are the same as those that line the rest of the intestines. External hemorrhoids arise below the line and are covered with cells that resemble skin.