Pectinate line
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The pectinate line (dentate line) is a line which divides the upper two-thirds and lower third of the anal canal. Developmentally, this line represents the hindgut-proctodeum junction.
It is an important anatomical landmark in humans, and forms the boundary between the anal canal and the rectum according to the anatomic definition.[1] Colorectal surgeons instead define the anal canal as the zone from the anal verge to the anorectal ring (palpable structure formed by the external anal sphincter and the puborectalis muscle).[1] Several distinctions can be made based upon the location of a structure relative to the pectinate line:
| Distinction | Above pectinate line | Below pectinate line |
|---|---|---|
| Lymph drainage | internal iliac[2] | superficial inguinal lymph nodes (below Hilton's white line) |
| Epithelium | columnar epithelium (as is most of the digestive tract - the line represents the end of the part of the body derived from the hindgut) | stratified squamous epithelium, non-keratinized (until Hilton's white line, where the anal verge becomes continuous with the perianal skin containing keratinized epithelium.) |
| Embryological origin[3] | endoderm | ectoderm |
| Artery | superior rectal artery | middle and inferior rectal arteries |
| Vein | superior rectal vein draining into the inferior mesenteric vein and subsequently the hepatic portal system | middle and inferior rectal veins |
| Hemorrhoids classification | internal hemorrhoids (not painful) | external hemorrhoids (painful) |
| Nerves | inferior hypogastric plexus | pudendal nerves |
Additional images
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Microscopic cross section of the anorectal junction
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Anatomy of the anus and rectum
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Coronal section of rectum and anal canal
References
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