The median distance between the dentate line and the anal verge was 2.0 cm. The distances of each rectal valve (proximal to distal) to the anal verge and dentate line were 11.4 ± 2.0 cm, 8.6 ± 2.0 cm, 6.0 ± 1.7 cm and 9.1 ± 1.6 cm, 6.3 ± 1.6 cm, 3.7 ± 1.5 cm, respectively.

The average length of the anatomic anal canal (dentate line to anal verge) was 2.1 cm (range 1.0-3.8 cm). In men, the average length was 2.2 cm (range 1.4-3.8 cm), whereas in women the average length was 2.0 cm (range 1.0-3.2 cm) (P less than . 01).

The dentate line is located one third below the entire surgical anal canal. The area between the dentate line and the anal verge is called the “anoderm,” which is a nonkeratinized squamous epithelium and has no structures such as hair follicles or glands. It is also soft when palpated and sensitive to pain.

The anorectal line is localized at the highest aspect of these ridges. Multiple anal glands are present along the caudal aspect of the anal columns. They are responsible for secreting lubricating mucus during defecation. The dentate or pectinate line demarcates the junction of the cranial and caudal anal canal.

The external anal sphincter is composed of skeletal muscle that functions like other postural muscles in the body. It is a voluntary muscle that responds to volitional commands to contract and maintain continence when feces are propelled through a relaxed internal anal sphincter into the rectum.

Proctitis can cause rectal pain, diarrhea, bleeding and discharge, as well as the continuous feeling that you need to have a bowel movement. Proctitis symptoms can be short-lived, or they can become chronic.

Hemorrhoids happen when anal blood vessels are swollen. Straining to pass stool or being constipated are often the causes of hemorrhoids. When you have a hemorrhoid, you may feel a lump near your anus. The pain may be generally dull but sharp when you sit down.