The pectinate (dentate) line is a wavy line around the anal canal formed by the anal valves at the bases of the anal columns, about 2 cm above the anal opening. It marks the approximate junction between the embryonic hindgut above and the ectodermal anal pit below. Almost everything about the canal, including lining, nerves, blood vessels and lymphatics, changes at this line.
| Location | Anal canal, about 2 cm above the anal verge, at the level of the anal valves |
|---|---|
| Parts |
|
| Nerve Supply | Autonomic fibres from the inferior hypogastric plexus (above); Inferior rectal nerves from the pudendal nerve (below) |
| Blood Supply | Superior rectal artery (above); Inferior rectal arteries (below) |
| Venous drainage |
|
| Lymphatic drainage |
|
Marks the boundary between the visceral and somatic territories of the anal canal and the openings of the anal glands.
Above the line, the lining is columnar and largely insensitive, so internal haemorrhoids and injections or banding cause little pain; below it, the lining is squamous and supplied by somatic nerves, so external haemorrhoids and fissures are very painful. Tumours above tend to be adenocarcinomas draining to internal iliac nodes, while those below are usually squamous cell carcinomas draining to superficial inguinal nodes.
Enlarged vascular cushions above the pectinate line that bleed painlessly and are treated with banding or injection.
Swollen veins below the pectinate line that can thrombose and cause acute severe pain.
Cancer of the anal lining around and below the pectinate line, strongly associated with human papillomavirus.
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