Hemorrhoids are a problem that affects over 1 million Americans each year. It affects both sexes and is more common in the more prosperous societies, perhaps related to exercise, diet and bowel habits.

Anatomy

• The anal canal is a little over one inch in length (3 cm) and extends from the lowest part of the rectum to the anus (Figure 1)
• The anal canal is surrounded by an internal (inside) and external (outside) venous plexus (interconnection of veins)
• In the anal canal these plexuses form "cushions" of mucosa (inner lining of tissue) filled with veins and muscle fibers. These hemorrhoidal cushions fill up with blood during the act of straining while passing stool, and serve to protect the anus from injury. The muscle fibers help support the cushions
• There are three cushions one each in the left lateral, right posterior and right anterior positions (looking from behind at 9, 2 and 5 o'clock)
• Two muscular sphincters (internal, inside; external, outside) surround the anal canal and control the passage of stool. The sphincters tends to contract to hold in stool when pressure in the abdomen increases and relaxes when a person strains at the stool

Figure 1 - Anatomy of the lower rectum and anus showing the muscle sphincters that control bowel movements and the internal and external plexuses. © C. Scalici